Ashwagandha: the best-studied adaptogen with real stress-and-sleep evidence

Ashwagandha (Withania somnifera) has the strongest RCT base of any "adaptogen", which is itself a low bar, but the evidence for ashwagandha specifically is more developed than for rhodiola, ginseng, or schisandra.

What the trials show#

Several dozen RCTs have tested ashwagandha for stress, anxiety, sleep, and exercise performance. The pattern is moderately consistent:

Stress and anxiety. A 2022 meta-analysis (Akhgarjand et al.) pooled 12 RCTs (1,002 participants) in adults with stress or anxiety. Statistically significant reductions in subjective stress and anxiety scales versus placebo, with large effect sizes, though the authors rated the overall certainty of the evidence as low. Most trials used KSM-66 standardised root extract at 300–600 mg/day for 8 weeks.

Cortisol. Some trials also measure serum cortisol, but the meta-analysis cited on this page covers anxiety and stress scores rather than cortisol, so we don't give an effect size here.

Sleep. Smaller trials suggest modest improvements in sleep quality scales, possibly via the stress/cortisol pathway. Effects are not on par with established hypnotics.

Exercise performance. Several trials in resistance-training contexts report modest improvements in strength and recovery. The mechanism is unclear.

Testosterone. Some trials in men with subfertility or stress report modest increases in serum testosterone. The effect is small and the populations are specific.

Trial quality concerns#

Several caveats apply:

• Many trials originate from a small number of Indian research groups, sometimes with industry funding
• Standardisation between products varies substantially
• Trial duration is typically 8–12 weeks; long-term effects less studied
• Outcomes are predominantly subjective scales

These don't invalidate the evidence but should temper enthusiasm.

The standardisation problem#

Ashwagandha is sold in many forms with very different active-compound content:

• KSM-66 (standardised root extract, 5% withanolides): the most-studied form in modern trials
• Sensoril (standardised root + leaf extract, 10% withanolides): used in some trials
• Generic root powders: withanolide content highly variable; quality varies dramatically
• Whole-plant extracts — different active profile from root-only extracts

For the trial-supported effects, KSM-66 or Sensoril at standardised doses is the version most aligned with the evidence base.

What gets overstated#

• "Treats depression." Modest effects on mood scales in stressed adults; not equivalent to first-line depression treatment.
• "Boosts testosterone significantly." Modest effects in specific populations; not equivalent to clinical TRT in indicated patients.
• "Eliminates anxiety." Real anxiolytic effects but not a substitute for evidence-based anxiety treatment in clinical anxiety disorders.

Side effects and interactions#

Ashwagandha is generally well-tolerated short-term. Reported issues:

• GI symptoms (nausea, loose stools) at higher doses
• Drowsiness in some users
• Liver injury: a small but real signal in case reports; several cases of hepatotoxicity reported in the literature. The risk is uncommon but real.
• Thyroid effects: ashwagandha can modestly raise T4; problematic in hyperthyroidism, potentially helpful in subclinical hypothyroidism (don't self-manage)
• Pregnancy: traditionally considered abortifacient at high doses; avoided in pregnancy
• Autoimmune disease: theoretical immune-stimulating effects make it cautious in conditions like Hashimoto's or lupus
• Sedating medication interactions — additive effect

UK regulatory framing#

Sold as a food supplement. Not regulated as a medicine. The hepatotoxicity case reports have prompted regulatory scrutiny in some countries; UK FSA awareness is growing.

What we'd actually say#

Ashwagandha is one of the better-evidenced supplements for stress and anxiety symptoms in healthy or mildly stressed adults. The trial effects are modest, real, and reasonably replicated.

For someone with mild stress-related symptoms, an 8-week trial of standardised KSM-66 at 300–600 mg/day is a reasonable experiment with low risk.

For someone with diagnosed anxiety disorder, depression, or insomnia, the NICE first-line treatments are more evidenced and should come first. Ashwagandha is an adjunct at most.

The liver injury signal is real and uncommon but worth knowing about. If you experience GI symptoms, dark urine, jaundice, or unusual fatigue while taking it, stop and seek clinical input.

When to talk to a clinician#

• Diagnosed anxiety, depression, or insomnia: establish first-line treatment
• Thyroid disorders, particularly hyperthyroidism
• Autoimmune disease
• Liver disease or abnormal liver function tests
• On sedating medications, thyroid medications, or immunosuppressants
• Pregnancy or trying to conceive
• Any unexpected symptoms (jaundice, dark urine, persistent GI symptoms): Yellow Card reportable