Horny goat weed is the common name for plants in the Epimedium genus, and its main active compound is icariin. The human studies are mostly about bone: two systematic reviews of Epimedium in primary osteoporosis report bone density results that partly disagree, and short trials in postmenopausal women found it well tolerated. No human study covered here tested sexual function, and none measured testosterone.
The name is discussed in a 2020 review of ED supplement ingredients, which says the herb is “named after its aphrodisiac effects on goats who ate the leaves of E. grandiflorum.” A popular goat-herder story is also told, and one consumer guide says it found no credible source for that story.
Quick facts at a glance
| Topic | What the research shows |
|---|---|
| What it is | Common name for Epimedium plants. The main active compound is icariin, a flavonoid. The Memorial Sloan Kettering guide lists Epimedium sagittatum, E. grandiflorum and E. brevicornum as scientific names. |
| Forms | Raw herb, tablet or capsule, according to the UTEP facts sheet. The human trials used a purified or standardized prenylflavonoid extract. |
| Doses used in studies | 740 mg daily (2021 trial); single doses of 370, 740 or 1,110 mg (2019 study); 1, 5 or 10 mg/kg icariin (rat study). See the dose section below. |
| Typical study length | Six weeks (2021 trial); one dose with 48 hours of blood sampling (2019 study); four weeks (rat study). |
| Main studied uses | Bone density and bone markers; erectile function in rats only. No human sexual function trial is covered here. |
What does the human research show?
The results below run from the strongest human evidence to the weakest. The bone density reviews come first, then the two short human trials, then the sexual function and testosterone questions, which have no human data here.
Does it help bone density?
The strongest human data come from two systematic reviews. A systematic review combines results from several studies, and the ingredient evidence vs marketing claims guide explains how to weigh one.
The 2025 meta-analysis of Epimedium for osteoporosis pooled 10 randomized controlled trials with 890 people who had primary osteoporosis. It compared Epimedium as an add-on or alternative with traditional osteoporosis drug treatments. Epimedium groups did better on the overall efficacy rate (odds ratio 3.80). They also showed bone mineral density gains at the lumbar spine, femoral neck and distal radius, and faster relief of lower back pain. Adverse reactions were low, mainly mild gastrointestinal reactions or skin allergies. The authors say more high-quality studies are needed to verify long-term efficacy.
The review frames Epimedium as a possible adjunct or alternative. That is a research comparison, not advice to swap a prescribed medicine. Any change to an osteoporosis medicine belongs with your prescriber.
The 2024 review of Epimedium total flavonoids pooled 6 trials with 838 participants. Lumbar spine bone density differed statistically from control, with a mean difference of 0.03. The authors say its clinical significance needs consideration because the 95% CI nearly crosses the line of clinical invalidity. Femoral neck density showed no difference, and complication rates were comparable between groups. The control groups included other Chinese patent medicines and calcium and vitamin D supplements. The authors rate the quality of the evidence as moderate and low under GRADE, a system for rating how certain a body of research is.
The two reviews disagree on the femoral neck. The 2025 review reports a significant gain there, and the 2024 review reports none.
What do the two short human trials show?
In 2021, Yong and colleagues randomized 58 postmenopausal women, average age 57.9, to 740 mg of an Epimedium prenylflavonoid extract daily or to placebo for six weeks. The 2021 placebo-controlled trial in postmenopausal women was double-blind, and its main outcomes were safety and how the extract was absorbed. It found no significant adverse symptoms and no changes in liver, blood or kidney tests. The main metabolite in blood was desmethylicaritin. Bone-specific alkaline phosphatase, a bone marker, was higher in the Epimedium group (p < 0.05). A trend in a second marker, TRAF6, did not reach statistical significance (p = 0.068).
In 2019, Teo and colleagues gave single doses of 370, 740 or 1,110 mg to 30 healthy men in a placebo-controlled trial, and sampled blood for 48 hours. The 2019 single-dose study in healthy men found the extract well tolerated, with no adverse effects observed. Desmethylicaritin levels rose with higher doses. Icariin and icaritin were below detection limits.
