Low testosterone levels can be problematic for men as they age. Fortunately, Mother Nature produces her own form of testosterone booster: the herb ashwagandha. Research published in the Journal of the International Society of Sports Nutrition tested 57 men between the ages of 18 and 50. They were divided into two groups—one was given 300 milligrams of the herbal extract twice a day for eight weeks; the other ingested a placebo for the same period. Both groups underwent supervised muscle training programs for the duration of the study.

The men that took the ashwagandha had significantly higher levels of circulating testosterone compared to the placebo group. The ashwagandha group also experienced an increase in muscle mass in the chest and arms, yielding an average arm muscle size of 8.6 centimeters, compared to the placebo group’s 5.3 centimeters.

Those men in the ashwagandha group also exhibited faster reductions of creatine kinase, a marker for the type of muscle fiber injury that occurs during strenuous exercise, following workouts.