Olive Leaf

The olive leaf appears in some of the earliest medical writing of the Mediterranean. The Bible names the leaf as a medicine (Ezekiel 47:12: “the fruit thereof shall be for meat and the leaf thereof for medicine”). The ancient Egyptians used the tree in mummification, and the Greeks treated fevers with olive-leaf preparations ^{30Reference 30Bone · 2003A Clinical Guide to Blending Liquid Herbs: Herbal Formulations for the Individual Patient}.

The leaf has been used for high blood pressure, angina, coughs and fevers, and as a diuretic, a bitter for the stomach, a liver stimulant and a remedy to bring on menstruation. It was applied to the skin for snakebites and mouth ulcers ^{30Reference 30Bone · 2003A Clinical Guide to Blending Liquid Herbs: Herbal Formulations for the Individual Patient}.

In folk medicine the leaf has also long been used for diabetes ^{9Reference 9de Bock et al. · 2013RCTOlive (Olea europaea L.) leaf polyphenols improve insulin sensitivity in middle-aged overweight men: a randomized, placebo-controlled, crossover trialView study →}.

In an 8-week double-blind trial in stage-1 hypertension, a standardised olive leaf extract (EFLA®943, 500 mg twice daily) lowered systolic blood pressure by 11.5 mmHg, against 13.7 mmHg for captopril 12.5–25 mg twice daily. The difference between the two was not significant ^{1Reference 1Susalit et al. · 2011RCTOlive (Olea europaea) leaf extract effective in patients with stage-1 hypertension: comparison with Captopril — randomised controlled trialView study →}.

In a crossover trial in 60 pre-hypertensive men, a phenolic-rich extract (136 mg oleuropein a day) lowered 24-hour systolic blood pressure by about 3.3 mmHg compared with control ^{2Reference 2Lockyer et al. · 2017RCTImpact of phenolic-rich olive leaf extract on blood pressure, plasma lipids and inflammatory markers: a randomised controlled trialView study →}. In a 2025 multicentre trial of 621 people treated for hypertension, 24-hour systolic pressure fell by 6.4 mmHg from baseline on the extract, against 1.5 mmHg on placebo ^{3Reference 3Lamti et al. · 2025RCTEfficacy of olive leaf extracts in controlling blood pressure in hypertensive patients: a double-blind randomized clinical trial — multicentre RCTView study →}.

In a 2026 trial of extract combined with potassium, morning home systolic pressure fell by 5.4 mmHg ^{4Reference 4Fladerer-Grollitsch et al. · 2026RCTEffects of a combination of olive leaf extract and potassium on blood pressure in participants with mild to moderate hypertension: a double-blind, randomized, placebo-controlled trialView study →}. The 2024 meta-analysis found a favourable effect on blood pressure in two of its twelve trials ^{5Reference 5Álvares et al. · 2024Meta-analysisOlive leaf extract effect on cardiometabolic risk factors: a systematic review and meta-analysis of randomized clinical trialsView study →}.

Not every trial is positive. A combination of olive leaf, green coffee bean and beetroot extracts had no effect on ambulatory blood pressure ^{7Reference 7Wong et al. · 2014RCTAntihypertensive potential of combined extracts of olive leaf, green coffee bean and beetroot: a randomized, double-blind, placebo-controlled crossover trialView study →}, and two other placebo-controlled trials found no change in blood pressure ^{8,9Reference 8Stevens et al. · 2021RCTThe effect of olive leaf extract on cardiovascular health markers: a randomized placebo-controlled clinical trialView study →Reference 9de Bock et al. · 2013RCTOlive (Olea europaea L.) leaf polyphenols improve insulin sensitivity in middle-aged overweight men: a randomized, placebo-controlled, crossover trialView study →}. A combination of citrus and olive extracts lowered systolic and diastolic pressure and improved blood-vessel function in healthy adults ^{29Reference 29Sánchez Macarro et al. · 2020RCTEffect of a combination of citrus flavones and flavanones and olive polyphenols for the reduction of cardiovascular disease risk: an exploratory randomized, double-blind, placebo-controlled study in healthy subjectsView study →}.

Part of the effect is attributed to ACE inhibition. Bioassay-guided fractionation of the water extract of the leaf isolated the secoiridoid oleacein as a strong ACE inhibitor ^{19Reference 19Hansen et al. · 1996In vitroIsolation of an angiotensin converting enzyme (ACE) inhibitor from Olea europaea and Olea lancea — in vitroView study →}.

Effect sizes vary with extract standardisation and starting blood pressure, and no dose-response has been established for the tea or the 1:2 liquid extract.

