Hydroxytyrosol

Hydroxytyrosol at a Glance

Hydroxytyrosol, or 3,4-dihydroxyphenylethanol, is a small catechol phenol (a phenylethanoid) and the principal simple phenol of the olive (Olea europaea). It is the molecule that carries much of the antioxidant reputation of olive leaf, olives and virgin olive oil, and it is one of the most-studied dietary phenols in the literature.

Its defining relationship is to oleuropein: hydroxytyrosol is the active metabolite of that bitter olive glycoside. Oleuropein is poorly absorbed intact and is largely hydrolysed — by plant enzymes, gut microbiota, food processing and simple acid or heat — to hydroxytyrosol, which is the smaller, more absorbable phenol that actually circulates after an olive dose ^{4,6,15Reference 4Rodríguez-Morató J et al. · 2016Metabolic disposition and biological significance of simple phenols of dietary origin: hydroxytyrosol and tyrosolView study →Reference 6de Bock M et al. · 2013Human absorption and metabolism of oleuropein and hydroxytyrosol ingested as olive (Olea europaea L.) leaf extractView study →Reference 15Yuan JJ et al. · 2015Enzymatic hydrolysis of oleuropein from Olea europea (olive) leaf extract and antioxidant activitiesView study →}.

Two facts set this molecule apart. First, it is the one olive phenol with a regulatory health claim: the European Food Safety Authority (EFSA) concluded that olive-oil polyphenols protect blood lipids from oxidative damage, at an intake of 5 mg of hydroxytyrosol and its derivatives per day ^{2Reference 2EFSA Panel on Dietetic Products et al. · 2011Scientific Opinion on the substantiation of health claims related to polyphenols in olive and protection of LDL particles from oxidative damage, maintenance of normal blood HDL cholesterol concentrations, maintenance of normal blood pressure, anti-inflammatory properties, contributes to the upper respiratory tract health, can help to maintain a normal function of gastrointestinal tract, and contributes to body defences against external agents pursuant to Article 13(1) of Regulation (EC) No 1924/2006View study →}. That is an olive-oil-polyphenols claim, not an endorsement of a pure-isolate supplement. Second, hydroxytyrosol is not only a food compound — it is also formed endogenously from dopamine, making the same molecule a dietary antioxidant and a human neurotransmitter metabolite ^{4,5Reference 4Rodríguez-Morató J et al. · 2016Metabolic disposition and biological significance of simple phenols of dietary origin: hydroxytyrosol and tyrosolView study →Reference 5Pérez-Mañá C et al. · 2015Ethanol induces hydroxytyrosol formation in humansView study →}. As a constituent of a food eaten for millennia, it carries a reassuring safety profile ^{3,8Reference 3EFSA Panel on Dietetic Products et al. · 2017Safety of hydroxytyrosol as a novel food pursuant to Regulation (EC) No 258/97View study →Reference 8Robles-Almazan M et al. · 2018Hydroxytyrosol: Bioavailability, toxicity, and clinical applicationsView study →}.

The EFSA Health Claim

The single most load-bearing fact about hydroxytyrosol is regulatory: it sits behind the only authorised EU health claim for an olive phenol. In 2011 the EFSA panel concluded there was a cause-and-effect relationship between consumption of olive-oil polyphenols — hydroxytyrosol and its derivatives (the oleuropein complex and tyrosol) — and the protection of LDL particles from oxidative damage ^{2Reference 2EFSA Panel on Dietetic Products et al. · 2011Scientific Opinion on the substantiation of health claims related to polyphenols in olive and protection of LDL particles from oxidative damage, maintenance of normal blood HDL cholesterol concentrations, maintenance of normal blood pressure, anti-inflammatory properties, contributes to the upper respiratory tract health, can help to maintain a normal function of gastrointestinal tract, and contributes to body defences against external agents pursuant to Article 13(1) of Regulation (EC) No 1924/2006View study →}. The authorised claim (Commission Regulation (EU) No 432/2012) reads, in effect, that olive-oil polyphenols contribute to the protection of blood lipids from oxidative stress.

The claim’s numbers matter, and they are easy to misread:

• The beneficial effect is obtained at a daily intake of 5 mg of hydroxytyrosol and its derivatives (e.g. as oleuropein complex and tyrosol) ^{2Reference 2EFSA Panel on Dietetic Products et al. · 2011Scientific Opinion on the substantiation of health claims related to polyphenols in olive and protection of LDL particles from oxidative damage, maintenance of normal blood HDL cholesterol concentrations, maintenance of normal blood pressure, anti-inflammatory properties, contributes to the upper respiratory tract health, can help to maintain a normal function of gastrointestinal tract, and contributes to body defences against external agents pursuant to Article 13(1) of Regulation (EC) No 1924/2006View study →}.
• In practice this means a qualifying olive oil must contain at least ~250 mg/kg of those phenols (≈ 5 mg per 20 g of oil) — so the claim is carried by everyday consumption of a phenol-rich virgin oil ^{2Reference 2EFSA Panel on Dietetic Products et al. · 2011Scientific Opinion on the substantiation of health claims related to polyphenols in olive and protection of LDL particles from oxidative damage, maintenance of normal blood HDL cholesterol concentrations, maintenance of normal blood pressure, anti-inflammatory properties, contributes to the upper respiratory tract health, can help to maintain a normal function of gastrointestinal tract, and contributes to body defences against external agents pursuant to Article 13(1) of Regulation (EC) No 1924/2006View study →}.
• The human evidence EFSA relied on was a set of controlled olive-oil feeding studies — chiefly the EUROLIVE trial — showing that the oil’s phenolic content dose-dependently lowered oxidised LDL in blood ^{1Reference 1Covas MI et al. · 2006RCTThe effect of polyphenols in olive oil on heart disease risk factors: a randomized trialView study →}.

