Ashwagandha

The single stress, sleep and strength trials cited below lasted six weeks to 60 days [5][8][11]. Our evidence grading method explains what each grade requires.

Does ashwagandha lower stress?

Trials point that way, but the evidence is mixed. A 2022 meta-analysis (a study that pools trial results) of 12 randomized controlled trials with 1,002 adults aged 25 to 48 found lower stress levels with ashwagandha than with placebo (SMD -1.75; 95% CI -2.29 to -1.22) [1]. Heterogeneity, the spread between trial results, was high (I2 = 83.1%), and the authors rated the certainty of the evidence low [1]. A 2024 meta-analysis of nine trials in 558 patients with stress or anxiety found lower Perceived Stress Scale scores (mean difference -4.72 points) and lower serum cortisol than placebo [2].

Not every pooled analysis agrees. A 2025 meta-analysis limited to trials of at least two weeks found that cortisol fell (-1.16 µg/dL) but found no significant effect on perceived stress across six trials (SMD -0.355; 95% CI -1.188 to 0.47) [3]. A 2026 dose-response meta-analysis of 22 trials reported a significant association between dose and stress scores, and also called for better trials to address heterogeneity [4].

The individual trials behind these analyses are small and often industry-linked. In 64 adults with a history of chronic stress, 300 mg of a root extract twice a day for 60 days reduced scores on all stress scales compared with placebo, and serum cortisol fell [5]; the extract, KSM-66, was provided by its manufacturer, Ixoreal Biomed [5]. In 60 stressed but healthy adults, 240 mg of a standardized extract once daily for 60 days reduced scores on the Hamilton Anxiety Rating Scale compared with placebo, while the reduction on the Depression, Anxiety and Stress Scale was not statistically significant (P = .096); this trial was funded by the extract maker, Arjuna Natural Ltd [6].

Does ashwagandha improve sleep?

There is a small effect in trials. A 2021 meta-analysis of five randomized controlled trials with 400 participants found a small but significant effect on overall sleep compared with placebo (SMD -0.59; 95% CI -0.75 to -0.42; I2 = 62%) [7]. The effect was more prominent in three subgroups: adults diagnosed with insomnia (a clinical population), doses of 600 mg/day or more, and durations of at least 8 weeks [7]; the insomnia result may not apply to healthy adults. All five trials were conducted in India, and one declared partial sponsorship by the manufacturer [7].

One trial enrolled 150 healthy adults with non-restorative sleep, meaning sleep that does not feel refreshing [8]. After 120 mg of a standardized extract once daily for six weeks, self-reported sleep quality rose 72% in the ashwagandha group against 29% with placebo, and actigraphy (a wrist-worn activity monitor) showed better sleep efficiency, total sleep time and sleep latency [8]. Crossref lists the extract maker, Arjuna Natural, as the funder of that trial [8]. In a smaller eight-week trial of 40 healthy adults and 40 adults with insomnia, a clinical population, improvements were larger in the insomnia group than in the healthy group [9].

Does ashwagandha increase strength with training?

Possibly, but the evidence is fragile. A 2026 meta-analysis of resistance-training trials pooled three trials with 161 healthy adults and found greater gains than placebo in bench-press one-repetition maximum (1-RM, the most weight lifted once; SMD 0.60) and lower-body 1-RM (SMD 0.52) [10]. Under a stricter statistical adjustment both strength estimates lost significance, each depended on one influential trial, and certainty was rated low [10]. The reviewers concluded that current evidence does not establish a meaningful benefit for resistance-training adaptations; all three trials were funded or supplied by ashwagandha manufacturers [10].

One trial randomized 57 young men with little resistance-training experience to 300 mg of root extract twice daily or placebo for 8 weeks [11]. Bench-press strength rose 46.0 kg with ashwagandha against 26.4 kg with placebo [11]. That trial tested KSM-66, made by Ixoreal BioMed [11]. A broader 2026 meta-analysis of 20 trials found improved muscle strength (SMD = 0.58), significant in physically active people but not in untrained or special populations [12].

Does ashwagandha improve endurance?

Trials suggest a modest benefit, mostly in young adults and athletes. A 2026 meta-analysis of 13 randomized controlled trials with 599 participants found better overall exercise performance with ashwagandha than placebo (Hedges' g = 0.47), but the prediction interval crossed zero, meaning some future trials could find no benefit [13]. Evidence was most consistent for aerobic endurance (g = 0.54), while strength effects were positive but uncertain and power data were sparse [13]. An earlier meta-analysis of four trials (142 participants) found higher VO2max, the maximum rate of oxygen use during exercise, by a mean difference of 3.00 with high heterogeneity [14].

Does ashwagandha improve memory?

