Ashwagandha: The Complete Guide to Stress, Cortisol & Performance

Ashwagandha (Withania somnifera) is an evergreen shrub native to India, the Middle East, and parts of Africa. It has been used in Ayurvedic medicine for over 3,000 years as a 'rasayana' — a rejuvenating tonic. The name 'ashwagandha' comes from Sanskrit, meaning 'smell of the horse,' referring both to its unique smell and the traditional belief that it imparts the vigor and strength of a stallion. Ashwagandha is classified as an adaptogen — a natural substance that helps the body adapt to stress and maintain homeostasis. Its primary active compounds are withanolides, a group of steroidal lactones concentrated in the root. Modern research has validated many traditional uses, with over 600 published studies examining its effects on stress, anxiety, cognitive function, testosterone, athletic performance, and sleep quality.

Ashwagandha's most well-documented benefit is its ability to reduce cortisol levels and subjective stress. Cortisol is the body's primary stress hormone — while essential for survival, chronically elevated cortisol contributes to anxiety, weight gain (particularly abdominal fat), muscle breakdown, impaired immune function, and disrupted sleep. A landmark study published in the Indian Journal of Psychological Medicine found that 300mg of KSM-66 ashwagandha extract twice daily reduced serum cortisol levels by 30.5% compared to placebo over 60 days. Participants also reported a 69% reduction in anxiety and insomnia scores. Multiple subsequent studies have confirmed these findings, with cortisol reductions ranging from 14% to 32% across different populations and dosing protocols.

Several studies have demonstrated ashwagandha's ability to increase testosterone levels in men. A study of overweight men aged 40–70 found that 600mg of KSM-66 daily for 8 weeks increased testosterone by 15% compared to placebo. Another study in infertile men found that 5g of ashwagandha root powder daily for 3 months increased testosterone by 10–22% and improved sperm count by 167% and sperm motility by 57%. The mechanism appears to involve both direct effects on the testes and indirect effects through cortisol reduction (high cortisol suppresses testosterone production). It's important to note that the testosterone-boosting effects are most pronounced in men with suboptimal levels or high stress — ashwagandha is unlikely to push testosterone above normal physiological ranges.

Ashwagandha has shown promising results for athletic performance and body composition. A study of healthy men engaged in resistance training found that 300mg of KSM-66 twice daily for 8 weeks resulted in significantly greater increases in muscle strength (bench press: 44 kg vs. 26.4 kg increase) and muscle size compared to placebo. The ashwagandha group also experienced greater reductions in exercise-induced muscle damage and body fat percentage. Another study in elite cyclists found that 500mg of aqueous root extract twice daily for 8 weeks improved VO2max by 12.5% and time to exhaustion. The mechanisms likely involve cortisol reduction (less muscle breakdown), improved recovery, and enhanced mitochondrial function.

The two most studied and standardized ashwagandha extracts are KSM-66 and Sensoril. KSM-66 is a full-spectrum root extract standardized to 5% withanolides. It's produced using a proprietary extraction process that preserves the natural balance of active compounds. KSM-66 is the most clinically studied ashwagandha extract, with over 24 gold-standard clinical trials. The standard dose is 300mg twice daily (600mg total). Sensoril is extracted from both roots and leaves and is standardized to 10% withanolides. Because of the higher withanolide concentration, effective doses are lower (125–250mg). Sensoril tends to be more calming and is often preferred for stress and sleep, while KSM-66 is considered more energizing and is preferred for performance and testosterone. Both are excellent choices — the best one depends on your primary goals.