The crucial nuance: this is an olive-oil-polyphenols claim, not a pure-hydroxytyrosol supplement claim. It was substantiated on whole virgin olive oil delivering hydroxytyrosol plus its derivatives, and it does not license marketing an isolated hydroxytyrosol capsule as protecting the heart. Read it as the strongest human signal for the molecule’s antioxidant role — anchored in a food matrix, not in the isolate ^{1,2Reference 1Covas MI et al. · 2006RCTThe effect of polyphenols in olive oil on heart disease risk factors: a randomized trialView study →Reference 2EFSA Panel on Dietetic Products et al. · 2011Scientific Opinion on the substantiation of health claims related to polyphenols in olive and protection of LDL particles from oxidative damage, maintenance of normal blood HDL cholesterol concentrations, maintenance of normal blood pressure, anti-inflammatory properties, contributes to the upper respiratory tract health, can help to maintain a normal function of gastrointestinal tract, and contributes to body defences against external agents pursuant to Article 13(1) of Regulation (EC) No 1924/2006View study →}.

Hydroxytyrosol & Oleuropein

Hydroxytyrosol and oleuropein are two ends of the same chemistry. Oleuropein is hydroxytyrosol esterified to elenolic acid and carrying a glucose unit; break those bonds and you liberate hydroxytyrosol, the catechol that does much of the antioxidant work ^{15Reference 15Yuan JJ et al. · 2015Enzymatic hydrolysis of oleuropein from Olea europea (olive) leaf extract and antioxidant activitiesView study →}. Because oleuropein is a large, polar glycoside that is poorly absorbed intact, what a body actually circulates after eating olive products is largely hydroxytyrosol and its conjugates, not the parent glycoside — so “oleuropein activity” in vivo is substantially hydroxytyrosol activity ^{6Reference 6de Bock M et al. · 2013Human absorption and metabolism of oleuropein and hydroxytyrosol ingested as olive (Olea europaea L.) leaf extractView study →}.

This hydrolysis is also the chemistry of the olive itself. A fresh olive is bitter because it is loaded with oleuropein; ripening, table-olive curing and fermentation hydrolyse that oleuropein away, and in naturally-fermented green olives it is the fruit’s own endogenous β-glucosidase and esterase that do the conversion ^{16Reference 16Ramírez E et al. · 2016Oleuropein hydrolysis in natural green olives: importance of the endogenous enzymesView study →}. Enzymatic hydrolysis of olive-leaf oleuropein can convert nearly all of it (~98%) to hydroxytyrosol in vitro ^{15Reference 15Yuan JJ et al. · 2015Enzymatic hydrolysis of oleuropein from Olea europea (olive) leaf extract and antioxidant activitiesView study →}. The practical consequence is a see-saw: processed and stored olive products tend to be lower in oleuropein and correspondingly richer in hydroxytyrosol than the fresh leaf or fruit.

The same secoiridoid family gives rise to hydroxytyrosol’s chemical relatives in the olive — tyrosol (its mono-phenol analogue, lacking the second hydroxyl and much of the antioxidant punch), and the dialdehyde secoiridoids oleocanthal and oleacein. Oleacein in particular is essentially the secoiridoid-aldehyde built on a hydroxytyrosol core, which is why olive oil’s phenol fraction behaves as an interlocking set rather than a single active ^{2Reference 2EFSA Panel on Dietetic Products et al. · 2011Scientific Opinion on the substantiation of health claims related to polyphenols in olive and protection of LDL particles from oxidative damage, maintenance of normal blood HDL cholesterol concentrations, maintenance of normal blood pressure, anti-inflammatory properties, contributes to the upper respiratory tract health, can help to maintain a normal function of gastrointestinal tract, and contributes to body defences against external agents pursuant to Article 13(1) of Regulation (EC) No 1924/2006View study →}.

An Endogenous Dopamine Metabolite

A distinctive fact separates hydroxytyrosol from most dietary phenols: the body makes it too. Hydroxytyrosol is chemically identical to 3,4-dihydroxyphenylethanol (DOPET), a minor endogenous metabolite of dopamine ^{4Reference 4Rodríguez-Morató J et al. · 2016Metabolic disposition and biological significance of simple phenols of dietary origin: hydroxytyrosol and tyrosolView study →}. In the reductive arm of dopamine catabolism, the reactive catechol-aldehyde DOPAL is reduced (by aldehyde/aldose reductases) to DOPET/hydroxytyrosol, in parallel with the better-known oxidation of DOPAL to DOPAC ^{4Reference 4Rodríguez-Morató J et al. · 2016Metabolic disposition and biological significance of simple phenols of dietary origin: hydroxytyrosol and tyrosolView study →}.

