Flavonol Glycosides
Icariin (Icaritin)Principal active compound; PDE5-inhibiting flavonol glycoside
Major
Epimedins A, B & CRelated flavonoid compounds[2]
Present
Sexual Health · Same Mechanism as Prescription PDE5 Inhibitors
Biological Overview
Epimedium is a species with numerous cultivars (Nanum, Rose Queen, White Queen) and hybrids, also widely grown for ornamental purposes in gardens — including hybrids such as E. x rubrum and E. x versicolor.
Life CyclePerennial herb
UseMedicinal & ornamental
Shared Drug ClassPDE5 Inhibitor
Marker CompoundIcariin
Botanical Classification
Taxonomy & Identification
- Latin Name
- Epimedium grandiflorum C. Morren
- Family
- Berberidaceae
- Common Names
- Horny Goat Weed, Épimède
- Chinese Names
- Yin Yang Huo, Herba Epimedii
- Parts Used
- Leaves
From Chinese Folklore to a Verified Mechanism
History & Tradition
Epimedium has been traditionally used in Chinese medicine specifically to treat impotence — its Chinese name, Yin Yang Huo, directly reflects this use, and traces to a folk account of a goat herder noticing increased sexual activity in goats that had grazed on the plant.
What makes this plant's research history genuinely notable is how directly modern pharmacology confirmed the traditional use: icariin, its principal compound, was found to inhibit the exact same enzyme — PDE5 — targeted decades later by sildenafil and the prescription erectile dysfunction drugs that followed it.
⚠ Critical Safety Information
This Herb Shares a Mechanism With Viagra — and That Mechanism's Most Dangerous Interaction
Because icariin inhibits PDE5 the same way prescription erectile dysfunction drugs do, and those drugs are absolutely contraindicated with nitrate medications due to risk of severe, potentially fatal hypotension, the same logic and pharmacology applies here. See Safety & Drug Interactions before considering use.
The Key Molecule
Icariin — Deep Dive
A single flavonol glycoside responsible for nearly every documented effect of this plant — and its central safety consideration.
🎯
Confirmed PDE5 Inhibitor
Icariin and its derivatives potently inhibit human phosphodiesterase-5 (PDE5) across all three of its isoforms, which can directly support the plant's traditional use.[3]
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Bone-Building Activity
Icariin from Epimedium pubescens increases the proliferation and differentiation of human osteoblasts, the cells responsible for building new bone.[6]
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Neuroprotective Activity
Active components of Epimedium, alongside those of Astragalus membranaceus and Radix Puerariae, reduce cognitive deficits and exert neuroprotective effects in Alzheimer's disease research models, including reducing brain iron overload and inhibiting beta-amyloid plaque accumulation.[4]
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Standardization Marker
Icariin content is the standard marker compound used to standardize Epimedium extracts, with its pKa and concentration determinable by capillary electrophoresis.[1]
⚠ Critical Safety Information
Icariin's Mechanism Is Pharmacologically Identical to a Drug Class With an Absolute Contraindication
PDE5 inhibition is precisely the mechanism by which prescription drugs like sildenafil work — and it is precisely why those drugs cannot be combined with nitrate medications, since the combined effect can cause severe, potentially fatal blood pressure drops. Because icariin works through the same enzyme target, this is not a remote theoretical concern. See Safety & Drug Interactions below for full detail.
Available Forms
Parts Used & Available Forms
Only the leaves are used, traditionally prepared as a decoction.
The traditional galenic form documented for this plant is a decoction of the leaves. Commercial supplements are most commonly sold as standardized extract capsules, with potency typically expressed as a percentage of icariin content.
Clinical Dosimetry
Dosages
Documented across two separate human trials, each targeting a different outcome.
The 2019 pharmacokinetic trial found single doses up to 1,110 mg well tolerated with no adverse effects in healthy male subjects. This does not establish a recommended ongoing daily dose — confirm dosing with a healthcare provider, and review Safety & Drug Interactions before any use.
Phytochemistry
Composition
A simple, well-characterized flavonoid profile centered on icariin.
Metabolites
Icariside I & IIPrenylflavonoid metabolites detected after oral ingestion
Present
DesmethylicaritinPrenylflavonoid metabolite
Present
🎯
PDE5 Inhibition
Icariin and its derivatives inhibit human phosphodiesterase-5 across all three isoforms, which can support the plant's traditional use.[3]
🧠
Neuroprotective & Anti-Alzheimer's
Active components reduce cognitive deficits, exert neuroprotective effects by reducing brain iron overload, and inhibit beta-amyloid plaque accumulation in Alzheimer's disease models.[4]
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Bone Loss Prevention
Epimedium brevicornum prevents bone loss in menopausal women.[5]
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Osteoblast Stimulation
Icariin from Epimedium pubescens increases proliferation and differentiation of human osteoblasts.[6]
🛡️
Related Species
Neuroprotective
Epimedium sagittatum is neuroprotective, a property documented separately from the broader Alzheimer's research above.[7]
Clinical Applications
Clinical Indications
Three documented indications, anchored by genuine clinical trial support for bone health specifically.
