Horny Goat Weed (Epimedium)
Summary
Horny goat weed is sold for sexual function, but no published placebo-controlled human trial of Epimedium alone was found for erections or libido. The best human data are bone studies in postmenopausal women (grade C). Icariin's PDE5 effect comes from lab tests, case reports describe serious reactions, and some products have contained hidden sildenafil.
Key facts
- None found for Epimedium alone in people; erection data come from enzyme tests and a rat study[4][5]
- A 24-month trial in 100 postmenopausal women: icariin 60 mg/day plus soy isoflavones kept spine and hip bone density stable while placebo lost bone[1]
- After an Epimedium prenylflavonoid extract, icariin itself was below detection; desmethylicaritin was the main metabolite[2]
- FDA has posted a recall of a 'horny goat weed' capsule found to contain undeclared sildenafil and a sildenafil analogue[9]
- 3 graded human outcomes on this page
- October 13, 2026
How it works
ProposedIn lab tests icariin inhibits PDE5, the enzyme blocked by sildenafil, but about 80 times more weakly than its chemically modified derivative, which matched sildenafil. In nerve-injured rats, oral icariin improved erectile pressure responses. Neither effect has been confirmed with Epimedium in people.[4][5]
What the human research says
Human trials only, one row per outcome. The form column shows what each trial actually tested. Grades follow our evidence-grading policy.
At a glance: strongest evidence per outcome
| Outcome | Grade | Effect | Strongest evidence | Rows |
|---|---|---|---|---|
| Bone | Grade C | Improved | RCT · n = 85 · 2007 | 2 rows |
| Fatigue | Grade D | No effect | Pilot RCT · n = 10 · 2021 | 1 row |
Every graded row
| Outcome | Effect | Grade | Best evidence | PMID |
|---|---|---|---|---|
| Spine and hip bone mineral density in late postmenopausal women | Improved | Grade C | RCT · n = 85 · 2007 Healthy late postmenopausal women with low bone density (T-score −2 to −2.5), Hong Kong Form: Epimedium-derived flavonoids: icariin 60 mg, daidzein 15 mg and genistein 3 mg daily · Dose: One daily dose of the flavonoid mix; all participants also received 300 mg calcium · Duration: 24 months Bone density stayed stable with the flavonoids while the placebo group lost 2.4% at the lumbar spine and 1.8% at the femoral neck; between-group differences were significant at 24 months. A bone-breakdown marker fell 39–43%. Estradiol and endometrial thickness did not change. | 17419678 (opens PubMed)Source [1] |
| Safety and a bone-formation marker (BSAP) with an Epimedium prenylflavonoid extract | Improved | Grade D | RCT · n = 58 · 2021 Healthy postmenopausal women aged about 58 (Singapore) Form: Purified Epimedium prenylflavonoid extract · Dose: 740 mg/day · Duration: 6 weeks No significant adverse symptoms and no changes in liver, blood or kidney tests. Prenylflavonoid intake was associated with higher bone-specific alkaline phosphatase (p<0.05) and a non-significant trend toward lower TRAF6, an osteoclast marker. | 34352588 (opens PubMed)Source [2] |
| Symptom severity, pain and fatigue in Gulf War illness | No effect | Grade D | Pilot RCT · n = 10 · 2021 Men with Gulf War illness (USA) Form: Epimedium sagittatum extract standardized to 20% icariin · Dose: 500 mg/day then 1,000 mg/day (100 and 200 mg icariin) · Duration: 30 days per dose level after 30 days of placebo Neither the lower nor the higher dose reduced symptom severity compared with placebo. | 33915962 (opens PubMed)Source [3] |
Forms
| Form | Elemental % | Absorption (human data) | GI tolerance | Studied for |
|---|---|---|---|---|
| Extract standardized to icariin (10–20%) | Varies[10][3] | Icariin was not detectable in blood after an Epimedium flavonoid extract; it is converted to metabolites such as desmethylicaritin and icaritin.[2] | The Gulf War illness study abstract reports no Epimedium-specific adverse effects; case reports describe muscle injury and psychosis with over-the-counter products.[3][6][7] | Gulf War illness symptoms (500–1,000 mg/day of a 20% icariin extract) |
| Purified Epimedium prenylflavonoid extract | Varies[2] | Desmethylicaritin peaked at a median 60.9 nM; icariin and icariside I stayed below detection.[2] | No significant adverse symptoms and no liver, blood or kidney test changes over 6 weeks.[2] | Safety and bone markers in postmenopausal women (740 mg/day) |
| Icariin with soy isoflavones | Varies[1] | No head-to-head human absorption data.[1] | No change in estradiol or endometrial thickness over 24 months.[1] | Bone density in postmenopausal women (24 months) |
Studied doses
Doses studied in human trials ranged from 60 mg/day of icariin (with soy isoflavones) for 24 months, to 740 mg/day of a prenylflavonoid extract for 6 weeks, and 500–1,000 mg/day of a 20% icariin extract (100–200 mg icariin) for 30 days at each level. No trial has tested Epimedium alone for sexual function.[1][2][3]
Interactions
Published interactions only: each row cites a source. No row means none was found in our sources, not that a combination is safe.