This is not merely a chemical curiosity. Endogenous hydroxytyrosol formation is measurable and modifiable in humans: controlled dosing of ethanol shifts dopamine metabolism toward the reductive route, raising endogenous hydroxytyrosol and lowering the DOPAC/hydroxytyrosol ratio in a dose-dependent way ^{5Reference 5Pérez-Mañá C et al. · 2015Ethanol induces hydroxytyrosol formation in humansView study →}. The overlap has two implications the reader should hold onto: (1) background hydroxytyrosol is present in people who have never touched olive oil, complicating any attempt to read a plasma level as purely dietary ^{4Reference 4Rodríguez-Morató J et al. · 2016Metabolic disposition and biological significance of simple phenols of dietary origin: hydroxytyrosol and tyrosolView study →}; and (2) it gives a mechanistic thread to the molecule’s much-studied but still-preclinical neuroprotective chemistry, since a dopamine-derived antioxidant is well placed to buffer the oxidative and quinone stress of dopaminergic neurons ^{4,10Reference 4Rodríguez-Morató J et al. · 2016Metabolic disposition and biological significance of simple phenols of dietary origin: hydroxytyrosol and tyrosolView study →Reference 10Yu G et al. · 2016Hydroxytyrosol induces phase II detoxifying enzyme expression and effectively protects dopaminergic cells against dopamine- and 6-hydroxydopamine induced cytotoxicityView study →}.

What It's Used For

Hydroxytyrosol’s evidence base is broad but stratified by evidence tier: a genuine human antioxidant/LDL signal anchored in the olive-oil matrix, a smaller set of human supplement trials (usually multi-ingredient), and an extensive preclinical profile for the isolate in cells and animals.

Evidence by IndicationStrength of support · Beta

Support is an experimental score — weighted by study type (human > animal > in vitro) and volume. A beta, not a validated metric. The top row is the olive-oil result behind the EFSA claim; the supplement rows are often multi-ingredient. Read the per-row basis.

01Antioxidant / LDL protectionPromising56%Controlled olive-oil trials (↓ oxidised LDL) + the EFSA claim ^{1,2Reference 1Covas MI et al. · 2006RCTThe effect of polyphenols in olive oil on heart disease risk factors: a randomized trialView study →Reference 2EFSA Panel on Dietetic Products et al. · 2011Scientific Opinion on the substantiation of health claims related to polyphenols in olive and protection of LDL particles from oxidative damage, maintenance of normal blood HDL cholesterol concentrations, maintenance of normal blood pressure, anti-inflammatory properties, contributes to the upper respiratory tract health, can help to maintain a normal function of gastrointestinal tract, and contributes to body defences against external agents pursuant to Article 13(1) of Regulation (EC) No 1924/2006View study →}

02Cardiovascular / endothelialPromising46%Human RCTs of HT-containing supplements: endothelial function, BP, oxLDL ^{13,14Reference 13Quirós-Fernández R et al. · 2019RCTSupplementation with hydroxytyrosol and punicalagin improves early atherosclerosis markers involved in the asymptomatic phase of atherosclerosis in the adult population: a randomized, placebo-controlled, crossover trialView study →Reference 14Colica C et al. · 2017RCTAntioxidant effects of a hydroxytyrosol-based pharmaceutical formulation on body composition, metabolic state, and gene expression: a randomized double-blinded, placebo-controlled crossover trialView study →}

03NeuroprotectiveShaky36%Isolate ↑ Nrf2/phase-II + mitochondrial biogenesis; protects dopaminergic/retinal cells ^{9,10Reference 9Zhu L et al. · 2010Hydroxytyrosol protects against oxidative damage by simultaneous activation of mitochondrial biogenesis and phase II detoxifying enzyme systems in retinal pigment epithelial cellsView study →Reference 10Yu G et al. · 2016Hydroxytyrosol induces phase II detoxifying enzyme expression and effectively protects dopaminergic cells against dopamine- and 6-hydroxydopamine induced cytotoxicityView study →}

04Metabolic / glycaemicShaky34%Human HT-formulation crossover + α-glucosidase/α-amylase inhibition ^{11,14Reference 11Hadrich F et al. · 2015The α-glucosidase and α-amylase enzyme inhibitory of hydroxytyrosol and oleuropeinView study →Reference 14Colica C et al. · 2017RCTAntioxidant effects of a hydroxytyrosol-based pharmaceutical formulation on body composition, metabolic state, and gene expression: a randomized double-blinded, placebo-controlled crossover trialView study →}

05Anti-inflammatoryShaky30%Isolate ↓ inflammatory/oxidative signalling; review-level ^{8,10Reference 8Robles-Almazan M et al. · 2018Hydroxytyrosol: Bioavailability, toxicity, and clinical applicationsView study →Reference 10Yu G et al. · 2016Hydroxytyrosol induces phase II detoxifying enzyme expression and effectively protects dopaminergic cells against dopamine- and 6-hydroxydopamine induced cytotoxicityView study →}

06AntimicrobialShaky24%In-vitro antibacterial (hydroxytyrosol broader than oleuropein) ^{12Reference 12Bisignano G et al. · 1999On the in-vitro antimicrobial activity of oleuropein and hydroxytyrosolView study →}

Mechanisms

The load-bearing subtlety is that hydroxytyrosol acts on two levels at once — a direct catechol radical-scavenger and an inducer of the cell’s own antioxidant machinery (Nrf2/phase-II, mitochondrial biogenesis) — which is why its protective effects persist beyond the brief window its free-phenol plasma levels would predict ^{9,10Reference 9Zhu L et al. · 2010Hydroxytyrosol protects against oxidative damage by simultaneous activation of mitochondrial biogenesis and phase II detoxifying enzyme systems in retinal pigment epithelial cellsView study →Reference 10Yu G et al. · 2016Hydroxytyrosol induces phase II detoxifying enzyme expression and effectively protects dopaminergic cells against dopamine- and 6-hydroxydopamine induced cytotoxicityView study →}.

