OtherSupplementFlavonoidHerbal PDE5 inhibitor

Icariin

Also known as Horny goat weed extract · Epimedium extract · Yin yang huo

Written by enwyReviewed 5 Aug 20262 sources0 comments

Icariin is a flavonoid extracted from Epimedium ('horny goat weed') and marketed as a natural PDE5 inhibitor for erectile function and libido. It does inhibit PDE5 in vitro, but far more weakly than pharmaceutical agents, and human evidence is minimal — the supporting data are overwhelmingly preclinical, with concern that some 'icariin' products are spiked with real PDE5 drugs.

01 Overview

Icariin is the principal active flavonoid of Epimedium species and has demonstrable but weak PDE5-inhibitory activity in laboratory studies, along with antioxidant and possible neuroprotective effects in animal models. This is the basis for its traditional and supplement use for erectile function and libido.

Human clinical evidence is very limited, and its in-vitro PDE5 potency is orders of magnitude below sildenafil, so realistic supplement doses are unlikely to reproduce a drug-like effect. A recurring real-world hazard is adulteration: 'natural' Epimedium/icariin products have repeatedly been found spiked with undeclared sildenafil or analogues, which carries the same nitrate-interaction danger as the drugs themselves without the labelling.

02 Mechanism

Flavonoid with weak in-vitro PDE5-inhibitory activity plus antioxidant/neuroprotective effects in preclinical models; clinical relevance at supplement doses is unproven.

03 Dosing

Tier	Dose	Route	Notes
Supplement (extract)	250–1000 mg/day	Oral	Typical standardised-extract dosing; actual icariin content and effect vary widely by product.

04 Effects

Effect	Magnitude	Evidence
Weak PDE5 inhibition / libidoIn-vitro PDE5 inhibition and animal data suggest erectile/libido effects, but far weaker than pharmaceutical PDE5 inhibitors.	weak	Preclinical

05 Side effects

Effect	Severity	Frequency	Evidence	Countermeasures
Mild GI upset / dizzinessOccasional stomach upset, dizziness or dry mouth reported.	Mild	Uncommon	Anecdotal
Adulteration with undeclared PDE5 drugsHerbal 'sexual enhancement' products including Epimedium have repeatedly been found spiked with sildenafil/analogues, creating a hidden nitrate-interaction risk.	Severe	Product-dependent	Observational

06 Legal status

United Kingdom

Herbal supplement

as of Jan 2026

United States

Dietary supplement

Sold as a botanical supplement; individual products may be adulterated and subject to FDA action. · as of Jan 2026

07 References

Icariin as a PDE5 inhibitor: in-vitro and preclinical evidenceAsian J Androl

FDA warnings on undeclared sildenafil in sexual-enhancement supplementsUS FDA

08 Discussion0 comments

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This page is reference information, not medical advice. Doses and protocols are documented as they appear in the clinical literature and in practice — describing them is not a recommendation to use them. Countermeasures listed here are not a substitute for a physician. Legal status varies by jurisdiction and changes.