Horny Goat Weed (Epimedium)
Horny goat weed is the traditional Chinese herb Epimedium, whose principal active flavonoid icariin acts as a weak PDE5 inhibitor. It is used as an aphrodisiac and mild erectile aid. Human clinical data on the whole herb are sparse; the mechanistic rationale rests largely on preclinical PDE5-inhibition work on isolated icariin.
01 Overview
Icariin and related prenylflavonoids inhibit phosphodiesterase-5 in the same broad way as sildenafil, though far more weakly, which supports the herb's traditional erectile-support reputation. Preclinical work also suggests nitric-oxide and mild neurotrophic effects, and some animal studies hint at bone and testosterone-supportive actions, but robust human trials of the whole extract are lacking.
Users take standardised Epimedium extract (icariin percentage stated) for libido and erectile support, sometimes stacked with other botanicals. It is a distinct whole-herb preparation from isolated icariin. Because it has genuine (if weak) PDE5 activity, it can interact dangerously with nitrates and other ED drugs, and stimulatory cardiovascular effects are reported at higher doses.
02 Mechanism
Epimedium flavonoids, chiefly icariin, act as weak PDE5 inhibitors raising cyclic GMP and supporting erectile function, with proposed nitric-oxide and mild hormonal/neurotrophic effects seen mostly in animals.
03 Dosing
| Tier | Dose | Route | Notes |
|---|---|---|---|
| Standardised extract | 250–1000 mg/day | Oral | Extract standardised to ~10-20% icariin; potency varies widely between products. |
| Higher supplemental use | 1000–1500 mg/day | Oral | Upper anecdotal range; cardiovascular stimulation more likely. |
04 Effects
| Effect | Magnitude | Evidence | |
|---|---|---|---|
| Erectile / libido supportTraditional and anecdotal use for erectile function, consistent with weak PDE5 activity; whole-herb human trials are lacking. | subjective | Anecdotal | |
| Weak PDE5 inhibitionIsolated icariin inhibits PDE5 in vitro, the mechanistic basis of the herb's reputation. | much weaker than sildenafil | Preclinical |
05 Side effects
| Effect | Severity | Frequency | Evidence | Countermeasures |
|---|---|---|---|---|
| Cardiovascular stimulationRapid heartbeat, palpitations or dizziness at higher doses. | Moderate | Dose-dependent | Anecdotal | |
| Interaction with nitrates / PDE5 drugsWeak PDE5 activity can add to nitrates or other ED drugs, risking dangerous hypotension. | Severe | Interaction | Observational |