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Epimedium and Icariin: What PDE5 Inhibition Means
Epimedium icariin is the main compound in horny goat weed, and lab work suggests it may mildly inhibit PDE5, the enzyme that prescription sildenafil and tadalafil block. Mild lab inhibition is not drug-level action. Stallion Power lists horny goat weed extract last in its blend, at 5 mg or less per gummy.
Written by the Stallion Power label deskUpdated · 4 min read
Definitions01
What are epimedium and icariin?
Epimedium is the plant genus behind horny goat weed. Icariin is its best-studied compound (MSKCC, Epimedium (horny goat weed)).
Memorial Sloan Kettering says icariin promotes estrogen biosynthesis in vitro and may mildly inhibit PDE5 (MSKCC, Epimedium (horny goat weed)). The same source calls the overall evidence limited.
Mechanism02
What does PDE5 inhibition mean?
PDE5 is an enzyme. Blocking it helps blood vessels stay relaxed, which is how prescription sildenafil works (MedlinePlus, Sildenafil).
The key word for icariin is "mildly", and the findings are from lab work. A mild effect in a dish is far from a prescription dose in a man.
| Point | Sildenafil | Icariin |
|---|---|---|
| Status | Prescription drug | Plant compound in supplements |
| Evidence | Approved after testing | Limited, mostly lab-based |
| Nitrates | Must never be combined (MedlinePlus, Sildenafil) | Ask a doctor first |
The label03
How much epimedium is in a Stallion Power gummy?
At most 5 mg of horny goat weed extract, and the label does not say how much of that is icariin.
The extract is listed ninth of nine, after the 5 mg caffeine. This is our arithmetic from the label order, not a lab test. The table below shows each line's ceiling.
| Place | Label line | Most it can weigh | Why |
|---|---|---|---|
| 1 | Muira puama extract | At most about 77 mg | The first line can be at most everything except the caffeine: 77 mg. |
| 2 | Maca extract | At most about 38 mg | Two lines at least this heavy, so at most half of 77 mg. |
| 3 | Catuaba extract | At most about 25 mg | Three lines at least this heavy: at most a third of 77 mg. |
| 4 | Green tea extract | At most about 19 mg | Four lines at least this heavy: at most a quarter of 77 mg. |
| 5 | Caffeine | 5 mg | Printed on the label: 5 mg. |
| 6 | Ashwagandha | At most about 5 mg | Listed after the 5 mg caffeine, so it cannot weigh more than that. |
| 7 | L-arginine | At most about 5 mg | Listed after the 5 mg caffeine, so it cannot weigh more than that. |
| 8 | Tribulus terrestris | At most about 5 mg | Listed after the 5 mg caffeine, so it cannot weigh more than that. |
| 9 | Horny goat weed extract | At most about 5 mg | Listed last, so it cannot weigh more than the caffeine. |
Lines 1-4 must add up to 77 mg minus nothing else: 82 mg total, less 5 mg caffeine, less at most 20 mg for lines 6-9, leaves at least 57 mg for lines 1-4. This is our arithmetic from the label order, not a lab test. The label also says the blend is equivalent to about 567 mg of dry powders, which describes the starting plant material, not the finished amounts.
Stallion Power: from $49 a bottle30 gummies · 2, 3 or 6 bottles · free shipping on 3 or 6 · 60-day guarantee
See packsCaution04
Why does the nitrate warning still matter?
Because the safe approach with any possible PDE5 effect is to ask first, especially with nitrate heart medicine.
Nitrates plus sildenafil can drop blood pressure dangerously (MedlinePlus, Sildenafil). Nobody has measured what a 5 mg share of an extract does, so the cautious route is a pharmacist question. Our hidden drug guide explains why labels alone cannot settle it.
Next steps05
What is a sensible way to use this information?
Treat icariin as an interesting lab finding, not a promise.
See a doctor about erection changes, and keep taking prescribed medicine as directed. The horny goat weed page has the full profile.
Want to try Stallion Power? Both packs ship free, and both come with the 60-day guarantee (all bottles returned, even empty ones).
Prices on the sales page, October 18, 2026 (Stallion Power sales page). Check your medicines with your doctor first.
FAQ06
Epimedium and icariin questions
What is icariin?
Icariin is a major compound in Epimedium plants, also called horny goat weed. Lab work suggests it may mildly inhibit PDE5 (MSKCC, Epimedium (horny goat weed)). No human trial shows that a gummy with a small share does the same.
Is epimedium the same as horny goat weed?
Yes. Horny goat weed is the common name for Epimedium species. Stallion Power labels it Horny Goat Weed Extract and lists it ninth in the blend.
Does icariin work like sildenafil?
No. Sildenafil is a tested prescription drug (MedlinePlus, Sildenafil). Icariin showed only mild PDE5 inhibition in lab work, and its evidence in men is limited (MSKCC, Epimedium (horny goat weed)).
Who wrote this07
Written and reviewed by
Pages built from the label, the sales page and linked NIH, FDA, CDC, FTC and peer-reviewed sources.
Last updated . Read our editorial standards and how we check reviews. This website is run by Stallionpowermen, a USA stocking retailer for Stallion Power, not by the manufacturer or the distributor. We are paid a commission when you buy through our order links.
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