Supplements

Ashwagandha

Updated · 22 sources · Editorial policy

Ashwagandha (Withania somnifera) is a shrub from the nightshade family (Solanaceae) and an herb of traditional Ayurvedic medicine (Vaidya et al., J Ethnopharmacol 2024). Most products use extracts of the root; some also contain leaf. It is marketed mainly for stress, sleep, exercise performance and testosterone.

In the US it is sold as a dietary supplement, not as an approved drug. Dozens of small randomized trials exist, several of them funded or supplied by extract manufacturers. They suggest modest effects on stress, sleep and strength, and a small rise in testosterone. At the same time, case series have linked ashwagandha to cholestatic liver injury, and in 2024 Germany’s Federal Institute for Risk Assessment (BfR) advised several groups not to take it.

This page summarizes what clinical trials, meta-analyses and regulators report. It is for education only and is not medical advice.

Property Detail
Type Herbal dietary supplement; traditional Ayurvedic herb
Plant part Mainly root; some extracts use root and leaf
Main constituents Withanolides (steroidal lactones) and alkaloids
Route Oral (capsules, tablets, powders, teas)
Doses in trials 500–675 mg/day of standardized extract in the main trials cited here; 125–600 mg/day across 23 healthy-adult trials
Half-life ≈1.7–4.4 h for individual withanolides from a standard extract; ≈1.9–9.8 h for total withanolides depending on extract type
US status Dietary supplement; FDA does not approve supplements before marketing
EU advisory BfR (Germany) advises children, pregnant or breastfeeding women and people with liver disease not to take it
WADA status Not named on the 2026 Prohibited List

What it is

Ashwagandha root has been used in Ayurveda for centuries. The compounds thought to be most active are the withanolides, a group of steroidal lactones that includes withaferin A and withanolide A, along with withanosides (sugar-bound withanolides) and alkaloids (Wankhede et al., JISSN 2015; Kim et al., Heliyon 2023).

Commercial products vary widely. The BfR notes that the plant part used and the extraction method both change which compounds are present and in what amounts. It also states that the substances and doses responsible for effects seen in studies cannot yet be clearly identified (BfR 2024).

Most trials used branded, standardized extracts. Results from one extract may not carry over to another:

Extract (as described in trials) Plant part Standardization Used in
KSM-66 Root only At least 5% withanolides Wankhede 2015; Chandrasekhar 2012
Sensoril Root and leaf (aqueous extract) — Ziegenfuss 2018
Shoden Root and leaf 35% withanolide glycosides Lopresti 2019

Pharmacokinetics

Human pharmacokinetic data are recent and limited to single-dose studies in healthy volunteers.

Study Product and dose Time to peak Half-life
Sharma et al., Drug Metab Pers Ther 2025 400 mg root extract (2.5% withanolides) 1.0–1.4 h 1.7–4.4 h (four withanolides measured separately)
Kim et al., Heliyon 2023, 2.5% extract 185 mg total withanolides 1.5 h 1.9 h (total withanolides)
Kim et al. 2023, 35%-glycoside extract 185 mg total withanolides 2.3 h 9.8 h (total withanolides)

In the Kim crossover study of 16 healthy adults, the high-glycoside extract produced about 5.6 times the peak level of the 2.5% extract at the same withanolide dose. The two extracts were not bioequivalent. One author was affiliated with the maker of the high-glycoside extract.

The practical point is that “ashwagandha” is not one product. Exposure depends heavily on how the extract is made.

Regulatory status

  • United States. Ashwagandha is sold as a dietary supplement. Under the Dietary Supplement Health and Education Act (DSHEA), FDA has no authority to approve supplements before they are marketed, and manufacturers are responsible for their safety (FDA).
  • Germany and the EU. In September 2024 the BfR advised that children, pregnant and breastfeeding women and people with acute or pre-existing liver disease should not take ashwagandha supplements. It advised caution for everyone else and said no safe intake level could be derived from current data. It listed risk reviews by authorities in Denmark (DTU), the Netherlands (RIVM), France (ANSES) and Australia (TGA) (BfR 2024).
  • Sport. Ashwagandha is not named on the WADA 2026 Prohibited List. As with any supplement, FDA does not review the product before it is sold.