Does it help erectile dysfunction or sex drive?
No human trial covered here tested sexual function. The support for erectile function comes from rat studies. In one rat study described in the 2020 review, icariin at 1, 5 or 10 mg/kg over four weeks increased pressure in the penis after nerve injury. The 1 and 10 mg/kg groups showed significant increases, and the 5 mg/kg group did not reach significance. The review notes that icariin has PDE5 inhibitor activity in lab tests, and that further work in animal and human models is scarce.
The same review calls PDE5 inhibitors such as sildenafil a mainstay of ED treatment. None of the studies covered here compares horny goat weed with a prescription drug for erectile dysfunction.
Which herb is best for erectile dysfunction?
The 2020 review found limited data for most ingredients, including horny goat weed. It says L-arginine is “the only ingredient in ED-oriented nutraceuticals to reproducibly demonstrate significant improvements in erectile function across multiple human trials.” Horny goat weed is not on that list. Zinc, another common ingredient in these products, has its own page: zinc benefits evidence.
Does horny goat weed boost testosterone?
None of the human studies covered here measured testosterone. The Memorial Sloan Kettering guide says Epimedium “is thought to alter levels of certain hormones,” and the 2020 review says icariin “may mimic some properties of testosterone.” Those statements describe how it might work, not measured changes in people. Claims that it raises testosterone appear mainly in seller and consumer articles.
Does it have benefits for women?
The 2021 trial enrolled postmenopausal women. The 2024 and 2025 reviews pooled people with primary osteoporosis, so check each review’s full text for the sex and menopausal status of those participants. The trials measured bone density, bone markers and safety. The Memorial Sloan Kettering guide notes that Epimedium has estrogen-like effects and should be avoided in hormone-sensitive cancers.
What about its other traditional uses?
Memorial Sloan Kettering herb guide on Epimedium lists fatigue, arthritic and nerve pain, and sexual dysfunction among traditional uses. It says fatigue has not been studied in clinical trials. For Gulf War Illness, the guide reports that a 2021 crossover trial of Epimedium with two other botanicals did not find relief of symptoms.
How much was used in studies?
These are amounts researchers used in their studies. They are not a suggested amount for anyone.
| Study | Who took it | Amount used | Length |
|---|---|---|---|
| 2021 placebo-controlled trial | 58 postmenopausal women | 740 mg prenylflavonoid extract daily, or placebo | Six weeks |
| 2019 single-dose study | 30 healthy men | Single doses of 370, 740 or 1,110 mg | One dose, blood sampled for 48 hours |
| Rat icariin study (described in the 2020 review) | Rats with cavernous nerve injury | 1, 5 or 10 mg/kg icariin | Four weeks |
Each review pools trials that used different amounts. For the dose in each trial, the full text of each review is where to look. For timing and whether to take it with food, the product label and a pharmacist are the places to ask.
Is horny goat weed safe, and does it interact with medicines?
The Memorial Sloan Kettering herb guide and the UTEP horny goat weed facts sheet are the two main safety summaries. Safety results from the human trials are in the bone section above.
