Ashwagandha KSM-66®

A pilot study using KSM-66® in oligospermic (subfertile) men found significant improvements in sperm concentration (167%), motility (57%), and semen volume (53%) alongside a 17% increase in serum testosterone over 90 days. These results are specific to men with fertility issues — effects in healthy men would likely be smaller.

In a crossover trial of 57 overweight men aged 40–70, salivary testosterone was 14.7% higher during 8 weeks on ashwagandha (Shoden extract) than during 8 weeks on placebo (p = .010), and salivary DHEA-S 18% higher. Testosterone was measured in saliva, not blood. The study was funded by the extract’s manufacturer. For KSM-66®, the extract in RBRN, see the Wankhede 2015 and Mutha 2025 trials on this page.

In an 8-week randomized, double-blind trial, 100 healthy men aged 30–50 (93 analysed) took 600mg a day of KSM-66® or placebo. Total testosterone rose 70 ng/dL on ashwagandha and fell 50 ng/dL on placebo (difference 120 ng/dL, p = .012). The paper also reports gains in semen volume, sperm count per ejaculate, sexual desire scores, and the orgasm and desire domains of the IIEF; other IIEF domains did not differ from placebo. The extract was supplied by its manufacturer; the study received no specific grant.

In a 12-week trial of 120 stressed, overweight adults aged 40–75, 400mg a day of a different ashwagandha extract (Witholytin®) raised free testosterone and luteinizing hormone in the men compared with placebo. Total testosterone did not differ from placebo (p = .42). The trial was funded by the extract’s manufacturer.

In a 60-day randomized, double-blind trial of 64 chronically stressed adults (41 men, 23 women) taking 600mg a day of KSM-66®, serum cortisol fell about 28% from baseline, against about 8% on placebo. This cortisol-lowering effect is one of ashwagandha’s most consistent findings across studies. A 2026 meta-analysis also found lower cortisol with ashwagandha (SMD −1.18), though the pooled trials varied widely.

An 8-week randomized, double-blind trial found that the ashwagandha group achieved 74% greater bench press gains, 48% greater leg extension gains, and 62% greater muscle size gains compared to placebo. These are relative comparisons between groups — not absolute increases. The ashwagandha group also showed reduced exercise-induced muscle damage. Testosterone rose 96 ng/dL on KSM-66® (600mg a day) versus 18 ng/dL on placebo over 8 weeks (p = .004). 57 men enrolled (50 analysed), average age 28; both groups followed the same resistance-training program. The extract was supplied by its manufacturer; the authors declared no conflicts.

A systematic review found consistent evidence for ashwagandha’s ability to reduce stress and anxiety symptoms, with effects occurring within weeks of supplementation. Two 2025-2026 meta-analyses now pool this evidence: ashwagandha significantly reduced anxiety, stress, and depression symptoms across dozens of randomized trials.