Several blood-pressure trials measured lipids as secondary outcomes. In the captopril-comparison trial, triglycerides fell on the extract but not on captopril ^{1Reference 1Susalit et al. · 2011RCTOlive (Olea europaea) leaf extract effective in patients with stage-1 hypertension: comparison with Captopril — randomised controlled trialView study →}.

The pre-hypertensive crossover trial found total cholesterol down 0.32 mmol/L, LDL down 0.19 mmol/L and triglycerides down 0.18 mmol/L ^{2Reference 2Lockyer et al. · 2017RCTImpact of phenolic-rich olive leaf extract on blood pressure, plasma lipids and inflammatory markers: a randomised controlled trialView study →}.

The 2026 extract-plus-potassium trial reported total cholesterol down 11.1 mg/dL, LDL down 6.9 mg/dL and triglycerides down about 22 mg/dL at week 6, with oxidised LDL down about 23% ^{4Reference 4Fladerer-Grollitsch et al. · 2026RCTEffects of a combination of olive leaf extract and potassium on blood pressure in participants with mild to moderate hypertension: a double-blind, randomized, placebo-controlled trialView study →}.

The 2024 meta-analysis found a favourable lipid effect in two trials ^{5Reference 5Álvares et al. · 2024Meta-analysisOlive leaf extract effect on cardiometabolic risk factors: a systematic review and meta-analysis of randomized clinical trialsView study →}. The 2026 meta-analysis pooled the parallel-group trials of regular use and found no significant effect on lipids ^{6Reference 6Câmara Rocha Menezes et al. · 2026Meta-analysisMetabolic and inflammatory effects of oleuropein and olive leaf extract: a systematic review and meta-analysisView study →}.

An 8-week trial in 77 overweight or obese adults with mildly raised cholesterol found no significant change in any blood lipid ^{8Reference 8Stevens et al. · 2021RCTThe effect of olive leaf extract on cardiovascular health markers: a randomized placebo-controlled clinical trialView study →}.

Gap: the effect is small and inconsistent, and the one trial that recruited people for raised cholesterol found no change.

In a 12-week trial in 60 people with hypertension, the extract lowered interleukin-6, interleukin-8 and TNF-α compared with placebo ^{10Reference 10Javadi et al. · 2019RCTEffects of olive leaf extract on metabolic response, liver and kidney functions and inflammatory biomarkers in hypertensive patients — randomized controlled trialView study →}.

The pre-hypertensive crossover trial found interleukin-8 fell after the extract ^{2Reference 2Lockyer et al. · 2017RCTImpact of phenolic-rich olive leaf extract on blood pressure, plasma lipids and inflammatory markers: a randomised controlled trialView study →}. In a single-dose crossover trial in 18 healthy volunteers, the extract reduced IL-8 production by blood cells and improved a measure of arterial stiffness ^{11Reference 11Lockyer et al. · 2015RCTSecoiridoids delivered as olive leaf extract induce acute improvements in human vascular function and reduction of an inflammatory cytokine: a randomised, double-blind, placebo-controlled, cross-over trialView study →}.

Results are not uniform. In overweight men, 12 weeks of extract raised fasting interleukin-6 and did not change IL-8 or TNF-α ^{9Reference 9de Bock et al. · 2013RCTOlive (Olea europaea L.) leaf polyphenols improve insulin sensitivity in middle-aged overweight men: a randomized, placebo-controlled, crossover trialView study →}. The 2026 meta-analysis judged the evidence on inflammatory markers scarce and of low certainty ^{6Reference 6Câmara Rocha Menezes et al. · 2026Meta-analysisMetabolic and inflammatory effects of oleuropein and olive leaf extract: a systematic review and meta-analysisView study →}.

In vitro, oleuropein was the only component of the extract that lowered TNF-α release from stimulated white blood cells ^{22Reference 22Qabaha et al. · 2018In vitroOleuropein is responsible for the major anti-inflammatory effects of olive leaf extract — in vitroView study →}.

The clearest human evidence is a 12-week crossover trial in 46 middle-aged overweight men. Olive leaf polyphenols (51 mg oleuropein and about 10 mg hydroxytyrosol a day) improved insulin sensitivity by 15% and pancreatic β-cell responsiveness by 28% compared with placebo ^{9Reference 9de Bock et al. · 2013RCTOlive (Olea europaea L.) leaf polyphenols improve insulin sensitivity in middle-aged overweight men: a randomized, placebo-controlled, crossover trialView study →}.

