The participants took 200 mg of ashwagandha extract or a placebo twice daily.

Testosterone increased by 18% in the ashwagandha group but decreased by 11% in the placebo group.

The study assessed an extensive number of outcomes to determine the safety of ashwagandha. Blood lipids, blood parameters (e.g., serum platelets), glycemic control, kidney function tests, liver function tests, and thyroid hormones did not meaningfully differ between the groups. No adverse events were reported.

The manufacturer of the supplement funded the study and employed several of the researchers.

Ashwagandha may increase testosterone, but is it safe? Original paper