Ashwagandha has become the default answer to almost every stress question online β take the root, watch your cortisol fall, feel calmer by Tuesday. The reality is more interesting than that, and a bit messier. There's genuine clinical research behind ashwagandha and cortisol. It's just worth knowing what the studies actually measured, at what dose, and where the evidence quietly runs out.
What cortisol is actually doing when you're stressed
Cortisol is a hormone released by your adrenal glands as part of the hypothalamus-pituitary-adrenal (HPA) axis β the body's built-in stress-response system. In short bursts, it's useful: it sharpens focus and mobilises energy to get you through whatever's in front of you. The problem is when it stays elevated for weeks on end, quietly chipping away at sleep, mood, and patience. Ashwagandha is classed as an adaptogen, a term for plants thought to help the body regulate that HPA-axis response rather than switch it off entirely.[1]
What the trials on ashwagandha and cortisol actually show
The evidence base here is bigger than most supplements get. A steady run of randomised, placebo-controlled trials β mostly small, mostly running 6 to 12 weeks β has tested standardised ashwagandha root extracts against placebo in adults reporting everyday stress. Across them, daily doses ranging from 240mg to 600mg have produced measurable reductions in serum cortisol compared with placebo, with the larger effects generally showing up at 500-600mg/day.[1]
One of the better-known trials puts this in concrete numbers. Sixty stressed adults took either a standardised 240mg ashwagandha extract or a placebo, once daily, for 60 days.[2]
That's one study, on one specific extract, at one specific dose β not every ashwagandha capsule on a shelf, and not a promise that any particular product will replicate it exactly. But it's a fair, real example of what "ashwagandha lowers cortisol" is actually built on.
Feeling less stressed and testing lower for cortisol aren't automatically the same thing
Here's the part that tends to get skipped. A 2025 systematic review and meta-analysis pooling 15 trials and 873 adults found ashwagandha produced statistically significant reductions in cortisol, and in validated stress and anxiety scores.[3] But a separate meta-analysis of eight trials in 488 adults found something messier: cortisol came down, yet people's own ratings of how stressed they felt didn't shift any more than the placebo group's did.[4]
Cortisol dropping on a lab test and feeling calmer are not automatically the same thing, and the research doesn't fully agree on how tightly the two are linked. Both findings can be true at once β a biological marker shifting doesn't guarantee a felt difference for every person, especially over trial windows as short as six to eight weeks. It's a reasonable case for cautious optimism, not a guarantee of how you personally will feel.
Dose and extract matter more than the word "ashwagandha" on the label
This is where most of the confusion comes from. "Ashwagandha" isn't one standardised thing. Trials have used root extracts, root-and-leaf extracts, and different proprietary formulas β KSM-66, Shoden and Sensoril among them β standardised to different withanolide percentages, at doses ranging from 120mg to well over 1,000mg a day. A taskforce from the World Federation of Societies of Biological Psychiatry has provisionally recommended 300-600mg/day of a root extract standardised to 5% withanolides for generalised anxiety, while noting more data is still needed before that can become a stronger recommendation.[1]
- Which extract, not just "ashwagandha" β named, studied extracts like KSM-66 and Shoden have a trial history behind them; generic "root powder" usually doesn't.
- Withanolide standardisation β look for a stated percentage (commonly 5%), not just a milligram figure sitting on its own.
- Dose per serving β most of the stress research clusters around 300-600mg/day.
- Third-party testing β independent lab verification matters more for botanicals than most supplement categories, given how variable raw plant material can be.
Oxford Origins' Ashwagandha KSM-66 uses KSM-66 β the 12:1 full-spectrum root extract behind a good portion of the research above β in a single 1281mg daily capsule, boosted with a 95% piperine black pepper extract for absorption. Worth being precise here: the exact cortisol figures from any one trial won't map onto any one product, capsule for capsule. What KSM-66 gives you is an extract with an actual, named research trail behind it, rather than an unspecified "ashwagandha" sitting on an ingredients list.
If timing is the thing you're trying to get right β morning versus evening, with food or without β we've covered that in more depth in our guide to the best time to take ashwagandha.
