Ashwagandha and Cortisol: What the KSM-66 Trials Actually Found
KSM-66 is the branded ashwagandha root extract used in the clinical trials on stress and cortisol, standardised to a minimum 5% withanolides. The studied daily range is 300 to 600mg, and it has been shown to reduce cortisol in randomized trials. ONCE carries 600mg, the top of that range, alongside 300mg of magnesium glycinate and 200mg of L-theanine.
Cortisol became the most talked-about hormone on the internet, and the supplement market responded by selling magnesium for it. Magnesium is a genuinely useful mineral with a real role in stress physiology, but here is the part the marketing skips: ashwagandha is the ingredient the cortisol trials actually used.
What KSM-66 actually is
Ashwagandha is a plant. KSM-66 is a specific, standardised extract of it — and the distinction matters more here than with almost any other ingredient.
- Root only. Not leaf, not whole plant. The leaf contains a different withanolide profile and is cheaper to source.
- Standardised to a minimum 5% withanolides. Withanolides are the active compounds. Without a standardisation figure, "ashwagandha extract" is an unknown quantity.
- It is the material the trials used. When you read a study on ashwagandha and stress, there is a good chance it was run on this extract.
What the research measured
Randomized, placebo-controlled trials on standardised ashwagandha root extract have measured serum cortisol as an endpoint, and it has been shown to reduce cortisol in those trials, alongside improvements on validated stress questionnaires. The studied daily range sits between 300 and 600mg.
What we will not tell you is that it fixes your face, your waistline or your sleep debt. Those claims are everywhere in this category right now and they are not what the studies measured.
Why 600mg and not 300
| Daily dose | Status |
|---|---|
| Under 300mg | Below the commonly studied range. |
| 300mg | Bottom of the studied range. Supported. |
| 600mg — in ONCE | Top of the studied range. |
The rest of the stack
ONCE does not carry ashwagandha alone, because the stress research does not sit on one ingredient.
Magnesium as true bisglycinate at 300mg elemental — the gentle chelated form, not oxide. L-theanine at 200mg, studied for calm focus without sedation, which is why it pairs with coffee rather than fighting it. Glycine at 1g, which is also naturally sweet and does real work in the flavour system.
So the honest version of the cortisol pitch is not "this lowers your cortisol." It is: this contains the magnesium the market is selling you, plus the ingredient the cortisol studies were actually run on, at the top of its studied range, plus theanine.
ONCE launches as a 30-serving tub. One scoop into 12 to 16 ounces of cold water, stir, drink it with breakfast. That is the entire routine, and it costs $50 a month. There is no caffeine in it, so it works at 6am or 6pm.
Common questions
What is KSM-66 ashwagandha?
KSM-66 is a branded ashwagandha extract made from the root only and standardised to a minimum of 5% withanolides. It is the extract used in much of the clinical research on ashwagandha, stress and cortisol. ONCE carries 600mg per serving, the top of the studied 300 to 600mg daily range.
How much ashwagandha should I take for stress?
The commonly studied daily range for standardised ashwagandha root extract is 300 to 600mg. ONCE uses 600mg, the top of that range.
Does ashwagandha lower cortisol?
Randomized placebo-controlled trials on standardised ashwagandha root extract have measured serum cortisol as an endpoint and shown reductions relative to placebo. That is a measured research finding rather than a guarantee of an individual result.
Is ashwagandha better than magnesium for stress?
They are not competing. Magnesium has a real role in stress physiology, but ashwagandha is the ingredient the cortisol trials were run on. ONCE includes both, plus 200mg of L-theanine: 600mg KSM-66, 300mg magnesium glycinate.
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. This article is educational and is not medical advice; consult a physician before starting any supplement.