Pharmacokinetics

Hydroxytyrosol is a small, water-and-lipid-compatible phenol, and unlike its parent glycoside it is well absorbed — a large fraction of an oral dose is taken up. Its defining PK fact is rapid, extensive first-pass conjugation: it is converted to hydroxytyrosol sulfate and glucuronides (and related catechol metabolites such as homovanillic alcohol), so free hydroxytyrosol in plasma is low and short-lived while conjugates dominate ^{6,7Reference 6de Bock M et al. · 2013Human absorption and metabolism of oleuropein and hydroxytyrosol ingested as olive (Olea europaea L.) leaf extractView study →Reference 7Alemán-Jiménez C et al. · 2021Pharmacokinetics and bioavailability of hydroxytyrosol are dependent on the food matrix in humansView study →}. Absorption is strongly food-matrix dependent — the same 5 mg dose gives higher plasma hydroxytyrosol and urinary recovery from an olive-oil matrix than from water or an aqueous vehicle, which is one reason the EFSA claim is framed around oil ^{7Reference 7Alemán-Jiménez C et al. · 2021Pharmacokinetics and bioavailability of hydroxytyrosol are dependent on the food matrix in humansView study →}. When ingested as oleuropein or olive-leaf extract, most of the absorbed and circulating species are hydroxytyrosol and its conjugates rather than the intact glycoside — hydroxytyrosol is effectively the delivered active ^{6Reference 6de Bock M et al. · 2013Human absorption and metabolism of oleuropein and hydroxytyrosol ingested as olive (Olea europaea L.) leaf extractView study →}. Complicating any measurement, there is a real endogenous background from dopamine metabolism that adds to the dietary signal ^{4,5Reference 4Rodríguez-Morató J et al. · 2016Metabolic disposition and biological significance of simple phenols of dietary origin: hydroxytyrosol and tyrosolView study →Reference 5Pérez-Mañá C et al. · 2015Ethanol induces hydroxytyrosol formation in humansView study →}.

Clinical Trials

Human evidence is olive-oil-based for the antioxidant claim and small/multi-ingredient for supplements. Controlled olive-oil feeding trials underpin the EFSA lipid-oxidation claim ^{1,2Reference 1Covas MI et al. · 2006RCTThe effect of polyphenols in olive oil on heart disease risk factors: a randomized trialView study →Reference 2EFSA Panel on Dietetic Products et al. · 2011Scientific Opinion on the substantiation of health claims related to polyphenols in olive and protection of LDL particles from oxidative damage, maintenance of normal blood HDL cholesterol concentrations, maintenance of normal blood pressure, anti-inflammatory properties, contributes to the upper respiratory tract health, can help to maintain a normal function of gastrointestinal tract, and contributes to body defences against external agents pursuant to Article 13(1) of Regulation (EC) No 1924/2006View study →}; randomised trials of hydroxytyrosol-containing supplements report vascular and metabolic effects, usually as formulations rather than the isolate ^{13,14Reference 13Quirós-Fernández R et al. · 2019RCTSupplementation with hydroxytyrosol and punicalagin improves early atherosclerosis markers involved in the asymptomatic phase of atherosclerosis in the adult population: a randomized, placebo-controlled, crossover trialView study →Reference 14Colica C et al. · 2017RCTAntioxidant effects of a hydroxytyrosol-based pharmaceutical formulation on body composition, metabolic state, and gene expression: a randomized double-blinded, placebo-controlled crossover trialView study →}. There are no large controlled efficacy trials of isolated hydroxytyrosol as a drug.

Last checked: July 2026.

Isolate vs. Plant Studies

Hydroxytyrosol inverts the usual caveat in an interesting way. Its marquee human evidence is neither pure isolate nor whole herb but a food: virgin olive oil, whose phenolic content lowered oxidised LDL and earned the EFSA claim for hydroxytyrosol-and-derivatives ^{1,2Reference 1Covas MI et al. · 2006RCTThe effect of polyphenols in olive oil on heart disease risk factors: a randomized trialView study →Reference 2EFSA Panel on Dietetic Products et al. · 2011Scientific Opinion on the substantiation of health claims related to polyphenols in olive and protection of LDL particles from oxidative damage, maintenance of normal blood HDL cholesterol concentrations, maintenance of normal blood pressure, anti-inflammatory properties, contributes to the upper respiratory tract health, can help to maintain a normal function of gastrointestinal tract, and contributes to body defences against external agents pursuant to Article 13(1) of Regulation (EC) No 1924/2006View study →}. That is a genuine human signal, but it belongs to the oil matrix delivering hydroxytyrosol alongside tyrosol and the oleuropein complex — not to a hydroxytyrosol tablet.

