Published trials of ashwagandha extracts such as KSM-66 and Sensoril looked at stress, cortisol, sleep and testosterone. Here are the results, the doses used and safety cautions.
Stress is where the evidence looks best. Several small placebo-controlled trials of standardized extracts (mainly KSM-66 and Sensoril) reported lower stress scores and lower cortisol at about 8 weeks. Sleep evidence is moderate, and a few small trials in men underpin the testosterone findings. Results hold only for the extract and dose tested, and the extract makers supported most of these small trials.
In the Chandrasekhar et al. (2012) trial, 64 adults with chronic stress took 300 mg of KSM-66 twice daily for 60 days. They reported lower stress scores than the placebo group, and their serum cortisol fell about 28% from baseline. A second study, Wankhede et al. (2015), gave 57 young men in resistance training the same dose, 300 mg twice daily, for 8 weeks. Strength gains and the rise in testosterone were both larger than with placebo.
Sensoril, which is made from root and leaf, got its own 2024 trial in 98 stressed adults. Whether they took 125, 250 or 500 mg a night for 8 weeks, perceived stress and plasma cortisol fell more than with placebo. On sleep, the NIH Office of Dietary Supplements points to a meta-analysis of five trials, where benefits were clearer at 600 mg a day, after at least 8 weeks, and in people with insomnia.
The limits are real. Trials were small, mostly run in India, and often funded or supplied by the extract makers. None lasted beyond about three months. The abstract and results of the 2015 strength paper also don't agree in places.
Another extract may behave differently, so don't carry results across. KSM-66 comes from root only and is usually studied at 300 to 600 mg a day. Sensoril comes from root and leaf, has a higher withanolide content, and is studied at 125 to 500 mg a day. Nobody has compared the two head to head. Before choosing a product, find out which extract it uses and whether its daily amount matches a dose that was actually tested.
Short trials found ashwagandha usually well tolerated. Even so, rare cases of liver injury have been linked to it, and it can raise thyroid hormone levels. Possible interactions include diabetes, thyroid, blood pressure, sedative and immunosuppressant medicines, and pregnancy rules it out. We don't know its safety beyond about three months. Who should avoid it is covered in our ashwagandha side effects guide.
Testosil is the testosterone-support formula we rank first. Four capsules make one serving, with 300 mg of KSM-66, D-aspartic acid, zinc, vitamin D and other ingredients, and every dose is disclosed. The KSM-66 trials used 600 mg a day, which would take two servings and also carry zinc and vitamin D beyond adult upper limits. Testosil hasn't been tested in a trial itself. An advertised lifetime money-back guarantee comes with it, so check the conditions before you buy.