Chrysin

Pharmacology & Research

Chrysin (5,7-dihydroxyflavone) is a flavone from honey, propolis and passionflower, best known as a bodybuilding supplement sold as a “natural aromatase inhibitor” or testosterone booster. That reputation has a real root and a decisive flaw. The root: chrysin is a genuinely potent aromatase (CYP19) inhibitor in the test tube, among the more potent dietary flavones tested ^{3Reference 3Kao YC et al. · 1998Molecular basis of the inhibition of human aromatase (estrogen synthetase) by flavone and isoflavone phytoestrogensView study →}. The flaw: in humans it does nothing to hormones, because oral chrysin is almost entirely destroyed by first-pass conjugation before it reaches the bloodstream — its oral bioavailability is under ~1% ^{1Reference 1Walle T et al. · 2001Disposition and metabolism of the flavonoid chrysin in normal volunteersView study →}, and a controlled trial found no change in testosterone ^{2Reference 2Gambelunghe C et al. · 2003Effects of chrysin on urinary testosterone levels in human malesView study →}. Its other, better-founded pharmacology is preclinical and CNS-flavoured: chrysin binds the GABA-A benzodiazepine site and is anxiolytic in rodents ^{4Reference 4Wolfman C et al. · 1994Possible anxiolytic effects of chrysin, a central benzodiazepine-receptor ligand isolated from Passiflora coeruleaView study →}, the mechanistic backbone of passionflower’s traditional sedative use.

1. Anxiolytic / CNS

Chrysin displaces benzodiazepine ligands at the central GABA-A benzodiazepine site and is anxiolytic in the elevated plus-maze in mice — an effect blocked by flumazenil, a clean receptor-level demonstration ^{4Reference 4Wolfman C et al. · 1994Possible anxiolytic effects of chrysin, a central benzodiazepine-receptor ligand isolated from Passiflora coeruleaView study →} — reproduced in rats with a Passiflora extract ^{5Reference 5Brown E et al. · 2007AnimalEvaluation of the anxiolytic effects of chrysin, a Passiflora incarnata extract, in the laboratory ratView study →}, and extended to an antidepressant-like effect (with raised BDNF/NGF) in chronic-mild-stress models ^{6,7Reference 6Filho CB et al. · 2015Chronic unpredictable mild stress decreases BDNF and NGF levels and the antidepressant-like effect of chrysinView study →Reference 7Zanoli P et al. · 2000Behavioural characterisation of the flavonoids apigenin and chrysinView study →}.

Gap: all animal, no human trials, and the injected/high oral doses used bypass the bioavailability problem that sinks the oral supplement story ^{4,5Reference 4Wolfman C et al. · 1994Possible anxiolytic effects of chrysin, a central benzodiazepine-receptor ligand isolated from Passiflora coeruleaView study →Reference 5Brown E et al. · 2007AnimalEvaluation of the anxiolytic effects of chrysin, a Passiflora incarnata extract, in the laboratory ratView study →}.

2. Anti-inflammatory / antioxidant

Chrysin activates the Nrf2/HO-1 antioxidant response and suppresses NF-κB in numerous rodent injury models — for example protecting against cerebral ischemia/reperfusion injury in mice ^{9Reference 9Yao Y et al. · 2014AnimalChrysin protects against focal cerebral ischemia/reperfusion injury in mice through the Nrf2 pathwayView study →} — as aggregated across reviews ^{10Reference 10Mani R · 2018Chrysin: sources, beneficial pharmacological activities and molecular mechanism of actionView study →}.

Gap: preclinical only, with the same bioavailability ceiling, so the effects occur at doses/routes not achievable by oral human dosing ^{9,10Reference 9Yao Y et al. · 2014AnimalChrysin protects against focal cerebral ischemia/reperfusion injury in mice through the Nrf2 pathwayView study →Reference 10Mani R · 2018Chrysin: sources, beneficial pharmacological activities and molecular mechanism of actionView study →}.

3. Anticancer

Chrysin is pro-apoptotic, anti-proliferative and chemosensitising across many cancer cell lines ^{8Reference 8Kasala ER et al. · 2015Chemopreventive and therapeutic potential of chrysin in cancer: mechanistic perspectivesView study →}, and it originally surfaced in a cancer-chemoprevention isolation screen ^{12Reference 12Liu YL et al. · 1992Isolation of potential cancer chemopreventive agents from Eriodictyon californicumView study →}.

Gap: entirely preclinical, with micromolar in-vitro potencies far above achievable human plasma levels and no human oncology data ^{8Reference 8Kasala ER et al. · 2015Chemopreventive and therapeutic potential of chrysin in cancer: mechanistic perspectivesView study →}.

4. Aromatase / “testosterone booster”

The marquee supplement claim, and the central honesty point. Chrysin is a competitive aromatase (CYP19) inhibitor with sub-micromolar potency in vitro — which is exactly why the supplement industry adopted it ^{3Reference 3Kao YC et al. · 1998Molecular basis of the inhibition of human aromatase (estrogen synthetase) by flavone and isoflavone phytoestrogensView study →}. But when tested in men, 21 days of chrysin-containing propolis/honey produced no change in urinary testosterone ^{2Reference 2Gambelunghe C et al. · 2003Effects of chrysin on urinary testosterone levels in human malesView study →}, because oral chrysin essentially never reaches the circulation intact (see Pharmacokinetics).