The supplement human evidence exists but is thin and usually multi-ingredient: the endothelial/BP/oxLDL trial paired hydroxytyrosol with punicalagin ^{13Reference 13Quirós-Fernández R et al. · 2019RCTSupplementation with hydroxytyrosol and punicalagin improves early atherosclerosis markers involved in the asymptomatic phase of atherosclerosis in the adult population: a randomized, placebo-controlled, crossover trialView study →}, and the metabolic crossover used a hydroxytyrosol formulation ^{14Reference 14Colica C et al. · 2017RCTAntioxidant effects of a hydroxytyrosol-based pharmaceutical formulation on body composition, metabolic state, and gene expression: a randomized double-blinded, placebo-controlled crossover trialView study →}. The isolated-molecule evidence — the potent radical scavenging, Nrf2/phase-II induction, mitochondrial biogenesis, dopaminergic and retinal protection, enzyme inhibition and antibacterial activity — is overwhelmingly cell and animal work ^{9,10,11,12Reference 9Zhu L et al. · 2010Hydroxytyrosol protects against oxidative damage by simultaneous activation of mitochondrial biogenesis and phase II detoxifying enzyme systems in retinal pigment epithelial cellsView study →Reference 10Yu G et al. · 2016Hydroxytyrosol induces phase II detoxifying enzyme expression and effectively protects dopaminergic cells against dopamine- and 6-hydroxydopamine induced cytotoxicityView study →Reference 11Hadrich F et al. · 2015The α-glucosidase and α-amylase enzyme inhibitory of hydroxytyrosol and oleuropeinView study →Reference 12Bisignano G et al. · 1999On the in-vitro antimicrobial activity of oleuropein and hydroxytyrosolView study →}. The honest framing: a real human antioxidant signal in the olive-oil matrix + a broad preclinical profile for the isolate, connected through the shared olive chemistry and hydroxytyrosol’s role as oleuropein’s absorbed metabolite ^{6,15Reference 6de Bock M et al. · 2013Human absorption and metabolism of oleuropein and hydroxytyrosol ingested as olive (Olea europaea L.) leaf extractView study →Reference 15Yuan JJ et al. · 2015Enzymatic hydrolysis of oleuropein from Olea europea (olive) leaf extract and antioxidant activitiesView study →}.

Its Role in Plants

In the olive, hydroxytyrosol is best understood as a product of secoiridoid metabolism rather than a primary stored end-product. It is the phenylethanoid released when the plant’s dominant secoiridoid, oleuropein, is hydrolysed by its own β-glucosidase and esterase enzymes — a reaction triggered by tissue damage, ripening and processing ^{16Reference 16Ramírez E et al. · 2016Oleuropein hydrolysis in natural green olives: importance of the endogenous enzymesView study →}. The liberated hydroxytyrosol (and the reactive aldehydes freed alongside it) contributes to the olive’s chemical defence against herbivores and microbes, and the fruit’s shift from oleuropein-rich and bitter toward hydroxytyrosol-rich and mild is the biochemical signature of ripening and curing ^{16Reference 16Ramírez E et al. · 2016Oleuropein hydrolysis in natural green olives: importance of the endogenous enzymesView study →}.

Because this conversion also happens in the olive-mill stream, hydroxytyrosol ends up concentrated in olive-mill wastewater — a pollution problem turned raw material, and now a major industrial source of the compound.

Prevalence in Nature

Hydroxytyrosol is, above all, a marker of the olive (Olea europaea) and its products. As the free phenol it is present at relatively low levels in fresh olives and fresh virgin oil, but it is the dominant simple phenol of olive products once secoiridoid hydrolysis has run its course ^{15,16Reference 15Yuan JJ et al. · 2015Enzymatic hydrolysis of oleuropein from Olea europea (olive) leaf extract and antioxidant activitiesView study →Reference 16Ramírez E et al. · 2016Oleuropein hydrolysis in natural green olives: importance of the endogenous enzymesView study →}. Its concentration therefore tracks processing history more than plant part:

• Virgin olive oil — hydroxytyrosol plus its derivatives. Qualifying oils under the EFSA claim carry ≥ ~250 mg/kg (≈ 5 mg per 20 g), with phenol-rich oils higher; free hydroxytyrosol rises during oil storage as bound forms hydrolyse ^{1,2Reference 1Covas MI et al. · 2006RCTThe effect of polyphenols in olive oil on heart disease risk factors: a randomized trialView study →Reference 2EFSA Panel on Dietetic Products et al. · 2011Scientific Opinion on the substantiation of health claims related to polyphenols in olive and protection of LDL particles from oxidative damage, maintenance of normal blood HDL cholesterol concentrations, maintenance of normal blood pressure, anti-inflammatory properties, contributes to the upper respiratory tract health, can help to maintain a normal function of gastrointestinal tract, and contributes to body defences against external agents pursuant to Article 13(1) of Regulation (EC) No 1924/2006View study →}.
• Table olives and ripe fruit — hydroxytyrosol accumulates during ripening, fermentation and curing as oleuropein is hydrolysed away, so processed olives are comparatively hydroxytyrosol-rich ^{16Reference 16Ramírez E et al. · 2016Oleuropein hydrolysis in natural green olives: importance of the endogenous enzymesView study →}.
• Olive leaf — hydroxytyrosol is present and increases as leaf oleuropein hydrolyses during storage and extraction; enzymatic conversion of leaf oleuropein yields hydroxytyrosol near-quantitatively ^{15Reference 15Yuan JJ et al. · 2015Enzymatic hydrolysis of oleuropein from Olea europea (olive) leaf extract and antioxidant activitiesView study →}.
• Olive-mill wastewater — a hydroxytyrosol-rich by-product exploited for commercial recovery ^{16Reference 16Ramírez E et al. · 2016Oleuropein hydrolysis in natural green olives: importance of the endogenous enzymesView study →}.

