What clinical evidence exists for ashwagandha, maca or horny goat weed increasing semen volume?
Executive summary
Clinical evidence that any of the three herbs reliably increases semen volume in humans is limited but non‑zero: multiple randomized and controlled trials plus a small pilot trial report increased semen volume with ashwagandha in infertile and healthy men [1] [2] [3], maca trials report improvements in sperm concentration but generally not volume [4], and horny goat weed (Epimedium) has promising preclinical/animal data with scarce, low‑quality human data on semen volume [5] [6]. All three ingredients suffer from heterogeneous products, small sample sizes, short follow‑up, and unresolved safety/standardization questions that weaken claims of broad, clinically meaningful benefit [6] [7].
1. Ashwagandha: the strongest human signals, but from small and selective trials
Ashwagandha has the most direct human data showing increases in semen volume: a 90‑day pilot randomized study in oligospermic men reported a 53% mean rise in semen volume alongside large gains in sperm count and motility [1], and a later prospective randomized double‑blind trial reported significant improvement in semen volume (p = 0.005) as part of multiple improved semen parameters after eight weeks of root extract in healthy men [2] [3]. Systematic reviews and multiple small trials summarized in the literature suggest ashwagandha may improve semen quality by reducing oxidative stress and modulating hormones in infertile men [8] [1]. These results are encouraging but derive from modest sample sizes, mixed populations (infertile vs. healthy), varied extract types/doses, and relatively short treatment windows, limiting generalizability and precluding firm conclusions about routine use.
2. Maca: some randomized trials improve sperm concentration, not volume
Maca (Lepidium meyenii) shows human trial evidence for improving sperm concentration and sometimes erectile parameters, but randomized data explicitly reporting increased semen volume are lacking; a 2020 randomized placebo‑controlled trial in infertile men found improved sperm concentration after 12 weeks of 2 g/day maca but did not change sperm motility or semen volume [4]. Reviews of common ED ingredients list maca among agents with possible benefit for libido and some semen parameters, but the pattern across trials is an effect on concentration or subjective sexual function rather than on ejaculate volume per se [6]. Thus maca’s clinical footprint supports fertility‑related endpoints selectively, not a reproducible volume increase.
3. Horny goat weed (Epimedium): biologic plausibility but few human volume data
Epimedium extracts (notably icariin) produce erectogenic and neurotrophic effects in vitro and in animal models, and multiple preclinical studies suggest mechanisms—PDE‑5 inhibition, nitric oxide modulation—relevant to sexual function [6] [5]. Human clinical trials directly measuring semen volume after horny goat weed are sparse or absent in the cited literature; most positive signals come from animal work or studies of erectile function rather than ejaculate volume [5] [6]. Supplement marketing and product analyses routinely include Epimedium for “semen enhancement,” but that reflects formulation trends more than robust clinical proof for increased semen volume [7].
4. Why the evidence remains provisional: method, product, and safety caveats
Across the three herbs the evidence base is heterogeneous: small sample sizes, short durations, trials concentrated in infertile men, inconsistent dosing and extract standardization, and frequent co‑administration with other ingredients in commercial products—factors that make causality and dose‑response uncertain [1] [6] [7]. Safety profiles and long‑term effects are under‑studied; horny goat weed in particular can carry risks and product quality varies widely, so consumer formulations may not match clinical trial preparations [6] [7]. Recent trials (e.g., the 8‑week ashwagandha RCT) strengthen the signal for ashwagandha but do not remove the need for larger, independently replicated trials with standardized extracts and clinically relevant endpoints [2] [3].
5. Bottom line and how to interpret the current literature
The best available clinical evidence supports that ashwagandha can increase semen volume in certain trial populations (notably infertile men) and has multiple small RCTs/pilot studies reporting such effects [1] [2] [3], whereas maca has randomized data improving sperm concentration but not volume [4], and horny goat weed has plausible mechanisms and animal evidence but little direct human proof for volume increases [5] [6]. Given methodological limits, claims that any of these herbs will reliably boost semen volume in the general population should be treated as provisional pending larger, standardized clinical trials; product variability and safety considerations further counsel caution [6] [7].