Ashwagandha and Cortisol: What the Research Actually Shows

Cortisol is the most measured outcome in the whole of ashwagandha research. Almost every trial takes a blood or saliva sample, and almost every write-up leads with the number. It has become the headline claim of an entire supplement category.

Which makes it worth looking at properly. The research is more interesting than the headlines, partly because of what it found and partly because of where the studies disagree with each other.

First, What Cortisol Actually Is

Cortisol has picked up a reputation as a villain, and that reputation is not quite fair. It is a hormone produced by the adrenal glands, and it is doing something useful almost all of the time. It helps regulate blood sugar, blood pressure, the immune response and the sleep-wake cycle.

It also follows a daily rhythm. Levels rise sharply in the half hour after you wake, which is part of how you get going in the morning, then decline across the day to a low point overnight. Low cortisol is not a goal. A well-shaped curve is.

This matters when reading the research, because the trials below are measuring cortisol in people who reported being under sustained stress. That is a specific context, and it is not the same as saying lower is universally better.

The Trial Everyone Quotes

Nearly every article on this subject traces back to a single study: Chandrasekhar and colleagues, published in the Indian Journal of Psychological Medicine in 2012.

Sixty-four adults with a history of chronic stress were randomised to receive either 300mg of a high-concentration full-spectrum ashwagandha root extract twice daily, or a placebo, for 60 days. Neither the participants nor the researchers knew who was getting which.

The results were striking. Serum cortisol fell by 27.9 per cent in the ashwagandha group, against 7.9 per cent in the placebo group, a difference reported at p=0.0006. Scores on the Perceived Stress Scale fell by 44 per cent, against 5.5 per cent on placebo.

That is a large effect, and it is why the study gets quoted so relentlessly. It is also worth being clear about its limits. It was a single centre, 64 people, one country, one branded extract, and two months. A promising result, not a settled one.

A single striking trial is a starting point for a question, not an answer to it. What matters is whether the effect survives being repeated by other people, in other places, with other preparations.

Does It Hold Up Across More Studies?

Broadly, on cortisol, yes.

A 2021 systematic review identified seven randomised trials covering 491 adults, all conducted in India, who took ashwagandha or placebo for six to eight weeks at doses ranging from 240mg to 1,250mg of extract per day. Pooled together, the studies found significant reductions in stress and anxiety on validated rating scales, along with reductions in serum cortisol compared with placebo. Notably, the benefits appeared greater at 500mg to 600mg per day than at lower doses.

A 2025 systematic review and meta-analysis published in BJPsych Open went further, pooling 15 randomised controlled trials with a combined 873 participants. It reported statistically significant reductions in cortisol, in Perceived Stress Scale scores and on the Hamilton Anxiety Scale.

So the direction of travel is fairly consistent. Across multiple trials and multiple preparations, ashwagandha is associated with lower measured cortisol than placebo.

Where the Picture Gets Complicated

Here is the part that rarely makes it into a marketing bullet point.

A separate systematic review and meta-analysis, published in Nutrition and Health in August 2025, looked at seven cortisol studies and six perceived stress studies covering 488 participants. Its finding is right there in the title: significant cortisol reduction, but no significant effect on perceived stress.

The biomarker moved. The feeling, in that pooled analysis, did not.

It is not an isolated result. A 2023 randomised trial of 120 adults who were overweight and experiencing low energy, published in the Journal of Psychopharmacology, ran for 12 weeks using a standardised root extract. Compared with placebo, it did not reduce perceived stress. It did reduce fatigue.

Two reasonable readings of this exist, and the honest position is that we do not yet know which is right. One is that cortisol is an imperfect proxy for how stressed a person feels, which is true of a lot of biomarkers. The other is that the perceived stress trials are small, short, and measuring something notoriously noisy, so the effect may be real but harder to detect. The reviews themselves call for longer trials in broader populations, which is what you would expect them to say if the question were genuinely open.

Dose and Duration Are Not Details

If there is one practical thread running through all of this, it is that the trials which found effects were not short and were not low dose.

Most ran for six to eight weeks or longer. The doses that performed best clustered around 300mg to 600mg per day of a standardised extract. In 2022, a taskforce convened by the World Federation of Societies of Biological Psychiatry and the Canadian Network for Mood and Anxiety Treatments issued a provisional recommendation of 300mg to 600mg per day of root extract standardised to 5 per cent withanolides for generalised anxiety disorder, while explicitly noting that more data is needed before that recommendation could be made stronger.

Nothing in this literature works on day three. Anyone telling you otherwise is not describing the research.

The Thing Almost Nobody Mentions

Read the trials closely and a genuine problem appears. They are not all testing the same thing.

The studies above used a range of different branded, standardised extracts, each with its own extraction method, its own withanolide content, and its own plant material. Some use root only. Some use root and leaf, and the chemistry of root and leaf differs. Doses in the literature span 240mg to 1,250mg of extract per day, plus one study using 12,000mg of whole root granules.