The large 2025 multicentre trial reported lower blood glucose as a secondary outcome ^{3Reference 3Lamti et al. · 2025RCTEfficacy of olive leaf extracts in controlling blood pressure in hypertensive patients: a double-blind randomized clinical trial — multicentre RCTView study →}. The 2026 extract-plus-potassium trial left fasting glucose and HbA1c unchanged but lowered fasting insulin and the HOMA index ^{4Reference 4Fladerer-Grollitsch et al. · 2026RCTEffects of a combination of olive leaf extract and potassium on blood pressure in participants with mild to moderate hypertension: a double-blind, randomized, placebo-controlled trialView study →}.

Other results point the other way. A hypertension trial found no change in glucose metabolism ^{10Reference 10Javadi et al. · 2019RCTEffects of olive leaf extract on metabolic response, liver and kidney functions and inflammatory biomarkers in hypertensive patients — randomized controlled trialView study →}. In the 2024 meta-analysis, fasting glucose in trials of low extract doses favoured the control group ^{5Reference 5Álvares et al. · 2024Meta-analysisOlive leaf extract effect on cardiometabolic risk factors: a systematic review and meta-analysis of randomized clinical trialsView study →}, and the 2026 meta-analysis found no significant effect on blood sugar across trials of regular use ^{6Reference 6Câmara Rocha Menezes et al. · 2026Meta-analysisMetabolic and inflammatory effects of oleuropein and olive leaf extract: a systematic review and meta-analysisView study →}.

No adequately powered trial exists in people with type 2 diabetes.

In an 8-week trial in 70 women with obesity, adding olive leaf extract (250 mg a day) to a calorie-restricted diet lowered serum malondialdehyde, a marker of fat oxidation, more than diet alone. Total antioxidant capacity and liver enzymes were unchanged ^{12Reference 12Haidari et al. · 2025RCTPhenolic-rich extract of olive leaf with a hypocaloric diet alleviates oxidative stress in obese females: a randomized double-blind placebo-controlled trialView study →}.

In vitro, olive leaf extract scavenges free radicals and protects red blood cells from oxidative damage ^{13Reference 13Lins et al. · 2018In vitroIn vitro antioxidant activity of olive leaf extract (Olea europaea L.) and its protective effect on oxidative damage in human erythrocytes — in vitroView study →}. Hydroxytyrosol, formed when oleuropein breaks down, is itself a strong antioxidant ^{14Reference 14Yuan et al. · 2015In vitroEnzymatic hydrolysis of oleuropein from Olea europea (olive) leaf extract and antioxidant activities — in vitroView study →}.

Most of this is in vitro or on surrogate markers; whether it translates to clinical outcomes is largely untested.

In cholesterol-fed rabbits, olive leaf extract reduced the thickness of atherosclerotic lesions and lowered inflammatory markers, lipids and malondialdehyde ^{15Reference 15Wang et al. · 2008AnimalThe anti-atherosclerotic effect of olive leaf extract is related to suppressed inflammatory response in rabbits with experimental atherosclerosis — animal model (rabbit)View study →}.

In isolated rat hearts, oleuropein limited oxidative damage from ischaemia and reperfusion ^{16Reference 16Manna et al. · 2004AnimalOleuropein prevents oxidative myocardial injury induced by ischemia and reperfusion — animal model (rat)View study →}. In heart-muscle cells it reduced cell death after simulated ischaemia and reperfusion through the reperfusion-injury salvage kinase (RISK) pathway ^{17Reference 17Zhao et al. · 2017In vitroOleuropein protects cardiomyocyte against apoptosis via activating the reperfusion injury salvage kinase pathway in vitroView study →}.

A systematic review of rodent studies found a consistent protective effect on the heart for oleuropein and olive leaf extract ^{18Reference 18Menezes et al. · 2022Systematic reviewOral administration of oleuropein and olive leaf extract has cardioprotective effects in rodents: a systematic review — animalView study →}.

Gap: all of this is animal or cell-based; there are no human trials of clinical cardiac endpoints (infarct size, arrhythmia, mortality).

Olive leaf extract and its main phenolic compounds inhibited Staphylococcus aureus and E. coli in vitro, more strongly S. aureus. With ampicillin, the extract, oleuropein, caffeic acid and verbascoside had an additive effect, and hydroxytyrosol a synergistic one ^{23Reference 23Lim et al. · 2016In vitroPlant phenols as antibiotic boosters: in vitro interaction of olive leaf phenols with ampicillin — in vitroView study →}. In another study, Gram-negative bacteria resisted the extract ^{22Reference 22Qabaha et al. · 2018In vitroOleuropein is responsible for the major anti-inflammatory effects of olive leaf extract — in vitroView study →}.