❤️
Sexual Function
Traditional, Mechanism-Supported
- Impotence and sexual asthenia, the central traditional indication.
Pharmacodynamics
Mode of Action
No distinct mechanism section is detailed in the primary phytotherapy literature for this plant; the mechanism below is drawn from its documented PDE5-inhibition property, the central pharmacological finding for this herb.
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PDE5 Enzyme Inhibition
Icariin and its derivatives inhibit phosphodiesterase type 5 (PDE5), the enzyme responsible for breaking down cyclic guanosine monophosphate (cGMP). Since cGMP is the downstream signal that causes smooth muscle relaxation and vasodilation, inhibiting its breakdown sustains and amplifies that vasodilatory effect — the same mechanism by which prescription PDE5 inhibitor medications work.[3]
Clinical Safety
Safety & Drug Interactions
A standardized extract was well tolerated in human trials — but one interaction risk is genuinely serious.
🚫 Absolute Contraindication: Nitrate Medications
Do Not Combine With Nitroglycerin or Any Nitrate Medication
The primary phytotherapy literature for this plant does not include a documented adverse-effects or interactions section. However, icariin's confirmed PDE5-inhibiting mechanism is pharmacologically identical to that of prescription drugs like sildenafil (Viagra), tadalafil (Cialis), and vardenafil (Levitra). Those drugs carry an absolute, well-established contraindication against use with nitrate medications — including nitroglycerin (sublingual tablets, sprays, and patches), isosorbide mononitrate, and isosorbide dinitrate — because the combination can cause severe, unpredictable, and potentially fatal hypotension. Because icariin acts through the same enzyme target, the same risk logically and pharmacologically extends to Horny Goat Weed. Anyone taking any form of nitrate medication for angina or heart conditions should not take this herb.[3]
What Has Been Studied
- Standardized extract well tolerated: a human trial testing single doses up to 1,110 mg reported no adverse effects over 48 hours of monitoring.[10]
- Idiosyncratic hepatotoxicity concern: a related compound, icariside II, has been linked to NLRP3 inflammasome-mediated liver toxicity in laboratory research, an area warranting continued attention.
Other Precautions
- Other PDE5-affecting medications: combining with prescription erectile dysfunction drugs is a reasonable theoretical concern for additive effects, given the shared mechanism.
- Blood pressure medications: given the vasodilatory mechanism, discuss use with a healthcare provider if you take any blood-pressure-lowering medication.
- Pregnancy and breastfeeding: avoid due to insufficient safety data.
Clinical Disclaimer: This monograph is for educational and professional reference only. It does not constitute medical advice, diagnosis, or treatment guidance. The nitrate interaction described above should be treated as an absolute contraindication. Always consult a qualified healthcare provider before starting Horny Goat Weed, particularly if you have any cardiovascular condition, take any heart or blood pressure medication, or take any other PDE5-affecting medication or supplement.
Common Questions
Frequently Asked Questions
How does Horny Goat Weed actually work?
Its principal compound, icariin, and its derivatives inhibit human phosphodiesterase type 5 (PDE5) — the same enzyme target as the prescription medications sildenafil (Viagra), tadalafil (Cialis), and vardenafil (Levitra). This mechanism, demonstrated in laboratory research, is consistent with the plant's traditional use for impotence.
Is it dangerous to combine Horny Goat Weed with nitrate medication?
Yes, and this should be treated as a serious, absolute contraindication, not a minor caution. Because icariin works through the same PDE5-inhibiting mechanism as prescription erectile dysfunction drugs, and those drugs are absolutely contraindicated with nitrate medications (used for angina and heart conditions) due to the risk of severe, potentially fatal hypotension, the same risk logically and pharmacologically applies to Horny Goat Weed. Anyone taking nitroglycerin, isosorbide mononitrate, isosorbide dinitrate, or similar nitrate medications should not take Horny Goat Weed.
What is the recommended dose of Horny Goat Weed?
A human pharmacokinetic and safety trial tested single oral doses of 370, 740, and 1,110 mg of a standardized Epimedium prenylflavonoid extract, finding it well tolerated with no adverse effects. A separate trial for bone health in postmenopausal women used a specific phytoestrogen extract providing 60 mg of icariin per day, combined with calcium. Doses vary considerably by intended use, and dosing should always be confirmed with a healthcare provider.
Can Horny Goat Weed help with bone health?
There is real human trial support: a 24-month randomized, double-blind, placebo-controlled trial found that Epimedium-derived phytoestrogen flavonoids had a beneficial effect on preventing bone loss in late postmenopausal women, alongside separate research showing icariin increases proliferation and differentiation of human osteoblasts.
Why is it called Horny Goat Weed?