The NIH Office of Dietary Supplements puts it plainly in its health professional fact sheet: because studies have used various preparations with different extraction and standardisation processes, it is difficult to identify specific extracts or recommended amounts.

The practical consequence is that a result obtained with one standardised extract at one dose does not automatically transfer to a different preparation at a different dose. Withanolide content is the number that actually matters, and it is the number most often left off a label.

Safety, and Who Should Not Take It

This section is not a formality, and it belongs in any honest write-up of this ingredient.

Ashwagandha appears to be well tolerated in trials for up to about three months. Common side effects reported are mild, and include stomach upset, loose stools, nausea and drowsiness. Evidence on safety over months or years is lacking.

There are also documented reports of more serious effects. Case reports have linked ashwagandha use to acute liver injury, including a case series from Iceland and the US Drug-Induced Liver Injury Network. Some research suggests it may affect thyroid function, and thyrotoxicosis has been described in case reports. It may interact with thyroid, diabetes, blood pressure, immunosuppressant and sedative medications.

Some experts advise against use during pregnancy, and the French agency ANSES issued a statement in 2024 recommending against use in certain groups including pregnant and breastfeeding women and people with endocrine disorders. Denmark banned its use in food supplements in 2023.

In the United Kingdom, the Food Standards Agency has referred ashwagandha to the Committee on Toxicity for a formal risk assessment. A call for evidence closed on 25 June 2026 and the Committee's work is ongoing. As of August 2026 the outcome has not been published. Ashwagandha is not banned in the UK and remains legally available, but anyone taking it should know that a review is underway.

If you are pregnant or breastfeeding, under 18, have a thyroid or liver condition, or take any prescribed medication, this is a conversation to have with your doctor or pharmacist rather than a decision to make from a blog post.

The Honest Summary

Ashwagandha has a real evidence base, which is more than can be said for a lot of what gets sold alongside it. The cortisol finding has been repeated often enough, by enough independent groups, to be taken seriously.

What it does not have is certainty. The trials are mostly small, mostly short, mostly from one country, and mostly conducted on branded extracts that differ from one another in ways that are likely to matter. The relationship between the cortisol number and how a person actually feels is unresolved. The long-term safety picture is genuinely incomplete, and a UK regulator is currently examining it.

All of that can be true at once. It usually is, with botanicals. The useful skill is holding the promising evidence and the open questions in mind at the same time, rather than picking whichever one suits the story you wanted to tell.

References

1. Chandrasekhar, K., Kapoor, J. and 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 Journal of Psychological Medicine, 34(3), 255-262, 2012. DOI
2. Lopresti, A.L. and Smith, S.J. Ashwagandha (Withania somnifera) for the treatment and enhancement of mental and physical conditions: a systematic review of human trials. Journal of Herbal Medicine, 28, 100434, 2021. DOI
3. Bachour, G. et al. Effects of ashwagandha supplements on cortisol, stress, and anxiety levels in adults: a systematic review and meta-analysis. BJPsych Open, 11(S1), 2025. DOI
4. Albalawi, A.A. et al. Dual impact of ashwagandha: significant cortisol reduction but no effects on perceived stress. A systematic review and meta-analysis. Nutrition and Health, 2025. DOI
5. Smith, S.J., Lopresti, A.L. and Fairchild, T.J. Exploring the efficacy and safety of a novel standardised ashwagandha root extract in adults experiencing high stress and fatigue: a randomized, double-blind, placebo-controlled trial. Journal of Psychopharmacology, 37(11), 1091-1104, 2023. DOI
6. Sarris, J. et al. Clinician guidelines for the treatment of psychiatric disorders with nutraceuticals and phytoceuticals: the WFSBP and CANMAT taskforce. The World Journal of Biological Psychiatry, 23(6), 424-455, 2022. DOI
7. Bjornsson, H.K. et al. Ashwagandha-induced liver injury: a case series from Iceland and the US Drug-Induced Liver Injury Network. Liver International, 40(4), 825-829, 2020. DOI
8. National Institutes of Health, Office of Dietary Supplements. Ashwagandha: is it helpful for stress, anxiety, or sleep? Health professional fact sheet, updated 2025. Link
9. Food Standards Agency. Summary of responses to call for evidence on ashwagandha, 2026. Link

This article is for informational purposes only and is not intended as medical advice, nor as a description of any particular product. It discusses published third-party research on the botanical Withania somnifera. Food supplements are not a substitute for a varied, balanced diet and a healthy lifestyle. Individual responses vary. Ashwagandha is not suitable for everyone, including during pregnancy and breastfeeding, and it may interact with prescribed medication. Always consult a qualified healthcare professional before starting or changing any supplement routine, particularly if you are taking medication or have a diagnosed health condition.