Who should be cautious with ashwagandha
Ashwagandha has a reasonably good short-term safety record β trials running up to about three months report mostly mild side effects, things like an upset stomach or drowsiness.[1] That doesn't make it nothing, and it isn't right for everyone. It can affect thyroid hormone levels, so it needs caution if you have a thyroid condition. A small number of liver injury cases have been reported, generally at higher doses or alongside other medications.[1] It isn't recommended during pregnancy or while breastfeeding, and it may not be appropriate for men with hormone-sensitive prostate cancer, given its effect on testosterone in some trials.[1]
In the UK, herbal supplements including ashwagandha can be sold either as standard food supplements or, for some products, under the MHRA's Traditional Herbal Registration scheme, which sets safety and quality standards without requiring proof of effectiveness.[5] Neither route replaces a conversation with your GP, particularly if you're on other medication or managing an existing condition. We go into more detail on the regulatory side in our piece on ashwagandha's legal status in the UK.
None of this makes ashwagandha a fix for a stressful life β nothing in a capsule replaces sleep, boundaries, or an actual day off. What the research does support, cautiously, is a real physiological effect worth taking seriously, provided the extract, dose and person are the right match. That's the standard we've built the KSM-66 formula around: not the loudest claim on the shelf, just the ingredient that's actually been studied properly, at an amount that's actually shown up in the trials.
Frequently asked questions
How long does it take for ashwagandha to lower cortisol?
Most of the placebo-controlled trials run 6 to 12 weeks, and that's genuinely the timeframe to expect β this isn't a same-day effect. The 60-day trial mentioned above saw its biggest cortisol drop by the end of that period, not the first week. For more on timing, including whether morning or evening dosing makes a difference, see our guide on the best time to take ashwagandha.
Can you take ashwagandha every day, or does it need cycling?
Most of the clinical trials used daily dosing without a break, for up to around three months, without notable safety issues. There isn't strong evidence either way on cycling β taking planned breaks β and beyond about three months the research thins out considerably. Treat continuous long-term use as an open question rather than a settled one, and check in with your GP if you're taking it for months on end.
Is ashwagandha legal and safe to buy in the UK?
Yes β ashwagandha is legally sold in the UK, either as a food supplement or, for some products, under the MHRA's Traditional Herbal Registration scheme. That's a regulatory route around quality and safety standards, not a guarantee of effectiveness. We cover exactly how that works in our full piece on ashwagandha's legal status.
What's the difference between KSM-66, Sensoril and Shoden ashwagandha?
They're different proprietary extracts, made from different parts of the plant and standardised differently. KSM-66 is a root-only extract standardised to a minimum 5% withanolides and has one of the largest bodies of published research behind it. Sensoril uses root and leaf and tends to run at a higher withanolide concentration. Shoden is also a root extract, standardised differently again, and was the specific extract used in the 240mg cortisol trial referenced above. None is definitively "better" across the board β the honest answer is that each has its own, separate trial evidence, so it's worth checking which extract, not just the word "ashwagandha," backs whatever you're taking.
Sources
- NIH Office of Dietary Supplements β Ashwagandha Health Professional Fact Sheet, covering HPA-axis mechanism, dosing evidence, and safety data. https://ods.od.nih.gov/factsheets/Ashwagandha-HealthProfessional/
- Lopresti AL, Smith SJ, Malvi H, 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 (Baltimore) 2019 β cited for the 27.9% vs 7.9% cortisol figure. https://pubmed.ncbi.nlm.nih.gov/31517876/
- "Effects of Ashwagandha Supplements on Cortisol, Stress, and Anxiety Levels in Adults: A Systematic Review and Meta-Analysis." BJPsych Open, 2025 β 15 studies, 873 adults. cambridge.org
- Albalawi AA et al. "Dual impact of Ashwagandha: Significant cortisol reduction but no effects on perceived stress β A systematic review and meta-analysis." 2025 β cited for the cortisol/perceived-stress disconnect. journals.sagepub.com
- GOV.UK / MHRA β "Apply for a traditional herbal registration (THR)," cited for UK herbal supplement regulation. https://www.gov.uk/guidance/apply-for-a-traditional-herbal-registration-thr
At Oxford Origins, your wellbeing is our priority, and although we pride ourselves on our expertise in nutrition and supplementation, it's important to acknowledge the individuality of each person. Articles published by Oxford Origins are not intended to treat, diagnose, cure or prevent any disease, or replace the advice of your GP. We always recommend consulting with a healthcare provider if you encounter any health concerns, and we'll always be here to support you so you're never alone on your journey.
