KSM-66 Ashwagandha — Complete Evidence Guide 2026

What Is KSM-66?

KSM-66 is made only from ashwagandha root using a water-based extraction its maker describes as "full-spectrum", and it is standardized to 5% withanolides. Other extracts differ: Sensoril, for example, uses root and leaf and is studied at lower doses (125 to 500 mg a day), mainly for stress and sleep. Research on one extract doesn't automatically apply to another, so check which extract and dose a study used.

Published Trials

• Stress (Chandrasekhar et al., 2012): in a 60-day trial of 64 adults with chronic stress, 300 mg twice daily lowered stress scores, and serum cortisol fell about 28% from baseline.
• Strength and testosterone (Wankhede et al., 2015): in 57 young men doing 8 weeks of resistance training, 300 mg twice daily led to bigger strength gains and a larger testosterone rise than placebo (about 96 vs 18 ng/dL), though end-of-study levels did not differ significantly between groups and the paper contains some inconsistencies.
• Sleep (Langade et al., 2019): in 60 adults with insomnia, 300 mg twice daily for 10 weeks led to falling asleep faster and more time in bed actually asleep than placebo, measured with a wrist sleep tracker. A 2021 meta-analysis of five sleep trials, mostly KSM-66, found clearer benefits at 600 mg a day, after at least 8 weeks, and in people with insomnia.

These trials were small, run mostly in India, and the extract was supplied by its manufacturer. Treat the results as encouraging rather than proof.

Safety

Ashwagandha is usually well tolerated in short trials, with stomach upset and drowsiness the most common complaints. It has been linked to rare cases of liver injury (stop and see a doctor if you notice yellow skin, dark urine or itching) and can raise thyroid hormone levels. It may interact with thyroid, diabetes, blood pressure, sedative and immunosuppressant medicines, isn't for pregnancy, and its safety beyond about three months isn't well studied. Our guide to ashwagandha side effects in men covers this in detail.

Products We Review That Contain KSM-66

Testosil contains 300 mg of KSM-66 per 4-capsule serving, so the 600 mg a day used in the strength and stress trials requires its maximum two servings. Two servings would double zinc to 80 mg and vitamin D to 8,000 IU a day, twice the adult upper limits, so don't take two servings without a doctor's advice. CortiSync contains Sensoril (300 mg), not KSM-66, and TestRX does not list ashwagandha.

Frequently Asked Questions

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