What published trials of ashwagandha extracts such as KSM-66 and Sensoril found for stress, cortisol, sleep and testosterone, the doses they used and the safety cautions.
For stress, the evidence is reasonably encouraging: several small placebo-controlled trials of standardized extracts (mainly KSM-66 and Sensoril) found lower stress scores and lower cortisol after about 8 weeks. Evidence for sleep is moderate, and for testosterone it rests on a few small trials in men. Results apply to the extract and dose that was tested, and most trials were small and supported by the extract makers.
Most ashwagandha research uses branded extracts. In a 60-day trial of 64 adults with chronic stress (Chandrasekhar et al., 2012), people taking 300 mg of KSM-66 twice daily reported lower stress scores than the placebo group, and their serum cortisol fell about 28% from baseline. In a 2015 trial (Wankhede et al.), 57 young men doing resistance training took 300 mg of KSM-66 twice daily for 8 weeks and had bigger strength gains and a larger rise in testosterone than the placebo group.
A different extract, Sensoril (root and leaf), was tested in a 2024 trial of 98 stressed adults: 125, 250 or 500 mg a night for 8 weeks all lowered perceived stress and plasma cortisol more than placebo. For sleep, the NIH Office of Dietary Supplements describes a meta-analysis of five trials that found clearer benefits at 600 mg a day, after at least 8 weeks, and in people with insomnia.
The limits are real: these trials were small, run mostly in India, often funded or supplied by the extract makers, and none lasted more than about three months. The 2015 strength paper also has inconsistencies between its abstract and its results.
Results from one extract don't automatically transfer to another. KSM-66 (root only) is usually studied at 300 to 600 mg a day, while Sensoril (root and leaf, higher withanolide content) is studied at 125 to 500 mg a day. No trial has compared them head to head. When you compare products, check which extract is used and whether the daily amount matches a dose that was actually tested.
Ashwagandha is usually well tolerated in short trials, but it has been linked to rare cases of liver injury and can raise thyroid hormone levels. It may interact with diabetes, thyroid, blood pressure, sedative and immunosuppressant medicines, and it isn't for pregnancy. Long-term safety beyond about three months is not known. Our ashwagandha side effects guide covers who should avoid it.
Testosil is our top pick among testosterone-support formulas. Each 4-capsule serving contains 300 mg of KSM-66 alongside D-aspartic acid, zinc, vitamin D and other ingredients, with every dose disclosed. The 600 mg a day used in the KSM-66 trials would take two servings, which would also push zinc and vitamin D past adult upper limits. Testosil itself has not been tested in a trial. It is sold with an advertised lifetime money-back guarantee; check the conditions before you buy.