| Topic | What the sources say |
|---|---|
| Commonly reported effects | Sweating or feeling hot at high doses, rapid irregular heartbeat, increased energy and mood changes (Memorial Sloan Kettering guide). |
| Case reports | A 77-year-old man had a vasculitic rash, pain and burning after taking ginkgo and/or horny goat weed; symptoms stopped after the products were discontinued. A 66-year-old man with congestive heart failure had tachyarrhythmia and hypomania after two weeks of daily use (Memorial Sloan Kettering guide). |
| Heart disease | Listed as a reason not to take it, and a patient with heart disease had rapid irregular heartbeat and excitability (Memorial Sloan Kettering guide). |
| Hormone-sensitive cancers | The guide says Epimedium has estrogenic effects and should be avoided in patients with hormone-sensitive cancers (a clinical summary also says to use it with caution). |
| Drugs metabolized by CYP3A4 | Prolonged use can induce the CYP3A4 enzyme. Clinical relevance is not known (Memorial Sloan Kettering guide). |
| Aromatase inhibitors | Icariin may reduce the effect of anastrozole, exemestane and letrozole. Clinical relevance is not known. The guide lists these drugs under Do Not Take if. |
| Prescription erectile dysfunction drugs | The UTEP sheet says no known studies cover herb-drug interactions with these medicines, and it is not recommended to combine them without medical advice. |
| Pregnancy and breastfeeding | The UTEP sheet says safety has not been adequately studied in these groups. |
| Combination products | The UTEP sheet says yohimbé, which is sometimes combined with horny goat weed, may cause high blood pressure and behaviour changes at high doses. |
| Product quality | The UTEP sheet says quality control in some herbal supplements is lacking. |
Who should talk to a clinician first?
- Anyone with heart disease. The Memorial Sloan Kettering guide lists heart disease as a reason not to take it, citing a patient with heart disease who had rapid irregular heartbeat and excitability. The UTEP sheet advises consulting a qualified health provider before taking any product containing this herb.
- Anyone with a hormone-sensitive cancer. The Memorial Sloan Kettering guide says Epimedium may affect hormone levels and should be avoided in patients with hormone-sensitive cancers.
- Anyone taking drugs metabolized by CYP3A4, or an aromatase inhibitor such as anastrozole, exemestane or letrozole.
- Anyone taking a prescription medicine for erectile dysfunction.
- Anyone who is pregnant or breastfeeding.
- Anyone sensitive to Epimedium.
Erectile problems can have several causes, so a clinician is the right person to help sort out what applies to you. Bring the product label to that appointment.
What is still unknown?
- Sexual function and testosterone: none of the human studies covered here tested sexual function or measured testosterone.
- Size and length: the human trials are small, with 30 and 58 people, and ran for one dose or six weeks. The 2021 authors say the safety, mechanisms and therapeutic indications of Epimedium in humans are unknown.
- Bone results: the two reviews disagree on the femoral neck, and the 2024 lumbar result is small. The 2025 authors call for more high-quality studies on long-term efficacy. The Memorial Sloan Kettering guide says, “Scientific evidence to support use of Epimedium is limited.”
- Fracture outcomes: the reported outcomes are bone density, bone markers and back pain. For fracture data, check the outcomes table in the full text of each review.
- Mechanism: the PDE5 activity and estrogen-like effects were seen in lab and animal work. How they apply in people is not established.
- Interactions: the clinical relevance of the CYP3A4 and aromatase interactions is not known, and no known studies cover interactions with prescription erectile dysfunction drugs.
- Products: the trials used specific Epimedium extracts. A product labelled horny goat weed may use a different species or extract.
How do you read a horny goat weed label?
- Amount and form: look for the amount per serving in milligrams and whether the label lists the raw herb or an extract. Compare extracts with extracts, because the trials used a purified or standardized extract.
- Icariin: if the label states an icariin percentage or amount, that is the compound the research focuses on.
- Species: the label may name Epimedium sagittatum, E. grandiflorum, E. brevicornum or another species.
- Blends: according to the UTEP sheet, the herb is sometimes combined with yohimbé, saw palmetto, maca and other herbs. Memorial Sloan Kettering notes that when this herb is combined in a botanical “recipe,” it confounds the determination of any specific contributions from Epimedium. If a blend lists no amount for horny goat weed, you cannot tell what dose you are getting.
- Contamination and testing: the 2020 review says some ED supplements have been contaminated with PDE5 inhibitors. Ask the maker for its batch testing results before you buy.
- Reviews: the 2020 review notes that vendors may post fake reviews, so product ratings are not proof of effect.
For a broader guide to judging supplement claims against the research, read ingredient evidence vs marketing claims.
By ClinicalStudyConnect.com Research Desk
This article is for general information purposes only and does not constitute medical advice. Consult your doctor or qualified healthcare provider before making changes to your health routine.