Benefits
Stress and Anxiety Relief
In a 60-day trial in 64 chronically stressed adults, 300 mg of KSM-66 twice daily cut perceived-stress scores by 44% (placebo 5.5%) and serum cortisol by 27.9% (placebo 7.9%). In a 60-day trial in 60 stressed adults, 240 mg of Shoden a day lowered anxiety scores more than placebo (41% vs 24%) and lowered morning cortisol.
Improved Sleep
In a 6-week trial in 150 healthy adults with unrefreshing sleep (144 finished), 120 mg of Shoden once daily raised self-rated sleep quality by 72% versus 29% with placebo, and wrist-monitor sleep efficiency, total sleep time and time to fall asleep also improved. A 90-day stress trial also reported better sleep-quality scores.
Testosterone and Muscle
In an 8-week trial in 57 young men doing resistance training, 300 mg of KSM-66 twice daily gave larger strength and muscle-size gains and a larger testosterone rise than placebo. In a crossover trial in aging, overweight men, Shoden raised salivary testosterone 14.7% more than placebo, but in a separate stress trial testosterone change did not differ from placebo.
Sperm Quality
In a 90-day pilot trial in 46 men with low sperm counts, 675 mg a day of KSM-66 raised sperm count, semen volume and sperm motility from baseline, with minimal change on placebo. It was small, did not measure pregnancies, and has not been confirmed in a larger trial cited here.
Cognitive Function
In a 90-day trial in 130 stressed but healthy adults aged 20 to 55, one 300 mg sustained-release capsule a day improved recall memory on a computerized test battery compared with placebo, along with lower stress scores. Effects in older adults or people with memory problems are not tested in the trials cited here.
Exercise Endurance
In a trial in 50 healthy athletic adults, 300 mg of KSM-66 twice daily raised VO2 max, a measure of aerobic fitness, more than placebo at 8 and 12 weeks (average gains about 5.7 vs 1.9 units at 12 weeks), and quality-of-life scores improved.
Mechanism of action
Adaptogenic Activity
Ashwagandha is thought to act on the hypothalamic-pituitary-adrenal (HPA) axis, the body's main stress-hormone system. In several trials cited here it lowered morning or serum cortisol, which fits this idea.
GABA-Mimetic Effects
Laboratory studies suggest withanolides may act on GABA receptors in the brain, which are involved in calming signals. This is a proposed mechanism from non-human research and has not been measured in the trials cited here.
Cognition Mechanism
Laboratory and animal studies suggest ashwagandha compounds may protect nerve cells and influence brain-derived neurotrophic factor (BDNF). This is a proposed mechanism; human trials cited here measured memory and stress scores, not these effects.
Hormonal Modulation
Ashwagandha may affect hormone levels. Trials cited here found rises in testosterone in men in two of three trials, and changes in DHEA-S, while an 8-week safety trial in healthy adults found no significant change in thyroid hormones.
Immunomodulation
Laboratory research suggests ashwagandha can influence immune cell activity. The clinical meaning is unclear, so people with autoimmune conditions or on immunosuppressant drugs should ask their doctor first.
Clinical trials
Single-center, randomized, double-blind, placebo-controlled trial of KSM-66 root extract, 300 mg twice daily for 60 days. Outcomes: Perceived Stress Scale, General Health Questionnaire-28, Depression Anxiety Stress Scale and serum cortisol. (Chandrasekhar et al. 2012, Indian J Psychol Med)
64 adults with a history of chronic stress.
Perceived-stress scores fell 44.0% with ashwagandha vs 5.5% with placebo, and serum cortisol fell 27.9% vs 7.9%; all stress scales improved significantly more than placebo. Adverse effects were mild and similar in both groups.
Randomized, double-blind, placebo-controlled trial of one 300 mg sustained-release root extract capsule a day for 90 days. Primary outcome: cognitive function on the CANTAB battery; secondary outcomes included stress, cortisol, sleep quality and happiness scores. Two authors were employees of ingredient companies. (Gopukumar et al. 2021, Evid Based Complement Alternat Med)
130 healthy but stressed adults aged 20 to 55 (125 completed).
Recall memory scores were higher and pattern-recall errors lower than placebo at day 90. Perceived-stress scores (13.0 vs 18.7), serum cortisol and sleep-quality scores were also better than placebo, and no adverse events were reported.