Medicines
- Nitrates (with adulterated products)FDA safety communicationFDA posted a recall of a 'horny goat weed' capsule containing undeclared sildenafil, warning that it may interact with nitrates and cause a life-threatening drop in blood pressure. This applies to tainted products, not to Epimedium itself.[9]
- Buprenorphine and other CYP3A4-metabolized drugsCase reportOne case report describes worse opioid cravings after starting Herba Epimedii during buprenorphine treatment; the authors propose a CYP3A4 interaction based on lab data.[8]
- Dopaminergic Parkinson's medicinesCase reportOne case report describes new psychosis in a person with Parkinson's disease after a month of daily horny goat weed; the authors suggest CYP1A2 inhibition may have raised ropinirole levels, but the product's contents were unknown.[6]
Who should be careful
- People who use nitrate heart medicines
- Some products sold as horny goat weed have contained hidden sildenafil, which the recall notice posted by FDA warns can drop blood pressure dangerously with nitrates.[9]
- Parkinson's disease or other dopaminergic therapy
- A case report links daily horny goat weed to new psychosis in a person taking ropinirole and levodopa.[6]
- People taking buprenorphine
- A case report describes increased opioid cravings after starting Herba Epimedii.[8]
- Pregnancy and breastfeeding
- The cited trials enrolled postmenopausal women or adult men, so they give no safety data for these groups; product labels advise consulting a professional first.[1][2][3][10]
- Unexplained muscle pain or cramps
- A 33-year-old man developed severe muscle spasms with creatine kinase up to 3,271 U/L and raised creatinine after a month of an online Epimedium product; both improved in hospital after he stopped it.[7]
Talk to your pharmacist or clinician before starting a supplement, especially if you take prescription medicines.
How to read the label
- Label dose vs studied doseA typical label (500 mg extract at 10% icariin, one capsule twice daily) gives about 100 mg icariin a day. That matches the lower dose in the Gulf War illness study, which found no benefit, and exceeds the 60 mg/day used in the bone trial.[10][3][1]
- Check the icariin percentageExtracts in studies and on labels range from 10% to 20% icariin, so the same extract weight can give twice the icariin.[10][3]
- Beware of multi-ingredient 'male enhancement' productsFDA has posted a recall of a horny goat weed capsule that contained undeclared sildenafil and a sildenafil analogue.[9]
Cost per studied dose, without the sales pitch
Compare any product you already have by the amount it delivers, not by capsule count or front-of-pack weight.
Cost per studied dose
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Frequently asked questions
Does horny goat weed work for erections?
There is no published placebo-controlled human trial of Epimedium alone for erections. Its icariin inhibits PDE5 in lab tests and helped nerve-injured rats, but that has not been confirmed in people.[4][5]
Is icariin like Viagra?
Both act on PDE5 in the lab, but icariin was about 80 times weaker than sildenafil, and icariin itself was not detected in blood after an oral Epimedium extract.[4][2]
Does horny goat weed raise testosterone?
