Ashwagandha is a traditional Indian medicine (Ayurveda) that is known to be associated with male virility and vitality; a common supplement to recommend to men that are feeling past their prime and a traditional medicine with a surprisingly large amount of evidence overall. It does seem to have some anti-stress effects due to the having the properties of an adaptogen.
Among the adaptogens and traditional medicine, however, ashwagandha is one of the few associated with masculinity. Since anything that can be named a testosterone booster gets praise faster than it gets research, many people are wondering whether ashwagandha can increase testosterone or whether it is overhyped.
When it comes to the topic of testosterone, the first study to find an effect was one in male rats where an increase was seen. When later tested in men suffering some degree of infertility or low fertility, improvements in sperm quality came alongside subtle boosts in testosterone around the range of 14-40% or 10-22% higher than before the study.
While a promising supplement for fertility, it should be stated that supplements that can provide antioxidant support to the testicles are at times associated with an increase in testosterone only in the infertile but not otherwise fertile men (Vitamin E and CoQ10 as examples) while other profertility drugs, such as D-Aspartic acid, can be confused with testosterone boosting supplements when the benefits seen in infertile men are erronously extrapolated.
However, despite all that, at least one study has found a mild increase in testosterone in otherwise healthy men subject to weight training by 15%. It is not likely that a 15% increase in testosterone will result in major changes to the muscularity of the body, but an earnest increase in testosterone in healthy young men by a dietary supplement is quite rare.
While it is more likely a profertility agent, we cannot deny a possibility that ashwagandha could increase testosterone. However, evidence at this time is quite limited