Does ashwagandha work for stress? The trials say maybe, the safety data say be careful

Ashwagandha, an Ayurvedic herb now sold across the wellness aisle for stress, sleep and "cortisol balance," does appear to lower self-reported stress and anxiety when tested against placebo in randomised trials — but the evidence is rated low-certainty, the trials are small and strikingly inconsistent with one another, and the most recent pooled estimates are so large they are hard to believe [s1][s2]. A separate body of work flags safety signals the marketing rarely mentions, including liver injury and thyroid disruption [s3]. In short: the herb is plausibly active, the headline effect sizes are not trustworthy, and "natural" is not the same as risk-free.

This article describes published research. It is not advice about whether to take a supplement, and anyone taking prescribed medication or with thyroid or liver conditions should raise that question with a clinician rather than an article.

What the trials show

A systematic review and dose-response meta-analysis in Phytotherapy Research pooled randomised controlled trials of ashwagandha extract against placebo for anxiety and stress, searching databases through December 2021 [s1]. Twelve eligible trials with 1,002 participants, aged between 25 and 48, were included [s1].

Ashwagandha significantly reduced anxiety (standardised mean difference −1.55, 95% CI −2.37 to −0.74) and stress (SMD −1.75, 95% CI −2.29 to −1.22) compared with placebo [s1]. Those are large effects on paper. The number to read alongside them is the heterogeneity: I² was 93.8% for anxiety and 83.1% for stress [s1]. Heterogeneity that high means the individual trials disagree with each other so much that a single pooled figure is close to meaningless — the studies are not really measuring one stable effect.

The authors were explicit about this. They rated the certainty of the evidence low for both outcomes, and their dose-response analysis pointed to a favourable effect on anxiety up to 12,000 mg/day and on stress at 300 to 600 mg/day [s1] — a range so wide it underlines how unsettled the dosing question remains.

Why the newest numbers should raise an eyebrow

A 2026 dose-response meta-analysis in Complementary Therapies in Medicine pooled 22 randomised trials and reported even larger effects: stress SMD −5.88 (95% CI −8.15 to −3.60), anxiety SMD −6.87 (95% CI −8.77 to −4.97) and depression SMD −5.68 (95% CI −8.43 to −2.94) [s2]. It also found a significant relationship between dose and stress reduction, both linear (coefficient 0.005, p = 0.031) and non-linear (p = 0.005) [s2].

An effect of that size is the tell, not the triumph. A standardised mean difference near −6 or −7 implies the average treated participant scored roughly six to seven standard deviations better than placebo on a symptom scale — a magnitude that does not occur for any established anxiety treatment and is far more consistent with small studies, measurement inconsistency and selective reporting than with a genuinely enormous drug effect. The authors' own conclusion is cautious: the evidence is "promising" but requires well-designed, high-quality trials to resolve the heterogeneity and establish effective doses [s2]. The two reviews together describe a literature that leans positive and is too weak to bank.

The safety side the labels skip

Ashwagandha is regulated as a food supplement in most markets, which means it reaches shelves without the safety review a drug would face — and the safety literature is not empty. A 2026 critical review in Phytotherapy Research catalogued reported harms from the herb's bioactive compounds, including gastrointestinal effects, immune hypersensitivity, liver toxicity and endocrine disruption, particularly with prolonged or high-dose use [s3].

The mechanisms are specific rather than hand-waving. The review describes metabolism of ashwagandha compounds through cytochrome P450 enzymes into reactive intermediates capable of causing oxidative stress and hepatotoxicity, and links its endocrine activity to thyrotoxicosis and adrenal suppression [s3]. Because it is metabolised through the same enzyme pathways as many medicines, the review flags the potential for interactions with prescribed drugs [s3]. Its overall call is for standardised dosing, better pharmacovigilance, long-term safety studies and revised regulatory guidance [s3] — not the profile of an ingredient whose safety is settled.

That matters most for the people the product is marketed to: someone adding a "calm" supplement on top of an antidepressant, a thyroid medication, or a sedative is exactly the scenario where an unlabelled interaction or an idiosyncratic liver reaction would surface.

Reading it together

The honest summary is that ashwagandha is probably not inert — multiple randomised trials point the same direction on stress and anxiety — but the quality of that evidence is low, the pooled effect sizes are inflated by wild inter-study disagreement, and the safety data are thin precisely where a consumer would want them to be thick [s1][s2][s3]. This is the same pattern seen across much of the supplement shelf, where real trials exist but are short, small and rarely independent. Ashwagandha sits alongside magnesium, melatonin and the multivitamin as products sold with more confidence than the trials support, and the case for non-pharmacological stress tools such as structured breathing or mindfulness apps rests on evidence that is, at minimum, no weaker.

What to watch

The thing that would settle the efficacy question is what both reviews say is missing: large, pre-registered, independently funded trials with standardised extracts and doses, and enough of them to pull the heterogeneity down [s1][s2]. On safety, the useful signal will be systematic pharmacovigilance and long-term data rather than the scattered case reports the field currently relies on [s3]. Until then, the gap between the marketing and the evidence is the story.

Sources

• Does Ashwagandha supplementation have a beneficial effect on the management of anxiety and stress? A systematic review and meta-analysis of randomized controlled trials — Phytotherapy Research, 2022-08-25
• Effects of ashwagandha (Withania somnifera) on mental health in adults: a systematic review and dose-response meta-analysis of randomized controlled trials — Complementary Therapies in Medicine, 2026-02-03
• Potential Adverse Effects of Ashwagandha: A Critical Review of Preclinical and Clinical Evidence — Phytotherapy Research, 2026-01-08