Ashwagandha (Withania somnifera)

Best evidence: B- — Moderate evidence for Anxiety, cortisol & perceived stress

An adaptogenic herb with moderate evidence for reducing anxiety, stress, and cortisol — though effect sizes vary widely between studies.

Graded outcomes

What the evidence says

B-

Moderate evidence · Good evidence, with some gaps or inconsistency.

Effect size: SMD = −1.55 for anxiety and −1.75 for stress in one 12-study meta-analysis; cortisol reduction (MD = −2.58) consistently replicated; perceived-stress (PSS) findings are mixed — some meta-analyses report no significant effect.
Evidence base: Multiple meta-analyses, 9–15 RCTs each, ~500–1,000 total participants pooled; high statistical heterogeneity (I² = 83–94%), which lowers confidence in the precise effect size.
Population: Most trial participants had elevated baseline stress; effects in low-stress healthy populations are less studied.
Dosage / protocol: 125–600 mg daily of standardized root extract (≥5% withanolides is a common standardization), studied over 30–90 days.
Contraindications & cautions: Avoid in pregnancy, autoimmune conditions, and with thyroid medication (may affect thyroid hormone levels) — consult a doctor. Mild-to-moderate adverse events reported in some trials.

Citations

Compared with