Quick Facts
- Evidence LevelStrong
- Research Dosages300–600 mg/day (root extract)
- Effect Size (SMD)-1.55 to -6.87
- Time to Effect6–8 weeks (median)
- Cortisol ReductionMD = -2.58 vs placebo
- Safety vs PlaceboNo significant difference
Key Studies
Ashwagandha has an unusually robust evidence base for an herbal supplement — multiple independent meta-analyses all point in the same direction.
Effects of ashwagandha on mental health in adults
The largest meta-analysis to date. Found ashwagandha significantly reduced anxiety (SMD = -6.87, 95% CI: -8.77 to -4.97), stress (SMD = -5.88), and depression (SMD = -5.68). Critically, this study confirmed a dose-response relationship — higher doses produced greater stress reduction (coefficient = 0.005, p = 0.031).[1]
Ashwagandha supplementation for anxiety and stress management
Found ashwagandha significantly reduced anxiety (SMD = -1.55, 95% CI: -2.37 to -0.74) and stress (SMD = -1.75, 95% CI: -2.29 to -1.22) compared to placebo. Participants were aged 25–48 across 12 trials. Evidence certainty was rated as low, primarily due to heterogeneity in extract types and dosages.[2]
Ashwagandha for mental health in individuals with mental disorders
Confirmed ashwagandha's effectiveness for anxiety, depression, stress, and sleep quality in people with diagnosed mental health conditions. Bayesian analysis specifically confirmed the anxiety findings, adding statistical rigor. No significant safety or tolerability differences from placebo were found.[3]
Effects of Ashwagandha on stress and anxiety
Found significant reductions in Perceived Stress Scale (MD = -4.72), Hamilton Anxiety Scale (MD = -2.19), and serum cortisol (MD = -2.58) compared to placebo. The cortisol reduction provides a biomarker-level confirmation of the self-reported anxiety improvements. Only mild-to-moderate adverse events were reported.[4]
How Ashwagandha Reduces Anxiety
Multiple mechanisms have been identified, supported by both human trial biomarkers and preclinical research:
- Cortisol reduction: The Arumugam et al. meta-analysis confirmed a significant decrease in serum cortisol (MD = -2.58).[4] Chronically elevated cortisol is a hallmark of stress-related anxiety. Ashwagandha appears to modulate the HPA (hypothalamic-pituitary-adrenal) axis, the body's central stress response system.
- GABAergic activity: Withanolides — the active compounds — demonstrate GABA-mimetic properties in animal models. GABA is the brain's primary inhibitory neurotransmitter and the target of conventional anxiolytics like benzodiazepines.
- Serotonin modulation: Some evidence suggests ashwagandha influences serotonin receptor activity (5-HT1A), which is also the target of buspirone, a prescription anxiolytic.
- Anti-inflammatory effects: Withanolides have demonstrated anti-inflammatory properties. Neuroinflammation is increasingly recognized as a contributor to anxiety disorders.
Dosages Used in Research
| Extract | Dosage | Notes |
|---|---|---|
| KSM-66 (root) | 300–600 mg/day | Most studied. Full-spectrum root extract standardized to 5% withanolides. Median dose in meta-analyses: 600 mg/day. |
| Sensoril (root + leaf) | 125–250 mg/day | Higher withanolide concentration. Lower effective dose. |
| Generic root extract | 300–1,000 mg/day | Variable standardization. Used in older studies. |
The 2026 dose-response meta-analysis confirmed that higher doses produce greater effects, with 600 mg/day being the most commonly effective dose across trials. Median follow-up across meta-analyses was 8 weeks.[1]
Safety Considerations
- Well-tolerated: The Marchi et al. meta-analysis found no significant safety differences between ashwagandha and placebo across 14 studies.[3] Only mild-to-moderate side effects were reported (GI discomfort, drowsiness).
- Thyroid effects: Ashwagandha can increase thyroid hormones (T3 and T4). Avoid in hyperthyroidism; monitor if on thyroid medication.
- Liver concerns: Rare cases of liver injury reported. Those with liver disease should avoid use.
- Pregnancy: Not recommended — insufficient safety data; some traditional texts classify it as an abortifacient.
- Drug interactions: May potentiate sedatives, immunosuppressants, thyroid medications, and blood sugar-lowering drugs.
- Autoimmune conditions: As an immunomodulator, it may stimulate immune activity. Generally not recommended for lupus, RA, or MS.
The Bottom Line
Ashwagandha has the strongest evidence of any supplement for anxiety. Four independent meta-analyses show consistent, significant reductions in anxiety scores, with effect sizes (SMD -1.55 to -6.87) substantially larger than those seen for magnesium, omega-3, or L-theanine.
The evidence is further strengthened by:
- A confirmed dose-response relationship — more isn't always better with supplements, but in this case higher doses do correlate with greater benefit
- Biomarker confirmation — serum cortisol reductions provide objective evidence beyond self-reported questionnaires
- Bayesian analysis in one meta-analysis adding statistical robustness
- No significant safety differences from placebo across multiple reviews
The main caveats are that evidence certainty is often rated "low" due to heterogeneous extract types, and long-term data beyond 12 weeks remains limited. The safety profile is favorable for most adults, but those with thyroid conditions, liver disease, autoimmune conditions, or who are pregnant should avoid use.
References
- Alsanie SA, Alhodieb FS, Askarpour M. "Effects of ashwagandha (Withania somnifera) on mental health in adults: A systematic review and dose-response meta-analysis of randomized controlled trials." Complement Ther Med. 2026. PubMed
- Akhgarjand C, et al. "Does Ashwagandha supplementation have a beneficial effect on the management of anxiety and stress?" Phytother Res. 2022;36(11):4115-4124. PubMed
- Marchi M, et al. "The effect of Withania somnifera (Ashwagandha) on mental health symptoms in individuals with mental disorders." BJPsych Open. 2025. PubMed
- Arumugam V, et al. "Effects of Ashwagandha (Withania Somnifera) on stress and anxiety: A systematic review and meta-analysis." Explore (NY). 2024. PubMed
- Fatima K, et al. "Safety and efficacy of Withania somnifera for anxiety and insomnia: Systematic review and meta-analysis." Hum Psychopharmacol. 2024;39(6):e2911. PubMed