Beyond the olive, the same molecule occurs endogenously in humans as the dopamine metabolite DOPET, so it is not strictly a plant-only compound ^{4,5Reference 4Rodríguez-Morató J et al. · 2016Metabolic disposition and biological significance of simple phenols of dietary origin: hydroxytyrosol and tyrosolView study →Reference 5Pérez-Mañá C et al. · 2015Ethanol induces hydroxytyrosol formation in humansView study →}.

Major Natural Sources

Source	Plant part / matrix	Reported hydroxytyrosol
Virgin olive oil (Olea europaea)	oil	≥ ~250 mg/kg HT + derivatives in qualifying oils (rises on storage)
Table olives / ripe fruit (Olea europaea)	processed fruit	high; accumulates as oleuropein hydrolyses on curing
Olive leaf (Olea europaea)	leaf	present; rises as leaf oleuropein hydrolyses
Olive-mill wastewater	processing by-product	rich (industrial recovery source)

Figures depend heavily on cultivar, ripeness, processing and storage; the free-phenol level is a moving target that rises as bound secoiridoids break down ^{1,15,16Reference 1Covas MI et al. · 2006RCTThe effect of polyphenols in olive oil on heart disease risk factors: a randomized trialView study →Reference 15Yuan JJ et al. · 2015Enzymatic hydrolysis of oleuropein from Olea europea (olive) leaf extract and antioxidant activitiesView study →Reference 16Ramírez E et al. · 2016Oleuropein hydrolysis in natural green olives: importance of the endogenous enzymesView study →}.

Discovery & Synthesis

Unlike a molecule with a single datable isolation, hydroxytyrosol entered science through two doors at once. In olive chemistry it was long characterised as the catechol hydrolysis product of oleuropein — the phenol left when the olive’s bitter glycoside is cleaved — rather than being credited to one isolation event ^{15,16Reference 15Yuan JJ et al. · 2015Enzymatic hydrolysis of oleuropein from Olea europea (olive) leaf extract and antioxidant activitiesView study →Reference 16Ramírez E et al. · 2016Oleuropein hydrolysis in natural green olives: importance of the endogenous enzymesView study →}. Independently, in neurochemistry, the identical molecule 3,4-dihydroxyphenylethanol (DOPET) was recognised as a minor endogenous metabolite of dopamine ^{4Reference 4Rodríguez-Morató J et al. · 2016Metabolic disposition and biological significance of simple phenols of dietary origin: hydroxytyrosol and tyrosolView study →}. The convergence of the food phenol and the dopamine metabolite on the same structure is part of what makes it distinctive.

As a simple catechol phenylethanol, hydroxytyrosol is straightforward to prepare and is not dependent on total synthesis for supply. Patents: not yet researched.

Commercial Production

Hydroxytyrosol is produced by several competing routes, reflecting its value as a high-purity antioxidant:

• Recovery from olive-mill wastewater — the hydroxytyrosol-rich effluent of oil production is extracted, turning a disposal problem into feedstock ^{16Reference 16Ramírez E et al. · 2016Oleuropein hydrolysis in natural green olives: importance of the endogenous enzymesView study →}.
• Enzymatic (or acid/thermal) hydrolysis of oleuropein — olive-leaf extract, an abundant pruning by-product, is converted near-quantitatively to hydroxytyrosol; much industrial interest in oleuropein is really in this downstream step to the higher-value phenol ^{15Reference 15Yuan JJ et al. · 2015Enzymatic hydrolysis of oleuropein from Olea europea (olive) leaf extract and antioxidant activitiesView study →}.
• Chemical synthesis / bioconversion — the small catechol is also made synthetically or by microbial bioconversion for pharmaceutical-grade material.

This manufacturing story matters for the page’s honesty: purified hydroxytyrosol on the market is often a made or recovered isolate, whereas the human antioxidant evidence is for the compound as delivered in olive oil ^{1,2Reference 1Covas MI et al. · 2006RCTThe effect of polyphenols in olive oil on heart disease risk factors: a randomized trialView study →Reference 2EFSA Panel on Dietetic Products et al. · 2011Scientific Opinion on the substantiation of health claims related to polyphenols in olive and protection of LDL particles from oxidative damage, maintenance of normal blood HDL cholesterol concentrations, maintenance of normal blood pressure, anti-inflammatory properties, contributes to the upper respiratory tract health, can help to maintain a normal function of gastrointestinal tract, and contributes to body defences against external agents pursuant to Article 13(1) of Regulation (EC) No 1924/2006View study →}.