Gap: no human RCT has ever shown chrysin raises testosterone or lowers estrogen — the claim is an in-vitro-to-marketing leap that fails on pharmacokinetics ^{1,2Reference 1Walle T et al. · 2001Disposition and metabolism of the flavonoid chrysin in normal volunteersView study →Reference 2Gambelunghe C et al. · 2003Effects of chrysin on urinary testosterone levels in human malesView study →}.

5. Metabolic

Chrysin improved glycemia and lipids with anti-inflammatory effects in diabetic rodents, as reviewed ^{10,11Reference 10Mani R · 2018Chrysin: sources, beneficial pharmacological activities and molecular mechanism of actionView study →Reference 11Naz S et al. · 2019Chrysin: pharmacological and therapeutic propertiesView study →}.

Gap: animal-only, with low human relevance absent a delivery fix ^{10,11Reference 10Mani R · 2018Chrysin: sources, beneficial pharmacological activities and molecular mechanism of actionView study →Reference 11Naz S et al. · 2019Chrysin: pharmacological and therapeutic propertiesView study →}.

Mechanisms

Target / pathway	Effect	Relevant to
Aromatase / CYP19 (estrogen synthase)	competitive inhibition, sub-µM Ki in vitro	the hormone claim — but no human effect
GABA-A benzodiazepine site	partial agonist / positive modulator; anxiolytic, flumazenil-reversible (rodent)	anxiolytic, antidepressant-like
Nrf2 / HO-1 (antioxidant response)	↑ HO-1, SOD, catalase; ↓ ROS (rodent)	anti-inflammatory / cytoprotection
NF-κB signalling	suppression → ↓ pro-inflammatory cytokines	anti-inflammatory, anticancer signalling

Pharmacokinetics

This is the load-bearing caveat and the reason the aromatase claim collapses in humans. In the definitive human study, volunteers took a single 400 mg oral dose: peak plasma parent chrysin was only 3–16 ng/mL, chrysin sulfate ran ~30× higher, and most of the dose was recovered unabsorbed in the faeces — an estimated oral bioavailability of ~0.003–1% ^{1Reference 1Walle T et al. · 2001Disposition and metabolism of the flavonoid chrysin in normal volunteersView study →}. The cause is extensive first-pass glucuronidation and sulfation in both gut wall and liver, plus efflux of conjugates back into the intestine ^{1,10Reference 1Walle T et al. · 2001Disposition and metabolism of the flavonoid chrysin in normal volunteersView study →Reference 10Mani R · 2018Chrysin: sources, beneficial pharmacological activities and molecular mechanism of actionView study →}. The consequence: the potent in-vitro aromatase inhibition is pharmacologically inaccessible by oral dosing, because systemic parent-drug exposure sits far below any concentration active on CYP19 or GABA-A. Marketed products often add piperine to try to overcome this, but no human efficacy data exist for those combinations.

Clinical trials

Human data are thin and negative for the headline claim: a 21-day study of chrysin-containing propolis/honey found no change in urinary testosterone in men ^{2Reference 2Gambelunghe C et al. · 2003Effects of chrysin on urinary testosterone levels in human malesView study →}, and the only other human study is the pharmacokinetic disposition trial documenting near-absent bioavailability ^{1Reference 1Walle T et al. · 2001Disposition and metabolism of the flavonoid chrysin in normal volunteersView study →}. There are no RCTs for anxiety, inflammation, cancer or metabolic endpoints — all therapeutic evidence is preclinical.

Last checked: July 2026.

Toxicity & Safety

Chrysin has low apparent oral toxicity: single or short-term oral doses (up to 400 mg, and customary propolis/honey regimens) were tolerated without reported adverse events ^{1,2Reference 1Walle T et al. · 2001Disposition and metabolism of the flavonoid chrysin in normal volunteersView study →Reference 2Gambelunghe C et al. · 2003Effects of chrysin on urinary testosterone levels in human malesView study →}, and its own poor absorption limits systemic exposure and therefore systemic toxicity. The more substantive concern is a drug-interaction signal: chrysin strongly modulates conjugation enzymes, competing at UGT (glucuronidation) and SULT (sulfation) pathways and inducing intestinal UGT1A1 in vitro ^{1,10Reference 1Walle T et al. · 2001Disposition and metabolism of the flavonoid chrysin in normal volunteersView study →Reference 10Mani R · 2018Chrysin: sources, beneficial pharmacological activities and molecular mechanism of actionView study →}. That makes interactions with drugs cleared by glucuronidation or sulfation — acetaminophen, raloxifene, irinotecan/SN-38, thyroid hormone, some estrogens — mechanistically plausible, though none are clinically documented, so this is a caution rather than a proven event.

Dosage

Nothing here is a recommendation. Marketed supplement doses are commonly 500–3000 mg/day, frequently in “estrogen-blocker” stacks and often combined with piperine to try to overcome the bioavailability problem — but these doses are not supported by human efficacy data, and higher oral doses do not fix the first-pass conjugation ceiling. For research context, the human pharmacokinetic study used a single 400 mg oral dose ^{1Reference 1Walle T et al. · 2001Disposition and metabolism of the flavonoid chrysin in normal volunteersView study →} and the null hormone study delivered chrysin as propolis/honey at customary intakes ^{2Reference 2Gambelunghe C et al. · 2003Effects of chrysin on urinary testosterone levels in human malesView study →}.

References