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Evidence Lab

Ashwagandha

Ashwagandha may modestly improve stress or sleep in some adults, while exercise-performance findings remain heterogeneous. Short-term use appears reasonably tolerated for many adults, but thyroid, autoimmune, pregnancy, liver and medication contexts require caution.

Evidence rating: Emerging / Mixed

Published 8/14/2026 | Last reviewed 8/14/2026

Overview

Ashwagandha (Withania somnifera) is an Ayurvedic botanical commonly marketed for stress, sleep, cognition, testosterone and athletic performance. Trials use different root or root-and-leaf extracts with different withanolide profiles, so products are not interchangeable. For exercise, a 2026 systematic review and three-level meta-analysis found an average positive effect across heterogeneous performance outcomes, but the prediction interval crossed zero and certainty varied by domain. The most consistent signal was for aerobic-endurance outcomes, while strength and other performance claims remain less certain. Separate meta-analysis suggests a small sleep benefit, especially in people with insomnia and with longer or higher-dose protocols. Safety deserves equal weight. NCCIH states that short-term use up to about three months may be safe for many adults, but longer-term safety is uncertain. Rare liver injury has been reported, and ashwagandha is not recommended in pregnancy, breastfeeding, before surgery, or in people with autoimmune or thyroid disorders without clinical guidance.

Common use

Optional short-term use for stress or sleep support, with exercise-performance use treated as emerging rather than established.

Common forms

Root powders, standardized root extracts and root-and-leaf extracts with variable withanolide content. Product standardization differs substantially.

Practical notes

Do not assume that milligram doses from one extract translate directly to another. Use a transparent standardized product and monitor sleepiness, gastrointestinal symptoms and any signs of liver injury. Last evidence review: 14 August 2026.

Claim-level evidence

Emerging / Mixed

Ashwagandha may improve some exercise-performance outcomes, but the evidence is heterogeneous and does not predict benefit for every athlete.

Population: Mostly young adults and athletes in short-term randomized trials.

Treat performance use as promising but not established across all domains.

Limitations: The 2026 meta-analysis found a positive mean effect but a prediction interval crossing zero, with heterogeneity across outcomes and products.

Moderate

Some ashwagandha preparations may improve sleep, particularly in people with insomnia.

Population: Adults with and without insomnia.

Sleep may be a more defensible use than generic performance enhancement when the person tolerates the supplement and has no contraindication.

Limitations: Studies are small and use varied preparations; long-term safety is uncertain.

Insufficient

Ashwagandha should not be presented as a proven testosterone or strength booster for all users.

Population: Healthy adults and athletes.

Avoid extrapolating limited endocrine or individual-trial findings into universal claims.

Limitations: Products, populations, outcomes and study quality vary substantially.

Dosing context

  • Exercise research context - Many trials use standardized extracts around 500-600 mg/day, but formulations and withanolide content differ. - Often split or taken once daily depending on the product and protocol. - Commonly 6-12 weeks in exercise trials.This range is study context, not a universal dose; product equivalence cannot be assumed.
  • Sleep research context - Trials use varied standardized extracts; meta-analytic signals were stronger in some protocols at 600 mg/day or more. - Often later in the day or divided, depending on the study. - Often 8 weeks or longer in sleep trials.Drowsiness can occur; do not combine casually with sedating medicines.

Safety notes

  • Liver injuryRare cases of liver injury have been linked to ashwagandha. Stop use and seek medical assessment for jaundice, dark urine, persistent nausea or marked unexplained fatigue.
  • Pregnancy, breastfeeding and surgeryNCCIH advises avoiding ashwagandha during pregnancy and breastfeeding and not using it around surgery without medical guidance.
  • Thyroid or autoimmune diseaseAshwagandha is not recommended for people with thyroid or autoimmune disorders without individualized medical review.
  • Drowsiness and gastrointestinal effectsDrowsiness, stomach upset, diarrhea and vomiting can occur and may affect training, driving or work.

Interactions

  • Thyroid hormone medicinesAshwagandha may affect thyroid function; combine only with clinician monitoring when thyroid medication is used.
  • Sedatives and anti-seizure medicinesPotential additive sedation or other effects warrant clinician or pharmacist review.
  • Diabetes and blood-pressure medicinesAshwagandha may affect glucose or blood pressure; monitoring may be needed when these medicines are used.
  • ImmunosuppressantsPeople using immune-suppressing medicines should avoid unsupervised ashwagandha because of possible immune effects.

References

  1. National Center for Complementary and Integrative Health. Ashwagandha: Usefulness and Safety NCCIH. 2026.Source
  2. Cheah KL, Norhayati MN, Husniati Yaacob L, Abdul Rahman R. Effect of Ashwagandha (Withania somnifera) extract on sleep: A systematic review and meta-analysis PLOS ONE. 2021.Source
  3. Li X, Li H, Yao S, Hou Y, Chi A. Effects of Withania somnifera (Ashwagandha) Supplementation on Exercise Performance: A Systematic Review and Three-Level Meta-Analysis Nutrients. 2026.Source