Your Cortisol Has a Shape. What Did the Ashwagandha Trials Actually Measure?

You do not really have a cortisol level. You have a cortisol curve. It climbs steeply in the first half hour after you wake, drifts down through the afternoon and evening, and reaches its lowest point at night.

That sounds like a technicality. It turns out to be one of the most useful things to understand when reading the ashwagandha research, because nearly every trial that reports a cortisol result is reporting a single point on that curve, taken once at the start and once at the end. Where on the curve that point sits, and how carefully it was timed, changes what the result can tell you.

If you want the broader picture first, our earlier piece, Ashwagandha and Cortisol: What the Research Actually Shows, covers the main trials and meta-analyses. This one goes a level deeper, into what was actually measured.

The Shape of a Normal Day

Cortisol is released by the adrenal glands in a daily rhythm. The most striking feature of that rhythm happens right after waking. Over the first 30 to 45 minutes, cortisol output rises sharply. Researchers call this the cortisol awakening response, and it sits on top of the broader day-night rhythm as a distinct event of its own.

Nobody is entirely sure what it is for. One leading idea, set out in a 2009 review by Fries, Dettenborn and Kirschbaum, is that the size of the morning surge is shaped partly by anticipation of the day ahead. It is also known to vary with sex, health status, health behaviour and how stressed a person feels.

After that morning peak, levels decline across the day. The difference between morning and evening is called the diurnal slope, and it is where things get interesting.

Why the Shape May Matter More Than the Number

In 2017, a systematic review and meta-analysis led by Emma Adam at Northwestern University pulled together 179 associations from 80 studies. The question was simple: is the steepness of a person's daily cortisol slope linked to their health?

The answer was yes, modestly but consistently. Flatter slopes, meaning less of a drop from morning to evening, were associated with poorer health across the studies as a whole, and in 10 of the 12 categories of emotional and physical health the authors examined. The strongest link was with immune and inflammation outcomes.

Two caveats matter. These are associations, not proof of cause and effect, and the authors themselves discuss whether a flat slope is a marker of something going wrong or part of the mechanism. And the effect sizes were small to moderate. But the direction is telling. On this evidence, what seems to matter is not having low cortisol. It is having a well-shaped day: a strong morning rise and a proper fall by evening.

A healthy cortisol rhythm has a high point. Lower is not automatically better. A clear rise and a clear fall appear to matter more than any single reading.

Three Different Things Called "Cortisol"

When a study says it measured cortisol, it could mean one of three quite different things.

There is also the question of where it is measured. A blood test captures total cortisol in circulation and is usually done in a clinic. Saliva reflects the unbound, active fraction and can be collected at home, which makes repeated sampling easier but harder to supervise.

What the Ashwagandha Trials Measured

Read the methods sections and a pattern emerges quickly. Almost every trial took the snapshot.

In Chandrasekhar and colleagues' 2012 trial, the one most often quoted, serum cortisol was measured on a morning at the start of the study and again at the end, on day 60. In Lopresti and colleagues' 2019 study of 60 stressed adults, a fasting blood sample was taken at around 8am at the start and the end, and ashwagandha was associated with a greater reduction in morning cortisol than placebo. In a 90-day trial published in 2021 by Gopukumar and colleagues, serum cortisol was drawn between 9am and 11am. A 2023 trial by Majeed and colleagues, using an extract combined with piperine, measured morning salivary cortisol and reported a greater reduction with ashwagandha than with placebo.

Each of these is a reasonable design for the question it set out to answer. But each tells you about one moment. None of them can tell you whether the shape of the curve changed.

The Problem With a Morning Snapshot

The morning is exactly when cortisol is moving fastest. A sample taken at waking and a sample taken 30 minutes later can look like two different people. That means small differences in timing, from one visit to the next or one participant to the next, can add noise to the result, or even create a difference that has nothing to do with the supplement.

A 2019 trial by Lopresti, Drummond and Smith shows the issue clearly. Overweight men aged 40 to 70 collected saliva at home within 15 minutes of waking, before eating, drinking or brushing their teeth. After eight weeks, the ashwagandha group showed no statistically significant difference in cortisol compared with placebo. To their credit, the authors pointed out the limitation themselves: collection times could not be properly monitored because samples were taken at home, and saliva readings are vulnerable to rapid changes across the morning.

This is not a niche concern. The International Society of Psychoneuroendocrinology published expert guidelines in 2016 on how to measure the awakening response properly, with objective checks on the exact time of waking and sampling as a central recommendation. When the same group reviewed the field in 2022, they found little improvement in how often those checks were actually used.

What Nobody Has Measured Yet

We searched PubMed for randomised trials of ashwagandha that mapped the cortisol awakening response or the full diurnal slope. We did not find one. That may change, and if a trial has been missed we would like to hear about it. But on what is currently indexed, the shape of the curve is the part of the cortisol story that has not been tested.

That gap matters because of the point made earlier. If a healthy rhythm includes a strong morning rise, then a lower morning reading on its own is ambiguous. It might reflect a calmer system. It might reflect a flatter curve. It might reflect when the sample was taken. A snapshot cannot separate those possibilities. Only repeated, carefully timed sampling can.

A Different Question: The Spike

A small number of newer trials have started asking a different question. Rather than whether ashwagandha lowers a resting level, they ask whether it changes how cortisol reacts to pressure.

In a 28-day trial published in August 2026 in Advances in Therapy, Lopresti and colleagues gave 60 stressed adults either a low-dose branded ashwagandha extract or a placebo. On day 28, participants went through the Socially Evaluated Cold-Pressor Test, which involves holding a hand in ice-cold water while being watched and evaluated. Salivary cortisol rose in the placebo group but stayed relatively stable in the ashwagandha group, a difference that only just reached statistical significance. Most of the other physiological measures showed no significant difference, and the authors describe the findings as preliminary.