Against Candida albicans and C. dubliniensis the minimum inhibitory concentrations were high, about 47 and 63 mg/mL ^{24Reference 24Zorić et al. · 2016In vitroOlive leaf extract activity against Candida albicans and C. dubliniensis — the in vitro viability studyView study →}.

In a 2025 trial in 59 people with Candida-related oral disease, adding olive leaf extract to nystatin or miconazole did not lower Candida counts. With nystatin it raised saliva flow, and with miconazole it eased tongue burning ^{26Reference 26Kinkela Devčić et al. · 2025RCTBeneficial effect of olive leaf extract as an adjunct to standard antifungal therapy in treating Candida-related oral diseases — randomized controlled trialView study →}.

Gap: the in-vitro concentrations are far above what oral dosing achieves in tissue, and the one clinical result is as an add-on to antifungal drugs.

In the 5xFAD mouse model of Alzheimer’s disease, an oleuropein-rich olive leaf extract given in the diet at a low dose for three months reduced brain inflammation and amyloid-β, strengthened the blood–brain barrier and improved memory ^{21Reference 21Abdallah et al. · 2022AnimalOleuropein-rich olive leaf extract attenuates neuroinflammation in the Alzheimer’s disease mouse modelView study →}.

No human cognitive or neurological trial of olive leaf exists.

In a 2024 study, olive leaf compounds were docked in silico against several SARS-CoV-2 targets. A standardised extract with 20% oleuropein showed moderate activity against the virus in vitro, with an IC₅₀ of 118 µg/mL ^{27Reference 27Majrashi et al. · 2024In vitroIn vitro biological evaluation and in silico insights into the antiviral activity of standardized olive leaves extract against SARS-CoV-2View study →}.

There are no controlled human antiviral trials. In a 9-week trial in 32 high school athletes, the extract did not change how often they caught an upper respiratory illness, but it cut sick days by 28% ^{25Reference 25Somerville et al. · 2019RCTThe effect of olive leaf extract on upper respiratory illness in high school athletes: a randomised control trialView study →}.

Gap: no clinical antiviral data; in-silico docking and cell assays do not establish efficacy in people.

Isolated oleuropein slows growth and triggers cell death across several cancer cell types in vitro ^{28Reference 28Zheng et al. · 2022ReviewAn updated review on the potential antineoplastic actions of oleuropein — reviewView study →}. No animal efficacy studies of the whole leaf and no human data exist.

Gap: constituent-level, in-vitro evidence only.

Tolerability. Across several 8–12 week trials, including standardised extracts at 500–1,000 mg a day, adverse events were uncommon and similar to placebo. One trial found it as well tolerated as captopril ^{1,3,4Reference 1Susalit et al. · 2011RCTOlive (Olea europaea) leaf extract effective in patients with stage-1 hypertension: comparison with Captopril — randomised controlled trialView study →Reference 3Lamti et al. · 2025RCTEfficacy of olive leaf extracts in controlling blood pressure in hypertensive patients: a double-blind randomized clinical trial — multicentre RCTView study →Reference 4Fladerer-Grollitsch et al. · 2026RCTEffects of a combination of olive leaf extract and potassium on blood pressure in participants with mild to moderate hypertension: a double-blind, randomized, placebo-controlled trialView study →}.

Blood pressure and diabetes medicines. Because olive leaf can lower blood pressure and blood sugar, it may add to the effect of blood-pressure and diabetes medicines ^{3,9,10Reference 3Lamti et al. · 2025RCTEfficacy of olive leaf extracts in controlling blood pressure in hypertensive patients: a double-blind randomized clinical trial — multicentre RCTView study →Reference 9de Bock et al. · 2013RCTOlive (Olea europaea L.) leaf polyphenols improve insulin sensitivity in middle-aged overweight men: a randomized, placebo-controlled, crossover trialView study →Reference 10Javadi et al. · 2019RCTEffects of olive leaf extract on metabolic response, liver and kidney functions and inflammatory biomarkers in hypertensive patients — randomized controlled trialView study →}. It may also lower blood pressure noticeably in people already at or below target ^{1,2,3Reference 1Susalit et al. · 2011RCTOlive (Olea europaea) leaf extract effective in patients with stage-1 hypertension: comparison with Captopril — randomised controlled trialView study →Reference 2Lockyer et al. · 2017RCTImpact of phenolic-rich olive leaf extract on blood pressure, plasma lipids and inflammatory markers: a randomised controlled trialView study →Reference 3Lamti et al. · 2025RCTEfficacy of olive leaf extracts in controlling blood pressure in hypertensive patients: a double-blind randomized clinical trial — multicentre RCTView study →}.

Drug interactions. No human drug-interaction or CYP450 studies have been done, so interactions are inferred from its effects rather than measured.