Ashwagandha (Withania somnifera) is an adaptogenic herb that—based on multiple randomized trials and reviews—can reduce stress, anxiety and morning cortisol; improve sleep quality and some measures of cognition; enhance physical performance, muscle strength and recovery; raise testosterone and improve semen parameters in some infertile men; help lower blood sugar and improve lipid markers modestly; and shows antioxidant, anti-inflammatory and possible cardioprotective and anticancer effects in preliminary studies—however most results come from small or short trials, and safety concerns (drug interactions, effects on thyroid/autoimmune conditions, and avoidance in pregnancy/breastfeeding or before surgery) mean people should consult a clinician