A separate 2026 trial in team sports athletes during pre-season training found that salivary cortisol, measured after training, rose significantly over 42 days in female athletes taking placebo. The authors describe ashwagandha as having a stabilising effect on this marker.

Neither result settles anything. But together they point towards a more precise question than "does it lower cortisol?" The more useful question may be whether it changes the size of the spike when life applies pressure, while leaving the healthy daily rhythm intact. That is testable. It just has not been tested well yet.

Not Every Trial Found a Change

It is worth repeating that the snapshot results are not unanimous either. Beyond the 2019 study in older men described above, a 2025 trial of a different branded extract in 90 adults with mild to moderate stress, published in Advances in Therapy, found improvements on stress questionnaires but no significant difference between groups in serum cortisol over 84 days.

The pooled evidence still leans towards lower morning cortisol in stressed adults, as our earlier article sets out. But a pattern of mostly positive results, measured mostly one way, with a few clear exceptions, is a reason for interest rather than certainty.

Safety, and Who Should Not Take It

Ashwagandha appears to be well tolerated in trials of up to about three months, with mild side effects such as stomach upset, loose stools, nausea and drowsiness. Longer-term safety data is limited. Case reports have linked it to liver injury, and there are reports of effects on thyroid function. It may interact with medication for thyroid conditions, diabetes and blood pressure, as well as immunosuppressants and sedatives.

In the UK, the Food Standards Agency has referred ashwagandha to the Committee on Toxicity for a formal risk assessment. As of October 2026, the Committee has discussed a third draft statement but has not published a conclusion. In the Netherlands, a draft rule reported in October 2026, and now open for consultation, would ban ashwagandha leaf and leaf-derived preparations, while allowing root products with a caution statement. Ashwagandha is not banned in the UK and remains legally available.

If you are pregnant or breastfeeding, under 18, have a thyroid or liver condition, or take any prescribed medication, speak to your doctor or pharmacist before taking it.

The Honest Summary

The cortisol research on ashwagandha is real, and the morning snapshot results lean in a consistent direction in stressed adults. But cortisol is a rhythm, and the research has mostly looked at one moment in it. A lower morning reading could mean several different things, and the studies that would tell them apart have not yet been done.

That is not a reason to dismiss the evidence. It is a reason to read it precisely. When you next see a headline that says a supplement "lowers cortisol", it is worth asking three questions. Measured when? Measured how? And was the goal ever to make it lower in the first place?

References

1. Fries, E., Dettenborn, L. and Kirschbaum, C. The cortisol awakening response (CAR): facts and future directions. International Journal of Psychophysiology, 72(1), 67-73, 2009. DOI
2. Stalder, T. et al. Assessment of the cortisol awakening response: expert consensus guidelines. Psychoneuroendocrinology, 63, 414-432, 2016. DOI
3. Stalder, T. et al. Evaluation and update of the expert consensus guidelines for the assessment of the cortisol awakening response (CAR). Psychoneuroendocrinology, 146, 105946, 2022. DOI
4. Adam, E.K. et al. Diurnal cortisol slopes and mental and physical health outcomes: a systematic review and meta-analysis. Psychoneuroendocrinology, 83, 25-41, 2017. DOI
5. 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
6. Lopresti, A.L., Smith, S.J., Malvi, H. and Kodgule, R. An investigation into the stress-relieving and pharmacological actions of an ashwagandha (Withania somnifera) extract: a randomized, double-blind, placebo-controlled study. Medicine, 98(37), e17186, 2019. DOI
7. Lopresti, A.L., Drummond, P.D. and Smith, S.J. A randomized, double-blind, placebo-controlled, crossover study examining the hormonal and vitality effects of ashwagandha (Withania somnifera) in aging, overweight males. American Journal of Men's Health, 13(2), 2019. DOI
8. Gopukumar, K. et al. Efficacy and safety of ashwagandha root extract on cognitive functions in healthy, stressed adults: a randomized, double-blind, placebo-controlled study. Evidence-Based Complementary and Alternative Medicine, 2021, 8254344. DOI
9. Majeed, M., Nagabhushanam, K. and Mundkur, L. A standardized ashwagandha root extract alleviates stress, anxiety, and improves quality of life in healthy adults by modulating stress hormones: results from a randomized, double-blind, placebo-controlled study. Medicine, 102(41), e35521, 2023. DOI
10. Lopresti, A.L. et al. An examination into the anti-stress and anti-fatigue effects of an ashwagandha extract (Ashwa.30) in stressed adults: a randomised, double-blind, placebo-controlled trial. Advances in Therapy, 2026. DOI
11. Coope, O.C. et al. Ashwagandha root extract stabilises physiological stress responses in male and female team sports athletes during pre-season training. Nutrients, 18(2), 2026. DOI
12. Mahadevan, M. et al. A new ashwagandha formulation (Zenroot) alleviates stress and anxiety symptoms while improving mood and sleep quality: a randomized, double-blind, placebo-controlled clinical study. Advances in Therapy, 42(10), 5238-5254, 2025. DOI
13. National Institutes of Health, Office of Dietary Supplements. Ashwagandha: is it helpful for stress, anxiety, or sleep? Health professional fact sheet. Link
14. Committee on Toxicity of Chemicals in Food, Consumer Products and the Environment. 8th September 2026 meeting papers (third draft statement on ashwagandha). GOV.UK, 2026. Link
15. NutraIngredients. Ashwagandha, huperzia targeted under proposed Dutch supplement rules. 6 October 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.