What the research shows

Strength and exercise performance

Two placebo-controlled trials in men on a resistance-training program reported larger strength gains with ashwagandha:

Trial Measure Placebo Ashwagandha
Wankhede 2015: 57 men, 600 mg/day KSM-66, 8 weeks Bench press 1RM gain +26.4 kg +46.0 kg
Wankhede 2015 Leg extension 1RM gain +9.8 kg +14.5 kg
Wankhede 2015 Arm muscle size gain +5.3 cm² +8.6 cm²
Wankhede 2015 Drop in body fat percentage 1.5% 3.5%
Ziegenfuss 2018: 38 men, 500 mg/day Sensoril, 12 weeks Squat 1RM gain +10.0 kg +19.1 kg
Ziegenfuss 2018 Bench press 1RM gain +8.0 kg +12.8 kg

Sources: Wankhede et al., JISSN 2015; Ziegenfuss et al., Nutrients 2018.

In the Ziegenfuss trial, there were no other between-group differences in body composition apart from a small change in fat distribution. Both trials were small, and in the Wankhede trial the extract was supplied by its manufacturer.

Pooled analyses are more cautious:

  • A 2026 meta-analysis of resistance-training trials could pool only 3 RCTs (n = 161). Ashwagandha was linked to larger gains in bench press (SMD 0.60, 95% CI 0.20–1.01) and lower-body 1RM (SMD 0.52, 95% CI 0.19–0.86), with no effect on body fat. Under a stricter statistical method, both strength results lost significance, each depended on one influential trial, and certainty was rated low (Lee and Heo, Nutrients 2026).
  • A 2026 meta-analysis of 13 trials (599 participants) found an average improvement in exercise performance (Hedges’ g 0.47, 95% CI 0.25–0.69). The 95% prediction interval (−0.40 to 1.33) crossed zero, so a new trial could plausibly show no benefit. The effect was most consistent for aerobic endurance; strength effects were positive but uncertain (Li et al., Nutrients 2026).

SMD (standardized mean difference) expresses an effect in standard-deviation units, so trials that used different scales can be pooled.

Testosterone

Study Population Dose and duration Result vs placebo
Wankhede 2015 Men aged 18–50 new to resistance training 600 mg/day, 8 weeks Serum testosterone +96 ng/dL vs +18 ng/dL (p = 0.004)
Lopresti 2019 57 overweight men aged 40–70 with mild fatigue (crossover) 21 mg withanolide glycosides/day, 8 weeks Salivary testosterone 14.7% higher; DHEA-S 18% higher
Fornalik 2026 meta-analysis 23 RCTs, 1,706 participants Various Men: +57.4 ng/dL mean difference; no increase in women

The effects are small relative to normal male levels. In the Wankhede trial, baseline testosterone was about 630–675 ng/dL, and post-treatment levels (727 vs 693 ng/dL) did not differ significantly between groups. In the Lopresti trial, which the extract maker funded, fatigue, vigor and sexual well-being did not improve more than with placebo.

Ashwagandha is not a substitute for testosterone therapy. The rise seen in trials is a fraction of what prescribed testosterone produces (see testosterone cypionate).

Male fertility

A pilot trial randomized 46 men with low sperm counts to 675 mg/day of root extract or placebo for 90 days (Ambiye et al., 2013). In the ashwagandha group, compared with baseline:

  • sperm concentration rose 167% (9.6 to 25.6 million/mL);
  • semen volume rose 53%;
  • sperm motility rose 57%.

Placebo changes were described as minimal. These are within-group changes from a single small study, and pregnancy rates were not the outcome.