No human trial of Epimedium alone measuring testosterone was found. The rat study measured testosterone, but rat data do not show an effect in people.[5]
Is horny goat weed safe?
A 6-week trial in 58 women found no adverse symptoms or lab changes, but case reports describe severe muscle injury and psychosis, and a horny goat weed product was recalled (notice posted by FDA) after it was found to contain sildenafil.[2][7][6][9]
Does it help bones?
In a 24-month trial, postmenopausal women given icariin 60 mg/day with soy isoflavones kept their bone density while the placebo group lost bone. Icariin's own role cannot be separated.[1]
How much icariin is in a typical capsule?
Labels list 500 mg of extract at 10% icariin (50 mg) per capsule, twice daily, which is about 100 mg icariin a day.[10]
Sources
- [1]Epimedium-derived phytoestrogen flavonoids exert beneficial effect on preventing bone loss in late postmenopausal women: a 24-month randomized, double-blind and placebo-controlled trial.. J Bone Miner Res, 2007. RCT
- [2]Randomized, double-blind, placebo-controlled trial to examine the safety, pharmacokinetics and effects of Epimedium prenylflavonoids, on bone specific alkaline phosphatase and the osteoclast adaptor protein TRAF6 in post-menopausal women.. Phytomedicine, 2021. RCT
- [3]A Placebo-Controlled, Pseudo-Randomized, Crossover Trial of Botanical Agents for Gulf War Illness: Reishi Mushroom (Ganoderma lucidum), Stinging Nettle (Urtica dioica), and Epimedium (Epimedium sagittatum).. Int J Environ Res Public Health, 2021. pilot-RCT
- [4]Potent inhibition of human phosphodiesterase-5 by icariin derivatives.. J Nat Prod, 2008. animal-study
- [5]Erectogenic and neurotrophic effects of icariin, a purified extract of horny goat weed (Epimedium spp.) in vitro and in vivo.. J Sex Med, 2010. animal-study
- [6]New-Onset Psychosis in a Person with Parkinson's Disease after "Horny Goat Weed" Use.. Mov Disord Clin Pract, 2026. observational
- [7]Herba Epimedium (Horny Goat Weed) Toxicity With Severe Muscle Spasms and Elevated Creatine Kinase and Creatinine: A Case Report.. Cureus, 2025. observational
- [8]Herba Epimedii and Increased Opioid Cravings While on Buprenorphine: A Case Report.. Cureus, 2024. observational
- [9]EnShiShiXiangNiShangMaoYouXianGongSi Issues Voluntary Nationwide Recall of ENDURANCE BOOST WITH HORNY GOAT WEED Capsules Due To Presence of Undeclared Propoxyphenylsildenafil and Sildenafil. U.S. Food and Drug Administration, 2025. safety-communication
- [10]Standardized Horny Goat Weed (Nature's Way), DSLD label 79133: 500 mg Epimedium extract standardized to 10% icariin (50 mg) per capsule. NIH Office of Dietary Supplements, Dietary Supplement Label Database, 2017. label
What changed
- Independent review: the 2025 Endurance Boost recall was a voluntary company recall posted by FDA, not an FDA recall; wording corrected. All PMIDs re-checked.
- Adversarial review pass: every evidence row, key fact, form, label line, FAQ and insight re-read against its PubMed abstract, PMC full text, fact sheet, FDA page or DSLD label; all PMIDs re-checked by esummary (titles and years match; no retraction or expression-of-concern flags). Fixed: BSAP result restated as an association (as in the abstract), Gulf War illness tolerability wording narrowed, muscle-injury outcome restated as improvement in hospital. Page set indexable.
- First draft. Every PMID checked against NCBI E-utilities esummary (title and year from the record) and abstracts read for each cited row; Gulf War illness doses and completer count from the PMC full text (PMC8037868); psychosis and muscle-injury case details from PMC full texts (PMC12911459, PMC12182873). FDA recall page and NIH DSLD label read directly. No NCCIH or NIH ODS fact sheet covers Epimedium. PubMed searches found no placebo-controlled human trial of Epimedium alone for sexual function.