The name traces to a Chinese legend in which a goat herder reportedly observed his goats becoming notably more sexually active after grazing on the plant. Its Chinese name, Yin Yang Huo, reflects the same traditional understanding, and it has been used in traditional Chinese medicine for impotence.
Does Horny Goat Weed interact with other erectile dysfunction medications?
This deserves caution given the shared mechanism. Since icariin and prescription PDE5 inhibitors (sildenafil, tadalafil, vardenafil) work on the same enzyme target, combining them is a reasonable theoretical concern for additive effects, and should be discussed with a healthcare provider rather than combined without guidance.
Primary Literature
Bibliography
↑
1.
Wang DX, Yang GL, Song XR, Kou SR. Determination of the pKa value of icariin and its content in the Chinese herb medicine epimedium grandiflorum morr. by capillary electrophoresis. Se Pu. 2001 Jan;19(1):64-67.
↑
2.
Chen XJ, Guo BL, Li SP, Zhang QW, Tu PF, Wang YT. Simultaneous determination of 15 flavonoids in Epimedium using pressurized liquid extraction and high-performance liquid chromatography. J Chromatogr A. 2007 Sep 7;1163(1-2):96-104.
↑
3.
Dell'Agli M, Galli GV, Dal Cero E, Belluti F, Matera R, Zironi E, Pagliuca G, Bosisio E. Potent inhibition of human phosphodiesterase-5 by icariin derivatives. J Nat Prod. 2008 Sep;71(9):1513-1517.
↑
4.
Dong XH, Gao WJ, Kong WN, Xie HL, Peng Y, Shao TM, Yu WG, Chai XQ. Neuroprotective effect of the active components of three Chinese herbs on brain iron load in a mouse model of Alzheimer's disease. Exp Ther Med. 2015 Apr;9(4):1319-1327.
PubMed PMID:25780429 →
↑
5.
Zhang G, Qin L, Shi Y. 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 Jul;22(7):1072-1079.
PubMed PMID:17419678 →
↑
6.
Yin XX, Chen ZQ, Dang GT, Ma QJ, Liu ZJ. Effects of Epimedium pubescens on proliferation and differentiation of human osteoblasts. Zhongguo Zhong Yao Za Zhi. 2005 Feb;30(4):289-291.
PubMed PMID:15724410 →
↑
7.
Wang Z, Zhang X, Wang H, Qi L, Lou Y. Neuroprotective effects of icaritin against beta amyloid-induced neurotoxicity in primary cultured rat neuronal cells via estrogen-dependent pathway. Neuroscience. 2007 Mar 30;145(3):911-922.
PubMed PMID:17321691 →
↑
8.
Yan FF, Liu Y, Liu YF, Zhao YX. Herba Epimedii water extract elevates estrogen level and improves lipid metabolism in postmenopausal women. Phytother Res. 2008 Sep;22(9):1224-1228.
PubMed PMID:18697183 →
↑
9.
Xie F, Wu CF, Lai WP, Yang XJ, Cheung PY, Yao XS, Leung PC, Wong MS. The osteoprotective effect of Herba epimedii (HEP) extract in vivo and in vitro. Evid Based Complement Alternat Med. 2005 Sep;2(3):353-361.
PubMed PMID:16136213 →
↑
10.
Pharmacokinetics research group. Pharmacokinetics of Prenylflavonoids following Oral Ingestion of Standardized Epimedium Extract in Humans. J Nat Prod. 2018.
PubMed PMID:30522143 →
↑
11.
Liao HJ, Chen XM, Li WG. Effect of Epimedium sagittatum on quality of life and cellular immunity in patients of hemodialysis maintenance. Zhongguo Zhong Xi Yi Jie He Za Zhi. 1995 Apr;15(4):202-204.
PubMed PMID:7647539 →
↑
12.
Tan X, Weng W. Efficacy of epimedium compound pills in the treatment of the aged patients with kidney deficiency syndrome of ischemic cardio-cerebral vascular diseases. Hunan Yi Ke Da Xue Xue Bao. 1998;23(5):450-452.
PubMed PMID:10682558 →
Additional Reference Literature
Wang C, Li Y, Wang Y. A review of pharmacological study on Epimedium grandiflorum Morr and its active constituents. Zhongguo Zhong Yao Za Zhi. 1998 Mar;23(3):183-185.
Tan HL, Chan KG, Pusparajah P, Saokaew S, Duangjai A, Lee LH, Goh BH. Anti-Cancer Properties of the Naturally Occurring Aphrodisiacs: Icariin and Its Derivatives. Front Pharmacol. 2016;7:191. DOI:10.3389/fphar.2016.00191 →
Wang Z, Xu G, Wang H, Zhan X, Gao Y, Chen N, Li R, Song X, Guo Y, Yang R, Niu M, Wang J, Liu Y, Xiao X, Bai Z. Icariside Ⅱ, a main compound in Epimedii Folium, induces idiosyncratic hepatotoxicity by enhancing NLRP3 inflammasome activation. Acta Pharm Sin B. 2020 Sep;10(9):1619-1633.