Stress, anxiety and cortisol

In a trial of 64 adults with chronic stress, 300 mg of KSM-66 twice daily for 60 days lowered serum cortisol by 27.9% from baseline, compared with 7.9% on placebo (Chandrasekhar et al., 2012). Perceived Stress Scale scores fell 44.0% vs 5.5%.

A 2022 meta-analysis of 12 trials (1,002 participants) found large average reductions (Akhgarjand et al., Phytother Res 2022):

Outcome SMD vs placebo (95% CI) Heterogeneity (I²)
Anxiety −1.55 (−2.37 to −0.74) 93.8%
Stress −1.75 (−2.29 to −1.22) 83.1%

The very high heterogeneity means trial results varied widely, and the authors rated the certainty of evidence as low. The 2026 hormone meta-analysis also found lower cortisol with ashwagandha (SMD −1.18) (Fornalik et al., 2026).

Sleep

A meta-analysis of 5 RCTs (400 participants) found a small but significant improvement in overall sleep (SMD −0.59, 95% CI −0.75 to −0.42) (Cheah et al., PLoS One 2021). Effects were larger in people with diagnosed insomnia, at doses of at least 600 mg/day, and with treatment of at least 8 weeks. The authors noted that data on serious adverse effects were limited.

Thyroid

In a trial of 50 adults with subclinical hypothyroidism (TSH 4.5–10 μIU/L), 600 mg/day of root extract for 8 weeks improved TSH, T3 and T4 compared with placebo (Sharma et al., 2018). The 2026 meta-analysis found no effect on TSH or T3 overall, but a modest rise in T4 (+0.61 µg/dL) (Fornalik et al., 2026). The ability to raise thyroid hormone is relevant to safety, discussed below.

Side effects and risks

Tolerability in trials

A 2026 systematic review of 23 randomized trials of standardized root extracts in healthy adults (2,317 participants; 125–600 mg/day for up to 180 days) reported no serious adverse events attributed to ashwagandha (Coope et al., 2026). Liver, kidney, blood and hormone markers stayed within normal ranges. Mild effects such as stomach upset, headache and drowsiness were infrequent and occurred in both groups.

The BfR points out that most trials were designed to show benefit and did not record adverse effects systematically. Reported effects include nausea, vomiting, diarrhea, drowsiness, headache, dizziness and skin rash (BfR 2024). Long-term data beyond about 6 months are lacking.

Liver injury

Liver injury has been documented in case reports and case series, and the BfR cites these reports as a particular reason for caution:

  • Iceland and the US DILIN registry. Five cases, with jaundice after 2–12 weeks of use (Björnsson et al., Liver Int 2020). The injury was cholestatic or mixed, meaning bile flow was impaired. Itching and high bilirubin lasted 5–20 weeks. No patient developed liver failure, and liver tests normalized within 1–5 months in the four patients followed up. Lab analysis confirmed ashwagandha in the products and found no other toxins.
  • India. Of 23 patients with ashwagandha-linked liver injury at several centers, 8 had used single-ingredient products (Philips et al., Hepatol Commun 2023). Five of the 8 had pre-existing chronic liver disease. Three presented with acute-on-chronic liver failure, and all three died. Chemical analysis found no adulterants.
  • Scoping review. A 2026 review of 13 publications (25 patients) found mostly cholestatic injury with jaundice and itching, usually resolving over weeks to months after stopping (McIntyre et al., Cureus 2026). Severe outcomes included one liver transplant and three deaths in patients with cirrhosis.

The review describes the injury as idiosyncratic, meaning it is an unpredictable reaction in individual users. Because the analyzed products were not adulterated, the plant itself is the suspected cause.

Thyroid overactivity

Because ashwagandha can raise thyroid hormone levels, there are case reports of thyrotoxicosis (excess thyroid hormone). One 73-year-old woman developed a fast heart rhythm (supraventricular tachycardia) and suppressed TSH after two years of self-treating hypothyroidism with ashwagandha. She recovered fully after stopping (Kamal et al., Cureus 2022).