The evidence is limited and comes partly from clinical groups. A 2026 meta-analysis of 20 trials with 1,249 participants reported improved memory (SMD = 0.52) and attention and processing speed (SMD = 0.29) compared with placebo [12]. Its trials mixed healthy, physically active and special populations [12]. An earlier systematic review of five clinical studies drew on older adults with mild cognitive impairment and adults with schizophrenia, schizoaffective disorder or bipolar disorder, all clinical populations [15]; results from these groups may not apply to healthy adults. NCCIH states there is not enough evidence to determine whether ashwagandha helps cognitive function [27].

What the evidence does not show

A 2026 meta-analysis found no significant effects on body weight or body fat percentage [12], and the resistance-training meta-analysis found no significant effect on body fat [10]. In 57 overweight men aged 40 to 70 with mild fatigue, an extract delivering 21 mg of withanolide glycosides a day raised testosterone 14.7% more than placebo, but there were no significant between-group differences in fatigue, vigor or sexual well-being; Crossref lists Arjuna Natural Ltd, the extract maker, as the funder [16].

Trials gave extracts once daily [6][8] or twice daily [5][11], for six weeks to 60 days. KSM-66 is a root extract [5] made with a water-based process [11].

The authors of a 2023 study wrote that human pharmacokinetics, meaning how the body absorbs and clears withanolides, had not been fully evaluated [25]. In their single-dose crossover study of 16 healthy volunteers, the half-life of total withanolides (the time for blood levels to fall by half) was 5.18 times longer with a withanolide glycoside-rich extract than with a standard 2.5% extract [25]. One author, affiliated with the extract maker Arjuna Natural, declared a pending patent with the company [25].

NCCIH says ashwagandha may be safe in the short term, up to 3 months, and that there is not enough information to judge long-term safety [27][40]. It reports that ashwagandha preparations may cause drowsiness, stomach upset, diarrhea and vomiting [27]. In trials, adverse effects were mostly mild: four of nine trials in one meta-analysis reported mild to moderate adverse events [2], and in a 60-day trial they were comparable to placebo (that trial used an extract supplied by its manufacturer) [5]. In an eight-week placebo-controlled trial of 80 healthy adults, 40 of whom took 300 mg twice daily, blood, liver and thyroid measures showed no statistically significant changes [21].

Liver injury is the main safety signal. LiverTox, the NIH liver-toxicity reference, reports that ashwagandha has not been linked to liver enzyme rises during use but has been implicated in cases of clinically apparent liver injury [28]. In a case series from Iceland and the US, all five people developed jaundice, with symptoms such as nausea, tiredness, itching and abdominal discomfort, 2-12 weeks after starting ashwagandha-containing supplements; none developed liver failure, and liver tests returned to normal within 1-5 months in four [17]. A case series from India described 8 people with injury from single-ingredient products; of 5 with underlying chronic liver disease, 3 developed acute-on-chronic liver failure and all 3 died [18]. Chemical analysis in that series found no adulteration or contamination [18]. A 2026 scoping review of 13 publications covering 25 patients found most recovered after stopping, while one person needed a liver transplant and three people with pre-existing cirrhosis died [19].

Regulators have reported similar signals. Australia's TGA had received 12 reports of liver problems up to February 5, 2024, 7 with enough information to suggest liver injury that may have been caused by Withania somnifera [34]. It also reported sudden gastrointestinal reactions, 16 of them severe enough for hospital admission [34]. The TGA lists warning signs including yellowing of the skin or eyes, dark urine, nausea, vomiting, unusual tiredness and abdominal pain, and advises stopping and seeking medical advice if they appear [34]. Health Canada's 2026 review did not find sufficient evidence to establish a definite link with liver injury, but could not rule one out and will keep monitoring [33]. As a mechanism, one review proposes that cytochrome P450 enzymes can convert its constituents into reactive intermediates [20].

Thyroid effects have also been reported. A 73-year-old woman developed thyrotoxicosis with a fast heart rhythm after two years of use, which resolved after stopping [23], and LiverTox summarizes a similar case in a previously healthy 32-year-old [28]. In a pilot trial in 50 adults with subclinical hypothyroidism, a clinical population, 600 mg daily for 8 weeks changed TSH, T3 and T4 levels compared with placebo [22]. The NIH Office of Dietary Supplements fact sheet, as archived on November 2, 2026, notes three case reports of thyrotoxicosis in women taking ashwagandha extract [40], and a 2026 review links its endocrine activity to thyrotoxicosis and adrenal suppression [20].

NCCIH reports evidence that ashwagandha might interact with medicines for diabetes and high blood pressure, immunosuppressants, sedatives, anti-seizure medicines and thyroid hormone medicines [27]. A 2026 review of adverse effects also identifies groups that may be at increased risk of adverse reactions and interactions with prescribed drugs [20]. Health Canada requires products under its monograph to carry a caution about drowsiness when driving or using machinery [32]. As of November 11, 2026, a PubMed search found no primary human drug-interaction trials of ashwagandha.

These sources describe what has been reported, not what is right for any individual. If you take any of these medicines, talk to your doctor or pharmacist before combining them with ashwagandha.