The bottom line
The most consistent human evidence is for short-term (6-12 week) reductions in self-reported stress and anxiety and modest improvements in sleep, especially in people with insomnia. This rests on several small, mostly Indian RCTs of different branded root or root-plus-leaf extracts, pooled at low certainty[2, 5, 6]. At least one well-run trial found no effect on perceived stress[10]. Evidence for strength, testosterone, fertility and thyroid outcomes is limited to single small trials or observational data, and long-term efficacy and safety are unknown[2, 3, 13].
meta-analysisEvidence: moderate
Stress and anxiety (pooled)
12 RCTs, 1,002 participants aged 25-48; ashwagandha extract vs placebo; searches to Dec 2021
Ashwagandha was associated with significantly lower anxiety (SMD -1.55, 95% CI -2.37 to -0.74) and stress (SMD -1.75, 95% CI -2.29 to -1.22) than placebo. Dose-response analysis suggested a favourable effect on stress at 300-600 mg/day.[5]
Limitations: Very high heterogeneity (I² 93.8% and 83.1%). The authors rated the certainty of evidence as low and called for higher-quality trials.
RCTEvidence: limited
Stress and anxiety
n=64 adults with chronic stress; 60 days; 300 mg high-concentration root extract twice daily vs placebo; single centre, India
All stress scales improved significantly more than with placebo, and serum cortisol fell more (P=0.0006). Adverse effects were mild and similar between groups.[7]
Limitations: Small single-centre trial of a branded extract; short duration.
RCTEvidence: limited
Stress and anxiety
n=60 stressed healthy adults; 60 days; 240 mg/day standardised extract (Shoden, a root-and-leaf extract per ODS) vs placebo
HAM-A anxiety scores fell significantly versus placebo (P=.040), while the DASS-21 change was not significant (P=.096). Morning cortisol and DHEA-S fell more than with placebo.[8, 2]
Limitations: Small sample. The extract includes leaf. The authors called for larger and more diverse trials.
RCTEvidence: limited
Stress and fatigue (null primary outcome)
Overweight/mildly obese adults aged 40-75 with high stress and fatigue; 12 weeks; 200 mg root extract (Witholytin) twice daily vs placebo (ODS reports n=120)
Perceived stress (the primary outcome) did not improve more than with placebo (p=0.867). Fatigue scores and heart-rate variability improved versus placebo, and free testosterone and LH rose in men.[10, 2]
Limitations: A negative result on the primary outcome; positive findings are secondary outcomes only. One author directs a contract research organisation funded by nutraceutical companies.
meta-analysisEvidence: moderate
Sleep (pooled)
5 RCTs, 400 adults; ashwagandha extract vs placebo
There was a small but significant effect on overall sleep (SMD -0.59, 95% CI -0.75 to -0.42). The effect was larger in adults with insomnia, at doses of at least 600 mg/day, and with at least 8 weeks of use. No serious side effects were reported.[6, 2]
Limitations: Moderate heterogeneity (I² 62%). All included trials were from India (per ODS). Data on serious and long-term adverse effects are limited.
RCTEvidence: limited
Sleep / insomnia
n=80 (40 healthy, 40 with insomnia); 8 weeks; root extract (ODS: KSM-66, 300 mg twice daily) vs placebo
Sleep parameters improved, more so in the insomnia group. Sleep-onset latency and sleep efficiency were the most improved measures.[9, 2]
Limitations: Small sample of a single branded extract. The authors say further trials are needed before the results can be generalised.
RCTEvidence: limited
Muscle strength (resistance training)
n=57 young men new to resistance training; 8 weeks; 300 mg root extract twice daily vs starch placebo
Bench-press and leg-extension strength, arm and chest muscle size, and serum testosterone rose more than with placebo, and body-fat percentage fell more.[11]
Limitations: A single small, short trial in men only.
RCTEvidence: limited
Male hormones and vitality
Crossover; 57 enrolled overweight men aged 40-70 with mild fatigue; 8 weeks each arm; Shoden extract (21 mg withanolide glycosides/day) vs placebo
DHEA-S rose 18% and testosterone 14.7% more than with placebo. Fatigue, vigour, sexual well-being, cortisol and estradiol did not differ significantly between groups.[12]
Limitations: Small sample with dropouts (43 completed). Hormone changes did not translate into symptom differences.
systematic reviewEvidence: preliminary
Male infertility (semen parameters)
4 clinical trials (5 publications): 4 observational and 1 RCT; meta-analysis of observational before/after data only
Sperm concentration, semen volume and motility improved versus pre-treatment, and hormone profiles improved. No adverse effects were reported.[13, 3]
Limitations: Only one RCT was available, so no RCT meta-analysis was possible. The authors say the data are too limited to be robust.
RCTEvidence: preliminary
Thyroid function (subclinical hypothyroidism)
n=50 adults with TSH 4.5-10 μIU/L; 8 weeks; 600 mg/day root extract vs starch placebo; single centre, Varanasi
TSH, T3 and T4 changed significantly compared with placebo (TSH fell, T3 and T4 rose), moving toward normal ranges.[14, 2]
Limitations: Pilot-sized, single-centre, short trial. The finding also implies a possible thyroid-stimulating effect that may matter as a safety issue (see safety).
These studies explain possible mechanisms. They do not show the same effect in people.