Interactions

The BfR lists possible interactions with drugs that lower blood glucose (antidiabetics), lower blood pressure (antihypertensives) or suppress the immune system (immunosuppressants). It advises seeking medical advice before combining ashwagandha with such medicines (BfR 2024). Given the thyroid effects above, people taking thyroid medication have added reason for caution.

Who should not use it

Based on the BfR advice and the case literature, the following groups are advised to avoid ashwagandha:

  • pregnant women (it has historically been used to induce abortion) and breastfeeding women;
  • children;
  • people with acute or pre-existing liver disease; the scoping review specifically advises people with advanced chronic liver disease to avoid it.

Thyroid disease is a further reason for caution, given the trial and case-report evidence above.

Key takeaways

  • A supplement, not a drug. Ashwagandha is an Ayurvedic root extract sold in the US as a dietary supplement, without FDA review of safety or efficacy before sale.
  • Products differ a lot. Root vs leaf, extraction method and withanolide content change how much reaches the blood; measured half-lives range from about 2 to 10 hours.
  • Modest, uncertain performance effects. Small trials show larger strength gains with training, but meta-analyses rate the evidence low-certainty and find no reliable effect on body fat.
  • Small testosterone rise. Pooled data show about +57 ng/dL in men, far below what testosterone therapy produces, and some key trials were manufacturer-funded.
  • Best evidence is for stress and sleep. Meta-analyses show reductions in anxiety, stress and cortisol and a small sleep benefit, with high variability between trials.
  • Documented, serious liver injury. Case series describe cholestatic hepatitis, with deaths in people who already had liver disease; German regulators advise several groups to avoid it.

Sources

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  2. Ziegenfuss TN, Kedia AW, Sandrock JE, et al. Effects of an aqueous extract of Withania somnifera on strength training adaptations and recovery: the STAR trial. Nutrients. 2018;10(11):1807. PubMed.
  3. Lee JC, Heo AS. Adjunctive ashwagandha (Withania somnifera) supplementation and resistance-training adaptations in healthy adults: a systematic review and random-effects meta-analysis of muscular strength, chest circumference, and body composition. Nutrients. 2026;18(17):2815. PubMed.
  4. Li X, Li H, Yao S, et al. Effects of Withania somnifera (ashwagandha) supplementation on exercise performance: a systematic review and three-level meta-analysis. Nutrients. 2026;18(12):1915. PubMed.
  5. Lopresti AL, Drummond PD, Smith SJ. A randomized, double-blind, placebo-controlled, crossover study examining the hormonal and vitality effects of ashwagandha (Withania somnifera) in aging, overweight males. Am J Mens Health. 2019;13(2):1557988319835985. PubMed.
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  7. Ambiye VR, Langade D, Dongre S, et al. Clinical evaluation of the spermatogenic activity of the root extract of ashwagandha (Withania somnifera) in oligospermic males: a pilot study. Evid Based Complement Alternat Med. 2013;2013:571420. PubMed.
  8. Chandrasekhar K, Kapoor J, Anishetty S. A prospective, randomized double-blind, placebo-controlled study of safety and efficacy of a high-concentration full-spectrum extract of ashwagandha root in reducing stress and anxiety in adults. Indian J Psychol Med. 2012;34(3):255–262. PubMed.
  9. Akhgarjand C, Asoudeh F, Bagheri A, et al. Does ashwagandha supplementation have a beneficial effect on the management of anxiety and stress? A systematic review and meta-analysis of randomized controlled trials. Phytother Res. 2022;36(11):4115–4124. PubMed.
  10. 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;16(9):e0257843. PubMed.
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  15. Coope OC, Willems MET, Levington A, et al. Back to the roots: safety and tolerability of standardised ashwagandha (Withania somnifera) root extract in healthy adults: a systematic review of biomarkers and adverse events. Pharmaceuticals (Basel). 2026;19(5):725. PubMed.
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  22. World Anti-Doping Agency. World Anti-Doping Code International Standard: Prohibited List 2026. WADA 2026 Prohibited List.