Ashwagandha is one of the most-studied adaptogenic herbs, and KSM-66 is its most-studied extract. Here is what the human clinical trials actually show — along with the safety details that matter.
What Is Ashwagandha
Withania somnifera is an adaptogenic herb used in Ayurvedic medicine for over 3,000 years. KSM-66 is a specific root extract standardized to at least 5% withanolides — the active compounds — and it has the largest body of human trial data of any ashwagandha extract.
Evidence — Stress and Cortisol
A 2012 randomized controlled trial (Chandrasekhar et al., Indian Journal of Psychological Medicine, 64 subjects with chronic stress) found that KSM-66 at 300mg twice daily for 60 days significantly reduced serum cortisol (−27.9% versus placebo, p<0.001) and improved Perceived Stress Scale scores. A 2021 trial (Langade et al., Cureus) found that 300mg twice daily for 8 weeks significantly improved sleep quality (PSQI score), mental alertness, and morning cortisol.
Evidence — Testosterone and Male Health
A pilot study (Ambiye et al., Evidence-Based Complementary and Alternative Medicine, 46 healthy males) found that KSM-66 at 300mg twice daily for 90 days significantly increased testosterone (+17% versus +4% with placebo, p=0.01) and DHEA-S levels. As a pilot study, it warrants replication in larger trials.
Evidence — Physical Performance
A 2015 randomized controlled trial (Wankhede et al., Journal of the International Society of Sports Nutrition, 57 male subjects) found that KSM-66 at 300mg twice daily for 8 weeks significantly improved VO2 max, muscle strength, and recovery compared with placebo.
Dosing
300–600mg of KSM-66 daily. Most trials use 300mg twice daily or 600mg once daily. It typically requires 4–8 weeks of consistent use before the full effect appears. BioPerine (piperine) may enhance absorption.
Safety
Ashwagandha is well-tolerated in most studies lasting up to 6 months, with rare reports of GI discomfort and drowsiness. One effect deserves specific attention: ashwagandha may increase T3 and T4 thyroid hormone levels, so caution is required in people with hyperthyroidism or anyone on thyroid medication. Because women are disproportionately affected by subclinical thyroid dysfunction, any woman with a history of thyroid issues or on thyroid medication should have TSH monitored when starting ashwagandha.
Contraindications
- Pregnancy: ashwagandha has uterine-stimulant properties — avoid.
- Autoimmune conditions: a theoretical concern exists about immune stimulation.
- Hyperthyroidism or thyroid medication: physician consultation required.
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Nutricost KSM-66 delivers 600mg of the clinically studied extract with BioPerine for enhanced absorption:
View Ashwagandha KSM-66 on Amazon →Sources
- Chandrasekhar et al. (2012). Indian Journal of Psychological Medicine.
- Langade et al. (2021). Cureus.
- Ambiye et al. Evidence-Based Complementary and Alternative Medicine.
- Wankhede et al. (2015). Journal of the International Society of Sports Nutrition.