Horny Goat Weed for Erectile Dysfunction

Horny goat weed (Epimedium, yin yang huo) has not been tested on its own in a published clinical trial in men with erectile dysfunction. A urology review of herbal ED treatments listed Epimedium (icariin) among the herbs studied for ED, but found published human studies only for ginseng, Butea superba and yohimbine [1]. A 2026 review of icariin's effects on ED reached the same point: the benefits are in animal models, and clinical efficacy still needs confirming in high-quality randomised trials [2].

What exists in people is two small trials of multi-ingredient products that contained Epimedium. A 2-week crossover trial of a five-herb product found a slightly larger gain in erectile function than placebo [3][4], and an open-label trial of a six-ingredient preparation reported higher erection scores than with a traditional herbal comparator [5]. Neither can tell you what horny goat weed does by itself, so the verdict is insufficient evidence.

Erections depend on a signalling molecule, cGMP, that relaxes the smooth muscle of the penis; ED drugs such as sildenafil work by blocking PDE5, the enzyme that breaks cGMP down. Icariin, the main flavonoid in horny goat weed, also inhibits PDE5 in the test tube. One study using PDE5 from human platelets measured an IC50 (the concentration that halves enzyme activity) of 0.432 µmol/L [6]; another, using human recombinant PDE5, measured 5.9 µM for icariin against 74 nM for sildenafil, roughly 80 times weaker [7].

In rats with damaged erectile nerves, 4 weeks of daily oral icariin was tested at 1, 5 or 10 mg/kg; the low-dose group had significantly higher erectile pressure than untreated rats, and a single dose 2 hours before testing did not help [8]. The same study found more nerve-related markers in penile tissue and longer nerve outgrowth in cultured nerve cells, so icariin may also act on nerves [8]. Reviews of icariin list further pathways in animals, including nitric oxide signalling and testosterone production [9][2].

Lab potency does not tell you what happens after you swallow a capsule. About 91.2% of oral icariin is converted to icariside II by gut bacteria [9], and when 30 healthy men took a single dose of 370 to 1,110 mg of a standardised Epimedium extract, icariin itself was below detection limits in their blood; icariside II and desmethylicaritin were the main metabolites found [10].

No study has measured whether those blood levels are enough to block PDE5 in penile tissue. Rat doses don't translate directly to people, and rat erectile pressure is not the same outcome as a man's erection during sex. Until a trial in men measures erections, the mechanism is a reason to study horny goat weed, not evidence that it works.

Because no trial has tested horny goat weed alone for ED, there is no dose with evidence behind it. LiverTox notes that products come as 250 or 500 mg tablets and capsules, usually taken once a day, and are often combined with other botanicals [4]. The two blend trials don't help here: their abstracts don't give how much Epimedium each product contained [3][5].

The best human safety data on dose come from a single-dose study: 370, 740 or 1,110 mg of a standardised Epimedium extract was well tolerated, with no adverse effects observed, in 30 healthy men [10]. That covers one dose in healthy volunteers, not weeks of use, and says nothing about erections.

In a randomised, double-blind crossover trial, 63 Thai men with mild or mild-to-moderate ED took Cappra, a traditional herbal product, or placebo for 2 weeks each, with a 1-week washout between. LiverTox lists the product as having five ingredients, including Epimedium [4]. Sixty-one men finished, and the erectile function score rose by 4.87 points on the blend against 3.44 on placebo (p = 0.032) [3]. That is a difference of about 1.4 points, after only 2 weeks per treatment, with no way to tell which herb was responsible.

In an open-label trial, 49 men (mean age 62.7) with symptoms of ageing were randomised to a six-ingredient preparation of aged garlic extract, ginseng, oriental bezoar, velvet antler, cuscuta seed and epimedium herb, or to Kampo medicine, mainly kamishoyosan, for 6 months. IIEF-5 scores increased in the preparation group (p = 0.02 for the group-by-time interaction) [5]. There was no placebo, men knew what they were taking, and the blend included ginseng, which has its own ED trials.

Horny goat weed is one of the most common ingredients in men's sexual health supplements. A review of the six top-rated ED supplements on Amazon found ginseng, horny goat weed, L-arginine and tongkat ali the most popular ingredients, and concluded that human studies of these ingredients are limited and have yielded no definitive findings on ED [11]. A systematic review of 32 best-selling testosterone and ED supplements found horny goat weed among the most common ingredients and no published randomised trial for any whole product [12].

A urologist's guide to the top-selling men's sexual health supplements listed horny goat weed among the most common ingredients and called the literature on these substances generally of low quality [13]. Even a 2025 review that describes Epimedium's compounds as improving sexual function and regulating hormones presents it as groundwork for further studies and clinical guidance [14].

There is no randomised trial of horny goat weed or icariin alone in men with ED, no dose-finding study, no comparison with an approved ED medicine and no long-term safety study. A rat study found that icariin added to daily sildenafil preserved erectile pressure better than either alone after nerve injury [15], but that combination has not been tested in men.

The American Urological Association guideline asks clinicians to inform every man with ED of all treatments that aren't contraindicated as potential first-line options, through shared decision-making [16], and the 2025 European Association of Urology guidelines say patients should be fully counselled about all available treatment modalities [17]. ED is linked to heart disease, high blood pressure and diabetes [18], so a medical check comes first, including a test for low testosterone where symptoms suggest it.

Among supplements, Korean ginseng and L-arginine carry a "likely" verdict for ED on this site, based on human trials. If your concern is desire rather than erections, see horny goat weed for low libido.

LiverTox describes horny goat weed as generally well tolerated, with possible abdominal discomfort and nausea and rare hypersensitivity reactions, skin rash and allergic dermatitis. It rates it an unlikely cause of clinically apparent liver injury: no liver problems were reported in small trials, though rare liver injuries have been reported with multi-ingredient products containing Epimedium [4].

Memorial Sloan Kettering lists sweating or feeling hot, a rapid irregular heartbeat, increased energy and mood changes as side effects, and says not to take Epimedium if you have heart disease [19]. That advice rests on a published case of tachyarrhythmia and hypomania [20]: a 66-year-old man with congestive heart failure who had taken Epimedium daily for 2 weeks was hospitalised with chest pain, shortness of breath and a new arrhythmia [19]. Another case report described a vasculitic rash in a man taking ginkgo and/or horny goat weed [21]. In the five-herb blend trial, dizziness (13.3% vs 9.6% on placebo), face numbness and tachycardia (1.6% each) were reported [3].

Memorial Sloan Kettering also advises caution with hormone-sensitive cancers, because Epimedium compounds showed estrogenic effects in lab studies [19].

Memorial Sloan Kettering advises not taking Epimedium with drugs processed by the liver enzyme CYP3A4 or with aromatase inhibitors; both interactions come from lab findings, and their clinical relevance is not known [19]. The ED-specific question is combining horny goat weed with a PDE5 inhibitor, which has only been studied in rats [15].