16-week randomized, double-blind, placebo-controlled crossover trial; each treatment phase lasted 8 weeks, with Shoden beads providing 21 mg of withanolide glycosides a day. Outcomes: fatigue, vigor, aging-male symptoms and salivary hormones. (Lopresti et al. 2019, Am J Mens Health)
57 overweight men aged 40 to 70 with mild fatigue (43 completed all 16 weeks).
Compared with placebo, ashwagandha gave an 18% greater rise in DHEA-S and a 14.7% greater rise in salivary testosterone. Fatigue, vigor and sexual well-being improved over time with both ashwagandha and placebo but did not differ significantly from placebo, and cortisol and estradiol did not differ.
Randomized, double-blind, placebo-controlled trial of 120 mg standardized ashwagandha extract (Shoden) once daily for 6 weeks, with sleep measured by questionnaire and wrist actigraphy. (Deshpande et al. 2020, Sleep Med)
150 healthy adults with non-restorative sleep (144 completed).
Self-rated sleep quality improved 72% with ashwagandha vs 29% with placebo. On actigraphy, sleep efficiency, total sleep time, time to fall asleep and wake time after sleep onset improved significantly more than with placebo. No treatment-related adverse events were reported.
60-day randomized, double-blind, placebo-controlled trial of 240 mg Shoden extract once daily. Outcomes: Hamilton Anxiety Rating Scale, DASS-21, and morning cortisol, DHEA-S and testosterone. (Lopresti et al. 2019, Medicine)
60 healthy adults with self-reported high stress.
Anxiety scores fell 41% with ashwagandha vs 24% with placebo (P = 0.040), while the DASS-21 difference was not significant (P = 0.096). Morning cortisol fell 23% (placebo rose 0.5%) and DHEA-S fell 8.2% (placebo rose 2.5%), both significantly more than with placebo. Testosterone rose in men over time, but the change did not differ significantly from placebo. No adverse events were reported.
Randomized, double-blind, placebo-controlled trial of KSM-66 root extract, 300 mg twice daily for 12 weeks. VO2 max was estimated with a 20-meter shuttle run test, and quality of life with the WHO questionnaire. (Choudhary et al. 2015, Ayu)
50 healthy athletic men and women (49 analyzed).
VO2 max rose more with ashwagandha than placebo at 8 weeks (4.91 vs 1.42) and 12 weeks (5.67 vs 1.86), and all quality-of-life domains improved more than with placebo by 12 weeks.
8-week randomized, double-blind, placebo-controlled trial of KSM-66 root extract, 300 mg twice daily, during a resistance-training program. Primary outcome: muscle strength. (Wankhede et al. 2015, J Int Soc Sports Nutr)
57 young men aged 18 to 50 with little resistance-training experience.
Compared with placebo, ashwagandha gave larger gains in bench-press strength (46.0 vs 26.4 kg) and leg-extension strength (14.5 vs 9.8 kg), larger arm and chest muscle size gains, a larger serum testosterone rise (96.2 vs 18.0 ng/dL) and a larger drop in body fat percentage.
90-day randomized, placebo-controlled pilot trial of KSM-66 root extract, 675 mg a day in three doses. Outcomes: semen parameters and serum hormones. (Ambiye et al. 2013, Evid Based Complement Alternat Med)
46 men with oligospermia (sperm count under 20 million/mL); 21 on ashwagandha, 25 on placebo.
In the ashwagandha group, sperm count rose 167%, semen volume 53% and sperm motility 57% from baseline, with minimal change on placebo, and hormone levels improved more than with placebo. Pregnancy outcomes were not measured.
Randomized, double-blind, placebo-controlled, parallel-group trial of ashwagandha root extract 300 mg twice daily for 8 weeks. Outcomes: blood counts, blood chemistry including liver tests, thyroid hormones, vital signs and adverse events. (Verma et al. 2021, Complement Ther Med)
80 healthy volunteers (40 men, 40 women).
No statistically significant changes or abnormalities were found in blood counts, blood chemistry, liver tests, thyroid hormones or vital signs, and no adverse events were reported. This was a short trial; rare cases of liver injury with ashwagandha have been reported outside trials.