Ashwagandha (KSM-66) — the cortisol study guide
Ashwagandha (Withania somnifera) is the most-studied adaptogen in modern research. The KSM-66 extract — a full-spectrum root, standardised to 5% withanolides — is the form used in the majority of human trials. The trial-validated dose for stress, sleep and cortisol reduction is 300–600 mg of KSM-66 daily for 60+ days.
What the trials actually show
Across >15 randomised controlled trials, KSM-66 at 600 mg/day for 8 weeks reduced morning serum cortisol by 20–30% and improved Perceived Stress Scale scores by 30–44% vs placebo (Chandrasekhar et al., 2012; Salve et al., 2019; Lopresti et al., 2019). Sleep quality, measured by Pittsburgh Sleep Quality Index, improves on the same dose at 8 weeks.
Why root extract beats leaf
Most cheap SA ashwagandha is leaf or whole-plant powder. KSM-66 is root-only, standardised to a clinically meaningful 5% withanolide content. It is the form 90%+ of published cortisol research uses. Vivid uses KSM-66 from Ixoreal Biomed (India) — the original patented extract.
How to take it
Start with 300 mg KSM-66 once daily for 7 days; assess. Step up to 600 mg/day (300 mg morning + 300 mg evening, or 600 mg morning) for 8 weeks before judging effect. Take with food. Effects on stress, sleep and recovery are cumulative, not acute.
Who should be careful
Avoid in pregnancy. Speak to your doctor if you have an autoimmune condition (lupus, Hashimoto's), are on thyroid medication or immunosuppressants, or take sedatives. Stop 2 weeks before surgery.
Ashwagandha FAQ
What's the right ashwagandha dose?
300–600 mg of standardised KSM-66 root extract daily for 8 weeks before judging effect. Most SA brands underdose at 100–200 mg of generic leaf powder.
When will I feel it?
Stress and sleep benefits typically appear at 4–8 weeks of consistent daily dosing. It is not an acute, take-and-feel-it supplement.
Is KSM-66 better than Sensoril?
Sensoril is leaf + root extract standardised to 10% withanolides at a lower dose (125 mg). Both have human trials. KSM-66 has more cortisol-specific data in healthy adults.
Can I take it long-term?
Most clinical trials run 60–90 days. Long-term safety data is limited; consider a 2-week break after 12 weeks of continuous use.
Why is it not safe in pregnancy?
Traditional and modern guidance both list ashwagandha as a uterine stimulant. Avoid during pregnancy and while trying to conceive.