Icariin: does horny goat weed work like Viagra (sildenafil)?

Erectile dysfunction (ED) can be very distressing, leading people to look for all sorts of solutions. Of course, Viagra (and drugs like it) are the gold standard treatment for ED, but you might have heard of natural treatments like icariin (the active ingredient in horny goat weed). Does icariin work like Viagra does? Let’s dig in. 

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Icariin is a traditional Chinese medicinal herb that comes from the epimedium plant, a wildflower endemic to China. It's the active ingredient in horny goat weed (yin yang huo), a supplement many people take as an aphrodisiac or treatment for ED.

Icariin is available in tablets, capsules, teas, and powders.

Horny goat weed (icariin) and sildenafil citrate (brand name Viagra) work in similar ways: They inhibit phosphodiesterase 5 (PDE5), an enzyme that "turns off" an erection (Dell'Agli, 2008). 

Icariin is a much milder PDE5 inhibitor than Viagra and other prescription ED medications; it's about 80 times less potent than Viagra (Dell'Agli, 2008).

As an herbal supplement, icariin is available over-the-counter (sold as horny goat weed or as an ingredient in various supplement formulations). In contrast, Viagra requires a prescription and is available in different strengths.

So, we know icariin is less potent than Viagra but does this herb work? Several animal studies have found that icariin does inhibit PDE5, which allows the penis to fill with blood to form an erection. Another study found that horny goat weed seemed to benefit rats with blood vessel damage, allowing them to synthesize nitric oxide in penile tissue better than a placebo (Dell'Agli, 2008). 

But a word of caution here: There haven’t been any human trials on horny goat weed and ED. Icariin might work differently in the human body than on lab animals.

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If you're experiencing ED, it's a good idea to consult a healthcare provider and discuss your full medical history. In some cases, ED can signify a serious health condition, including heart disease, high blood pressure, or diabetes.

Once you’ve been fully evaluated, your healthcare provider can decide if it’s appropriate to prescribe an ED medication. These medications—including sildenafil citrate (brand name Viagra), tadalafil (brand name Cialis), and vardenafil (brand name Levitra)—are highly effective.

Before trying prescription medications, some people prefer to try natural supplements (like horny goat weed) to treat their ED. Some of the supplements on the market have more scientific backing than others. Learn more about natural ED supplements here.

Your erections will be best when you're healthy. Making simple lifestyle changes, such as getting regular exercise, eating a healthy diet, quitting smoking, and limiting your alcohol consumption, might be enough to improve ED in some cases.

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Every article on Health Guide goes through rigorous fact-checking by our team of medical reviewers. Our reviewers are trained medical professionals who ensure each article contains the most up-to-date information, and that medical details have been correctly interpreted by the writer.

Current version

January 18, 2022

Written by

Michael Martin

Fact checked by

Steve Silvestro, MD

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About the medical reviewer

Steve Silvestro, MD, Ro

Dr. Steve Silvestro is a board-certified pediatrician and Associate Director, Clinical Content & Education at Ro.