Toxicity & Safety

Hydroxytyrosol carries a low toxicity flag. It is a constituent of a food humans have eaten for millennia — olives and virgin olive oil — and its safety has been formally assessed. EFSA’s evaluation of hydroxytyrosol as a novel food established a NOAEL of 50 mg/kg body weight per day from a subchronic study and concluded the ingredient is safe at the proposed food-fortification uses, noting that anticipated intakes are in the range of, or below, ordinary exposure from olive oil and olives ^{3Reference 3EFSA Panel on Dietetic Products et al. · 2017Safety of hydroxytyrosol as a novel food pursuant to Regulation (EC) No 258/97View study →}. Review-level toxicology likewise reports no meaningful toxicity across the doses studied ^{8Reference 8Robles-Almazan M et al. · 2018Hydroxytyrosol: Bioavailability, toxicity, and clinical applicationsView study →}. The practical cautions are pharmacological rather than toxicological.

Safety at a Glance

✅ Low / no toxicity

• Low-toxicity food antioxidant. A principal phenol of olive oil and olives with a long dietary history; EFSA set a novel-food NOAEL of 50 mg/kg/day and judged it safe at fortification levels ^{3Reference 3EFSA Panel on Dietetic Products et al. · 2017Safety of hydroxytyrosol as a novel food pursuant to Regulation (EC) No 258/97View study →}.
• Backed by a regulatory claim (as the oil). Olive-oil polyphenols including hydroxytyrosol carry the authorised EU claim for protecting blood lipids from oxidative damage at 5 mg/day ^{2Reference 2EFSA Panel on Dietetic Products et al. · 2011Scientific Opinion on the substantiation of health claims related to polyphenols in olive and protection of LDL particles from oxidative damage, maintenance of normal blood HDL cholesterol concentrations, maintenance of normal blood pressure, anti-inflammatory properties, contributes to the upper respiratory tract health, can help to maintain a normal function of gastrointestinal tract, and contributes to body defences against external agents pursuant to Article 13(1) of Regulation (EC) No 1924/2006View study →}.
• Possible additive blood-pressure lowering. Hydroxytyrosol-containing supplements lowered BP in (pre)hypertensive subgroups — relevant if combined with antihypertensive medication ^{13Reference 13Quirós-Fernández R et al. · 2019RCTSupplementation with hydroxytyrosol and punicalagin improves early atherosclerosis markers involved in the asymptomatic phase of atherosclerosis in the adult population: a randomized, placebo-controlled, crossover trialView study →}.
• Claim ≠ isolate. The human antioxidant evidence is for olive-oil polyphenols (hydroxytyrosol plus derivatives), not a pure-hydroxytyrosol supplement; supplement trials are small and often multi-ingredient ^{1,2,13Reference 1Covas MI et al. · 2006RCTThe effect of polyphenols in olive oil on heart disease risk factors: a randomized trialView study →Reference 2EFSA Panel on Dietetic Products et al. · 2011Scientific Opinion on the substantiation of health claims related to polyphenols in olive and protection of LDL particles from oxidative damage, maintenance of normal blood HDL cholesterol concentrations, maintenance of normal blood pressure, anti-inflammatory properties, contributes to the upper respiratory tract health, can help to maintain a normal function of gastrointestinal tract, and contributes to body defences against external agents pursuant to Article 13(1) of Regulation (EC) No 1924/2006View study →Reference 13Quirós-Fernández R et al. · 2019RCTSupplementation with hydroxytyrosol and punicalagin improves early atherosclerosis markers involved in the asymptomatic phase of atherosclerosis in the adult population: a randomized, placebo-controlled, crossover trialView study →}.
• Endogenous background. Some circulating hydroxytyrosol comes from dopamine metabolism, not diet — worth remembering when interpreting blood/urine levels ^{4,5Reference 4Rodríguez-Morató J et al. · 2016Metabolic disposition and biological significance of simple phenols of dietary origin: hydroxytyrosol and tyrosolView study →Reference 5Pérez-Mañá C et al. · 2015Ethanol induces hydroxytyrosol formation in humansView study →}.

Pregnancy and lactation are per-herb / per-supplement decisions and are not adjudicated on this molecule page; EFSA excluded infants under 36 months and pregnant/breastfeeding women from the novel-food target population as a precaution, but no isolate-specific verdict is issued here ^{3Reference 3EFSA Panel on Dietetic Products et al. · 2017Safety of hydroxytyrosol as a novel food pursuant to Regulation (EC) No 258/97View study →}.

