What Does Horny Goat Weed Do? Epimedium, Icariin and the Evidence

What does horny goat weed do? Horny goat weed (epimedium) is a traditional Chinese herb used for vitality, libido and physical fatigue. Its main compounds, flavonoids called icariins, have been studied mostly in the lab and in animals. Human research is still limited, so the honest answer is: a long traditional record, promising early science, and no shortcuts. Here is what is known, what is not, and how to choose a product.

What is horny goat weed?

Horny goat weed is the common name for Epimedium, a group of leafy plants used in Chinese herbal practice for centuries. In traditional Chinese medicine it is called yin yang huo. The odd English name comes from a folk story about a goat herder who noticed his flock became more lively after grazing on the plant.

Supplements use the leaves and stems (the aerial parts), usually dried and concentrated into an extract. A 2011 review counts about 52 species. Memorial Sloan Kettering lists Epimedium sagittatum, Epimedium grandiflorum and Epimedium brevicornum; Primal Root+™ uses Epimedium sagittatum.

What does horny goat weed do in the body?

Memorial Sloan Kettering calls icariin "a major active constituent of Epimedium." It notes that, in laboratory studies, icariin promoted estrogen production and related compounds showed estrogen-like activity, and that the herb may affect hormone levels (see the safety notes below). A good label states how much icariin a serving provides.

Researchers have also looked at icariin and other epimedium flavonoids for antioxidant activity in cells and for effects on bone. Most of the research so far comes from cell and animal studies, and human trials are small. Memorial Sloan Kettering Cancer Center's herb database puts it plainly: the scientific evidence for epimedium is limited, and "More studies are needed to confirm its safety and efficacy."

The traditional uses

• Vitality and libido: Memorial Sloan Kettering notes it "is marketed as a dietary supplement for libido."
• Physical fatigue: Memorial Sloan Kettering notes it is "traditionally used for fatigue but it has not been studied in clinical trials."

Does horny goat weed work? What the research says

It helps to separate three levels of evidence:

1. Traditional use: long and consistent. That tells you what people have used it for, not how well it works.
2. Lab and animal studies: the bulk of the science. They explain possible mechanisms, especially for icariin, but results in animals do not always carry over to people.
3. Human studies: few and small, often using combination formulas, which makes it hard to credit any single herb.

So when you read that horny goat weed "boosts" anything, read it as marketing. A fair statement is that epimedium is a traditional herb for libido and vitality, with early research that is interesting but not settled.

What is horny goat weed combined with?

Memorial Sloan Kettering notes that published trials "tend to combine this herb in a botanical 'recipe,'" which makes it hard to tell what epimedium does on its own. Herbs and nutrients that can appear alongside it:

• Maca, an Andean root eaten as a food and used traditionally as an energizer.
• Asian ginseng, a traditional herb that has been studied for fatigue.
• L-arginine, an amino acid the body uses to make nitric oxide.
• Longjack (tongkat ali) and muira puama, traditional roots from Southeast Asia and the Amazon.

Our Primal Root+™ is also a combination formula. It is built on 1,000 mg of epimedium extract (horny goat weed, 100 mg icariins) per two-capsule serving, with maca, longjack, muira puama, Asian ginseng and L-arginine. It supports a healthy libido and improved blood flow.*

How to choose a horny goat weed supplement

Labels in this category vary a lot. Four things are worth checking before you buy:

1. Icariin stated on the label. For epimedium, an icariin figure next to the extract amount tells you what the extract was standardized to.
2. An epimedium amount per serving. Look for the milligrams of epimedium extract per serving next to its icariin figure, so you can compare products.
3. Third-party testing. Botanical extracts can vary from batch to batch. Look for a brand that tests each batch for purity and potency with an outside lab.
4. Sensible directions. The label should give a clear serving and a clear daily limit.

Every batch of Primal Root+ is third-party tested for purity and potency, and it is manufactured in USA with globally sourced materials in an NSF-certified, GMP-certified, FDA-registered facility. You can read how we test on the Our Standards page.

Is horny goat weed safe?

Some people should not use epimedium at all (see below), and it can interact with other medicines, so check with your healthcare provider before you start. Memorial Sloan Kettering notes that epimedium may affect hormone levels and lists these side effects: feeling hot or sweaty, a rapid, irregular heartbeat, an increase in energy, and mood changes. Points to keep in mind:

