KSM-66 Ashwagandha: What the Research Shows in 2026

Understanding the KSM-66 Extract

To make KSM-66, its maker uses a water-based extraction on ashwagandha root alone, and calls the result "full-spectrum". The standardization is 5% withanolides. Other extracts aren't the same. Sensoril combines root and leaf, and researchers have tested it at lower doses (125 to 500 mg a day), mainly for stress and sleep. What holds for one extract may not hold for another, so always note which extract and dose a study used.

Published Trials

• Stress (Chandrasekhar et al., 2012): Over 60 days, 64 adults with chronic stress took 300 mg twice daily. Their stress scores dropped, and serum cortisol fell about 28% from baseline.
• Strength and testosterone (Wankhede et al., 2015): Researchers followed 57 young men through 8 weeks of resistance training. Those taking 300 mg twice daily gained more strength than placebo and had a bigger testosterone rise (about 96 vs 18 ng/dL). By the end of the study, levels didn't differ significantly between groups, and the paper has some inconsistencies.
• Sleep (Langade et al., 2019): 60 adults with insomnia took 300 mg twice daily for 10 weeks. Measured with a wrist sleep tracker, they fell asleep faster than on placebo and slept for more of their time in bed. Pooling five sleep trials, mostly KSM-66, a 2021 meta-analysis saw clearer benefits at 600 mg a day, after at least 8 weeks, and in people with insomnia.

Small sample sizes, a mostly Indian setting and a maker-supplied extract limit all of these trials. Call the results encouraging and stop short of proof.

Safety

In short trials people mostly tolerated ashwagandha, with stomach upset and drowsiness the leading complaints. Rare liver injury has been reported, so if your skin turns yellow, your urine darkens or you itch, stop taking it and see a doctor. It can also raise thyroid hormone levels, and it may interact with thyroid, diabetes, blood pressure, sedative and immunosuppressant medicines. Don't use it in pregnancy. Safety beyond about three months isn't well studied. For detail, read our guide to ashwagandha side effects in men.

Reviewed Products With KSM-66

Testosil has 300 mg of KSM-66 in each 4-capsule serving, which means the 600 mg a day used in the strength and stress trials takes 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) rather than KSM-66, while TestRX doesn't list ashwagandha at all.

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