Dosage

There is no single established therapeutic dose for isolated hydroxytyrosol. The load-bearing human figure is regulatory:

The 5 mg/day figure is the intake at which olive-oil polyphenols protect blood lipids from oxidative damage ^{2Reference 2EFSA Panel on Dietetic Products et al. · 2011Scientific Opinion on the substantiation of health claims related to polyphenols in olive and protection of LDL particles from oxidative damage, maintenance of normal blood HDL cholesterol concentrations, maintenance of normal blood pressure, anti-inflammatory properties, contributes to the upper respiratory tract health, can help to maintain a normal function of gastrointestinal tract, and contributes to body defences against external agents pursuant to Article 13(1) of Regulation (EC) No 1924/2006View study →}, and it is delivered by everyday consumption of a phenol-rich virgin oil, not by an isolate. Supplement trials have used roughly 10–15 mg/day, usually in a formulation ^{13,14Reference 13Quirós-Fernández R et al. · 2019RCTSupplementation with hydroxytyrosol and punicalagin improves early atherosclerosis markers involved in the asymptomatic phase of atherosclerosis in the adult population: a randomized, placebo-controlled, crossover trialView study →Reference 14Colica C et al. · 2017RCTAntioxidant effects of a hydroxytyrosol-based pharmaceutical formulation on body composition, metabolic state, and gene expression: a randomized double-blinded, placebo-controlled crossover trialView study →}. These are research and regulatory figures, not a personal recommendation.

References

1. Covas MI, et al. (2006). The effect of polyphenols in olive oil on heart disease risk factors: a randomized trial. Annals of Internal Medicine. https://pubmed.ncbi.nlm.nih.gov/16954359/
2. EFSA Panel on Dietetic Products, Nutrition and Allergies (NDA) (2011). Scientific Opinion on the substantiation of health claims related to polyphenols in olive and protection of LDL particles from oxidative damage, maintenance of normal blood HDL cholesterol concentrations, maintenance of normal blood pressure, anti-inflammatory properties, contributes to the upper respiratory tract health, can help to maintain a normal function of gastrointestinal tract, and contributes to body defences against external agents pursuant to Article 13(1) of Regulation (EC) No 1924/2006. EFSA Journal 9(4):2033. https://doi.org/10.2903/j.efsa.2011.2033
3. EFSA Panel on Dietetic Products, Nutrition and Allergies (NDA) (2017). Safety of hydroxytyrosol as a novel food pursuant to Regulation (EC) No 258/97. EFSA Journal 15(3):4728. https://doi.org/10.2903/j.efsa.2017.4728
4. Rodríguez-Morató J, et al. (2016). Metabolic disposition and biological significance of simple phenols of dietary origin: hydroxytyrosol and tyrosol. Drug Metabolism Reviews. https://pubmed.ncbi.nlm.nih.gov/27186796/
5. Pérez-Mañá C, et al. (2015). Ethanol induces hydroxytyrosol formation in humans. Pharmacological Research. https://pubmed.ncbi.nlm.nih.gov/25801942/
6. de Bock M, et al. (2013). Human absorption and metabolism of oleuropein and hydroxytyrosol ingested as olive (Olea europaea L.) leaf extract. Molecular Nutrition & Food Research. https://pubmed.ncbi.nlm.nih.gov/23766098/
7. Alemán-Jiménez C, et al. (2021). Pharmacokinetics and bioavailability of hydroxytyrosol are dependent on the food matrix in humans. European Journal of Nutrition. https://pubmed.ncbi.nlm.nih.gov/32524230/
8. Robles-Almazan M, et al. (2018). Hydroxytyrosol: Bioavailability, toxicity, and clinical applications. Food Research International. https://doi.org/10.1016/j.foodres.2017.11.053
9. Zhu L, et al. (2010). Hydroxytyrosol protects against oxidative damage by simultaneous activation of mitochondrial biogenesis and phase II detoxifying enzyme systems in retinal pigment epithelial cells. Journal of Nutritional Biochemistry. https://pubmed.ncbi.nlm.nih.gov/20149621/
10. Yu G, et al. (2016). Hydroxytyrosol induces phase II detoxifying enzyme expression and effectively protects dopaminergic cells against dopamine- and 6-hydroxydopamine induced cytotoxicity. Neurochemistry International. https://pubmed.ncbi.nlm.nih.gov/26970393/
11. Hadrich F, et al. (2015). The α-glucosidase and α-amylase enzyme inhibitory of hydroxytyrosol and oleuropein. Journal of Oleo Science. https://pubmed.ncbi.nlm.nih.gov/26235001/
12. Bisignano G, et al. (1999). On the in-vitro antimicrobial activity of oleuropein and hydroxytyrosol. Journal of Pharmacy and Pharmacology. https://pubmed.ncbi.nlm.nih.gov/10504039/
13. Quirós-Fernández R, et al. (2019). Supplementation with hydroxytyrosol and punicalagin improves early atherosclerosis markers involved in the asymptomatic phase of atherosclerosis in the adult population: a randomized, placebo-controlled, crossover trial. Nutrients. https://pubmed.ncbi.nlm.nih.gov/30884808/
14. Colica C, et al. (2017). Antioxidant effects of a hydroxytyrosol-based pharmaceutical formulation on body composition, metabolic state, and gene expression: a randomized double-blinded, placebo-controlled crossover trial. Oxidative Medicine and Cellular Longevity. https://pubmed.ncbi.nlm.nih.gov/28855976/
15. Yuan JJ, et al. (2015). Enzymatic hydrolysis of oleuropein from Olea europea (olive) leaf extract and antioxidant activities. Molecules. https://pubmed.ncbi.nlm.nih.gov/25679050/
16. Ramírez E, et al. (2016). Oleuropein hydrolysis in natural green olives: importance of the endogenous enzymes. Food Chemistry. https://pubmed.ncbi.nlm.nih.gov/27041317/

View all 16 references▾