• Do not use it if you are pregnant or nursing, or under 18.
• Do not use it if you are sensitive to it; Memorial Sloan Kettering lists this as a reason not to take epimedium.
• Do not use it if you have heart disease; Memorial Sloan Kettering lists this as a reason not to take epimedium.
• Primal Root+ also contains L-arginine. Memorial Sloan Kettering warns that in people who have had a heart attack (an "acute myocardial infarction"), "arginine supplementation may increase risk of mortality," that "Long-term supplementation may worsen peripheral artery disease," and that limited studies suggest arginine supplementation "may increase breast tumor growth, but more research is needed." A past heart attack counts as heart disease, so the do-not-use line above applies; if you have peripheral artery disease or have or have had breast cancer, talk to your doctor before you start.
• Talk to your doctor first if you take any prescription medicine, including blood pressure medicines: Primal Root+ also contains L-arginine, and Memorial Sloan Kettering says arginine supplements can lower blood pressure, "so taking both at the same time may not be safe."
• Talk to your doctor first if you have diabetes or take blood sugar medicine (Primal Root+ also contains Asian ginseng, which NCCIH says might lower blood sugar), or if you have any known medical condition.
• Talk to your doctor first if you have an autoimmune condition or a bleeding disorder, or take a blood thinner: NCCIH says Asian ginseng, which Primal Root+ also contains, "may worsen autoimmune disorders and interfere with blood clotting."
• Do not use it if you have or have had a hormone-sensitive cancer; Memorial Sloan Kettering says epimedium should be avoided in that case.
• Do not use it if you take an aromatase inhibitor (such as anastrozole, exemestane or letrozole) or a medicine processed by the CYP3A4 enzyme (ask your pharmacist); Memorial Sloan Kettering lists these as reasons not to take epimedium, though it notes the clinical relevance is not known.
• Talk to your doctor first if you have another hormone-sensitive condition or take hormone therapy.
• Know the time limit for Asian ginseng, which Primal Root+ also contains: NCCIH says short-term use by mouth (up to 6 months) of Asian ginseng in recommended amounts appears to be safe for most people, but questions have been raised about its long-term safety.
• Stay within the serving on the label. More is not better with concentrated extracts.
• Stop and seek advice if you notice a racing heartbeat or feel unwell.

Frequently asked questions about horny goat weed

How long does horny goat weed take to work?

There is no reliable timeline from human research. Take it as the label directs, alongside good sleep, regular movement and a balanced diet, and do not exceed the recommended dose. Primal Root+ also contains Asian ginseng; NCCIH says short-term use by mouth (up to 6 months) of Asian ginseng in recommended amounts appears to be safe for most people, but questions have been raised about its long-term safety. NCCIH also says Asian ginseng "may worsen autoimmune disorders and interfere with blood clotting." Primal Root+ contains L-arginine too, and Memorial Sloan Kettering says arginine supplements can lower blood pressure, so taking them with blood pressure medicines "may not be safe," and that "Long-term supplementation may worsen peripheral artery disease." Do not use epimedium if you are pregnant or nursing or under 18, and check with your healthcare provider before you start if you have a known medical condition.

Is horny goat weed the same as icariin?

No. Horny goat weed is the plant, and icariin is one of the flavonoids in it. An extract can be standardized to a stated amount of icariins, which is the more useful number to compare.

Can I take horny goat weed every day?

Many supplements are designed for daily use at the serving on the label; do not exceed the recommended dose. Primal Root+ also contains Asian ginseng, and NCCIH says short-term use by mouth (up to 6 months) of Asian ginseng in recommended amounts appears to be safe for most people, but questions have been raised about its long-term safety. NCCIH also says Asian ginseng "may worsen autoimmune disorders and interfere with blood clotting." Primal Root+ contains L-arginine too, and Memorial Sloan Kettering says arginine supplements can lower blood pressure, so taking them with blood pressure medicines "may not be safe," and that "Long-term supplementation may worsen peripheral artery disease." Do not use epimedium if you are pregnant or nursing, are under 18, are sensitive to it, have heart disease or a hormone-sensitive cancer, or take an aromatase inhibitor or a medicine processed by the CYP3A4 enzyme; otherwise ask your healthcare provider whether daily use suits you.

Does horny goat weed have caffeine?

No. Epimedium itself contains no caffeine, but some combination products add stimulants, so read the full ingredient list.

Who is horny goat weed for?

Epimedium is a traditional herb for vitality and libido. It is not for anyone pregnant, nursing or under 18, anyone sensitive to it, anyone with heart disease or a hormone-sensitive cancer, or anyone taking an aromatase inhibitor or a medicine processed by the CYP3A4 enzyme; everyone else should check with a healthcare provider first.

Related reading from our Wellness Hub

• Maca: Meet Maca Root+™ for Energy, Mood & Libido
• Adaptogens 101: What Is an Adaptogen? Ashwagandha and Mushrooms
• Daytime Energy Without the Jitters: A Balanced Approach

Sources

• Memorial Sloan Kettering Cancer Center: About Herbs, Epimedium. Last updated April 5, 2023.
• NCCIH: Asian Ginseng. Last updated February 2025.
• Memorial Sloan Kettering Cancer Center: About Herbs, Arginine. Last updated February 10, 2022.
• Gonzales GF. Ethnobiology and Ethnopharmacology of Lepidium meyenii (Maca), a Plant from the Peruvian Highlands. Evidence-Based Complementary and Alternative Medicine, 2012
• Ma H, He X, Yang Y, et al. The genus Epimedium: an ethnopharmacological and phytochemical review. Journal of Ethnopharmacology, 2011

Individual results vary.

*These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease.