Ashwagandha is one of the most-studied adaptogens on the market — and also one of the most overhyped. Here's what the actual clinical trials show about stress, cortisol, and sleep, plus the safety details worth knowing before you start.

Written by Vita Globe Editorial Team | Reviewed against peer-reviewed research and NIH guidance

What Ashwagandha Actually Does

Ashwagandha is a root extract from Withania somnifera, a shrub used for centuries in Ayurvedic practice, and it's classified today as an "adaptogen" — a substance thought to help the body regulate its stress response rather than target one specific symptom. Most of the modern research focuses on standardized root extracts (commonly branded as KSM-66 or Sensoril), which concentrate the plant's withanolide compounds to consistent, testable doses — a meaningfully different thing than raw ashwagandha powder, where potency varies widely. That distinction matters because nearly all of the clinical evidence below comes from these standardized extracts, not from ashwagandha in general.

Stress and Cortisol: What the Research Shows

The strongest, most recent evidence comes from a 2025 systematic review and meta-analysis in BJPsych Open pooling 15 randomized controlled trials and 873 participants. It found ashwagandha significantly reduced anxiety scores (on the Hamilton Anxiety Rating Scale), perceived stress (on the Perceived Stress Scale), and serum cortisol compared with placebo, concluding the herb is "safe and effective in reducing stress and anxiety in adult patients"^[1]. Notably, that same analysis found no significant improvement in overall quality-of-life scores — a useful reminder that "less stressed on a questionnaire" and "life feels better" aren't automatically the same thing^[1].

Worth being honest about: a separate 2025 meta-analysis reached a more mixed conclusion. Pooling seven studies on cortisol and six on perceived stress (488 participants total), it found a statistically significant drop in cortisol — but no significant effect on how stressed people actually felt^[2]. The two reviews don't fully agree, and that's the honest state of the science right now: ashwagandha reliably moves a biological stress marker, and most (not all) of the trial evidence also points to people feeling less stressed and anxious — but the effect on perceived stress specifically is less consistent across analyses than the cortisol effect is.

Sleep Benefits

Separate from the stress research, a 2021 meta-analysis of five sleep-focused studies (372 participants), cited by the NIH Office of Dietary Supplements, found ashwagandha had "a small but significant effect on improving sleep compared with placebo." The benefit was more pronounced at doses around 600 mg/day taken for eight or more weeks, and particularly for people who already had insomnia rather than good sleepers looking for an extra edge^[3].

How to Take It

Across the clinical trials the NIH fact sheet reviewed, doses ranged widely — from 240 mg to 1,250 mg per day of standardized extract, up to 12,000 mg/day of whole root granules in some studies. The doses most consistently linked to benefit were 500–600 mg/day of standardized extract for stress and anxiety, and 600 mg/day for sleep, generally taken for 8 weeks or longer before judging whether it's working^[3]. Unlike creatine or caffeine, ashwagandha isn't an acute, same-day supplement — the research reflects consistent daily use over weeks, not an as-needed dose on a stressful day.

Safety: Thyroid, Liver, and Pregnancy

Ashwagandha is generally well tolerated at studied doses, but it isn't risk-free, and the honest picture has gotten more detailed in recent years as case reports have accumulated.

Thyroid: Ashwagandha may increase thyroid hormone (T4) levels, and case reports of thyrotoxicosis (an overactive thyroid state) have been documented. Anyone with a thyroid condition, or taking thyroid medication, should talk to a doctor before starting it^[3].

Liver: NIH's LiverTox database has documented roughly 23 reported cases of clinically apparent liver injury linked to ashwagandha, typically presenting as jaundice and itching 2 to 12 weeks after starting the supplement (though onset ranged from as early as 3 days to as late as a year). The dose in these cases varied widely — some at typical supplement doses (150–600 mg/day), others much higher — and the relationship between dose and risk isn't well understood. The reassuring part: most cases resolved within 1 to 4 months of stopping the supplement, though rare, severe cases requiring liver transplantation have occurred, generally in people with pre-existing liver disease^[4].

Pregnancy: Experts generally advise against use during pregnancy due to a potential association with spontaneous abortion, though this is disputed by some herbal-medicine authorities and the evidence isn't fully settled either way. Given the uncertainty, it's not a supplement to start during pregnancy without a doctor's input^[3].

Medication interactions: Ashwagandha may interact with thyroid medications, diabetes medications, blood pressure medications, immunosuppressants, and sedatives — worth flagging to a doctor or pharmacist if you take any of these regularly^[3].

Stress and sleep feed each other — for the biology of how cortisol disrupts sleep and which other relaxation approaches have real evidence behind them, see our guide to how stress impacts sleep.

Frequently Asked Questions

How long does ashwagandha take to work?

Most of the positive trial results come from consistent daily use over 8 weeks or longer, not a single dose. It's not designed to work like an as-needed anti-anxiety aid on a stressful day^[3].

Is ashwagandha safe if I have a thyroid condition?

Talk to a doctor first. Ashwagandha can raise thyroid hormone levels, and case reports of thyrotoxicosis exist, so it needs medical oversight if you have a thyroid condition or take thyroid medication^[3].

Can ashwagandha hurt my liver?

Liver injury is rare but real — NIH's LiverTox database has documented about 23 cases, most reversible after stopping the supplement. If you develop jaundice, dark urine, or persistent itching while taking it, stop and see a doctor^[4].

Is ashwagandha safe during pregnancy?

Most experts advise against it due to a possible association with spontaneous abortion, though this is disputed by some herbal authorities. Given the uncertainty, check with your doctor before use during pregnancy^[3].

Does ashwagandha definitely lower stress, or just cortisol?

Both, according to most of the evidence — but not every analysis agrees. A large 2025 meta-analysis found reductions in both cortisol and perceived stress^[1], while a separate 2025 review found cortisol dropped without a significant change in how stressed people felt^[2]. The cortisol effect is the more consistent finding across the research.

These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease. The content in this article is for informational purposes only and is not a substitute for professional medical advice.