What is horny goat weed? Does it work?

Horny goat weed is perhaps the most literally named supplement of all time. Centuries ago, when Chinese farmers noticed that goats seen eating the herb later seemed to be unusually “in the mood,” this herbal extract became a mainstay treatment for erectile dysfunction (ED) in Traditional Chinese Medicine. It’s long since made its way into the ever-growing ED supplements industry, too. 

Does horny goat weed really work for ED? Is this herb the magical answer to all your libido and sexual performance woes? Let’s see what the research has to say.

Horny goat weed is an extract from the epimedium grandiflorum plant, a flowering shrub native to Asia, Africa, and parts of Europe. Also called by its Chinese name, yin yang huo, horny goat weed has been used for hundreds of years as a Chinese medicinal herb for treating ED and low libido. 

While this herb’s popularity in the East may have started with some snacking goats, it’s made a splash in the Western supplements industry over the past hundred years or so. Touted as an aphrodisiac and erection booster, horny goat weed is available in tablet, capsule, tea, or powder form—either on its own or as part of other supplement formulations. (It might be listed on a label as Epimedium, Epimedium sagittatum, Epimedium grandiflorum, or Epimedium koreanum). 

The active ingredient in horny goat weed is icariin, a compound that’s been studied in animals for a wide range of potential benefits. These include potential anti-inflammatory benefits which could have a positive impact on  diseases like cancer, asthma, lupus, and more—though it hasn’t been established in formalized clinical trials if humans actually experience these potential effects. 

Icariin also inhibits PDE5 (phosphodiesterase type 5), which is how drugs like Viagra or Cialis work. It’s possible horny goat weed could have similar effects as PDE-5 inhibitors, but one large review study showed the jury’s still out on how effective it is at improving erections.  

Let’s take a closer look at how effective horny goat weed really is. 

When it comes to improving erectile function, numerous studies show that horny goat weed’s active ingredient, icariin, might work—at least in rats. These rodent studies have shown icariin to repair damaged blood vessels impairing erectile function, improve blood flow to the penis, and increase testosterone levels, among other positive benefits. 

Some other studies indicate epimedium (the plant from which horny goat weed is extracted) may slow down aging in rats, which is one potential contributing factor in erectile dysfunction. 

How does that translate into humans? Unfortunately, we don’t know. There haven’t been any  sizeable studies on how horny goat weed or icariin may impact ED in humans.  Studies in the laboratory suggest that this plant extract is probably about 10-fold less potent than sildenafil (Viagra) in its action.  Since absorption of the herb may be variable (affected by food, especially fat, it’s not clear whether it would work to treat erection problems. Clinical studies on humans would be needed to say for sure how this herb could impact erectile function in humans. 

If horny goat weed works for ED—and that’s a big “if” in humans—here’s how. 

Its active ingredient icariin is a PDE5-inhibitor, similar to Viagra or Cialis (though significantly  less potent than these prescription drugs) and may also increase testosterone production, which can be important when it comes to libido. Some studies show it could affect repair of damaged blood vessels and nerves that may be involved with erectile dysfunction. 

How fast does horny goat weed work? We certainly don’t know the answer to that in humans, but most studies on rats have been over the course of weeks or months. We don’t have evidence that this herb works within minutes to hours like its prescription counterparts. 

So, what’s the verdict on Viagra vs. horny goat weed? We can’t say for sure, but the limited rodent studies we have seem to tell us Viagra is probably far more potent. 

Without peer-reviewed human studies where this herb is given to men and compared to other drugs or placebo (sugar pills), we just can’t know with certainty. One thing we know for sure is that Viagra is tested and regulated, while an herbal supplement like horny goat weed is not. It comes in many varieties, manufactured by many different companies, so there is likely a lot of variation in the concentration and effectiveness of different preparations, and there’s little to no regulation or safety data on over-the-counter supplements like these. 

Horny goat weed might offer more benefits beyond erectile function and libido. Again, while we don’t have human studies, there’s been some evidence that horny goat weed acts in ways that could theoretically offer benefits for following medical conditions such as:

• Osteoporosis

• Chronic obstructive pulmonary disease (COPD)

• Heart disease

• Neurodegenerative diseases

• Lipid disorders

• Chronic inflammation

Just like using horny goat weed for ED, none of these other potential benefits have been studied in humans. Rats seem to be getting a good number of health benefits from this herbal remedy, but we just don’t know that humans would fare the same.    

According to some published studies, horny goat weed is probably safe when taken by mouth in appropriate doses in the short term.  However, this herb can interfere with or change the action of a wide variety of medications, including drugs for high blood pressure and to thin the blood.

Side effects of horny goat weed may include upset stomach, dry mouth, nosebleeds, dizziness, and rapid heartbeat. Horny goat weed can also have adverse effects when taken with other medications, supplements, or health conditions.

Don’t take horny goat weed if you have a bleeding problem or are scheduled to have surgery; it may affect your blood’s clotting ability. Horny goat weed can also change hormone levels, so you shouldn’t take it if you have a hormone-sensitive cancer.

It may be unadvisable to take horny goat weed if you’re on certain medications or supplements, including: 

• Medications containing estrogen

• People who are taking medications to lower estrogens or block female hormones

• Drugs or supplements that lower blood pressure

• Blood thinners or other drugs or supplements that slow blood clotting

• Drugs or supplements processed by the liver (many medications are processed by the liver)

Let your healthcare provider know about any dietary supplements and medications you’re taking.

If you struggle to get or maintain erections, there are options with a lot more research behind them than horny goat weed. The first-line treatment is a class of drugs called PDE-5 inhibitors, which include: 

• Viagra (sildenafil)

• Cialis (tadalafil)

• Levitra (vardenafil)

• Stendra (avanafil)

• Compounded medications such as Ro Sparks

These drugs all come in different doses, and take effect at different rates, and each person will respond better to some than others. Speak with your healthcare provider about which is the best option for you.

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How we reviewed this article

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.

Editorial Guidelines | Medical Review Process

Current version

September 17, 2024

Written by

Michael Martin

Fact checked by

Raagini Yedidi, MD and Peter Schlegel, MD

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About the medical reviewers

Raagini Yedidi, MD

Raagini Yedidi, MD, is an internal medicine resident and medical reviewer for Ro.

Peter Schlegel, MD

Peter Schlegel, MD, is a Ro Advisor, board-certified urologist, and internationally acclaimed expert in the treatment of male fertility. For nearly 20 years, Dr. Schlegel served as the chair of Urology at New York Presbyterian/Weill Cornell. He now focuses on providing the best patient care possible for urologic conditions through his private practice.