Ashwagandha has measurable effects on stress hormones, sleep, physical performance, and testosterone levels, backed by a growing body of clinical trials. Most people take it to lower stress and improve sleep, and the evidence supports both uses, though the benefits take several weeks to fully kick in and the supplement carries some risks worth knowing about.
How It Lowers Stress and Anxiety
Ashwagandha’s most well-studied effect is its ability to reduce cortisol, your body’s primary stress hormone. In a controlled trial of 60 healthy but mildly anxious adults, taking 240 mg daily for just 15 days produced a 23% drop in morning cortisol levels, compared to virtually no change in the placebo group. The supplement appears to work by interacting with the body’s stress-response system (the loop between your brain and adrenal glands that regulates cortisol output) and by influencing GABA, a brain chemical that promotes calm and relaxation.
The downstream effect on how people actually feel is significant. In one 60-day study, participants saw their scores on a standard stress questionnaire drop by 70%, and their anxiety scores fell by the same margin. Multiple trials using doses ranging from 125 mg to 500 mg per day have consistently shown improved psychological well-being compared to placebo, with higher doses not always outperforming lower ones.
Sleep Improvements
A meta-analysis of five trials, covering 372 adults with and without insomnia, found that ashwagandha meaningfully reduced the time it takes to fall asleep and increased total sleep duration. The effect was moderate in size but consistent across studies, with essentially no variation between trials. People with insomnia tended to see larger benefits than healthy sleepers.
Sleep improvements were most prominent at doses of 600 mg per day and when supplementation lasted at least 8 weeks. If you’re considering ashwagandha primarily for sleep, expect a gradual shift rather than an immediate sedative effect.
Physical Performance and Endurance
Ashwagandha has a modest but real effect on aerobic capacity. A systematic review and meta-analysis found that supplementation increased VO2 max (a measure of how efficiently your body uses oxygen during exercise) by an average of about 3 mL/kg/min in healthy adults and athletes. That’s a meaningful bump, roughly equivalent to several weeks of additional cardio training for a moderately fit person.
The performance benefits extend beyond endurance. Several trials have reported improvements in strength and recovery, though the size of these effects varies depending on the population studied and the training program involved.
Testosterone and Hormonal Changes
In a randomized crossover study of aging, overweight men, ashwagandha supplementation led to a 14.7% increase in testosterone and an 18% increase in DHEA-S, a precursor hormone that supports testosterone production. Both changes were statistically significant compared to placebo. When participants stopped taking ashwagandha, their hormone levels dropped back down, suggesting the effect depends on continued use.
These hormonal shifts are relevant for men experiencing age-related declines in energy and vitality, though ashwagandha is not a replacement for medical treatment of clinically low testosterone.
Cognitive Effects
A single 400 mg dose of ashwagandha improved working memory, sustained attention, and response speed in a controlled trial. Participants who took ashwagandha maintained their reaction times over hours of testing, while those on placebo got progressively slower as mental fatigue set in. The benefits were most noticeable on more demanding cognitive tasks: as the complexity of memory challenges increased, the gap between ashwagandha and placebo widened.
The practical takeaway is that ashwagandha appears to help the brain resist fatigue during prolonged mental effort. Whether this translates into noticeable day-to-day cognitive gains with long-term use is less well established than its stress and sleep benefits.
How Long It Takes to Work
Most clinical trials run 6 to 12 weeks, and the evidence suggests that 8 weeks is the minimum duration to see the full range of benefits, particularly for sleep. Some effects show up sooner: cortisol reductions have been measured after just 15 days, and acute cognitive benefits appear within hours of a single dose. Stress and anxiety improvements typically become significant by 6 to 8 weeks of daily use.
Doses used in research range from 125 mg to 600 mg per day, with most trials using standardized root or root-and-leaf extracts. The two most common branded extracts in clinical research are KSM-66 (a root extract) and Sensoril (a root-and-leaf extract), and dosing varies between them because of differences in concentration.
Side Effects and Safety Concerns
Common side effects are mild and digestive: nausea, stomach discomfort, and loose stools. These tend to resolve on their own or with a lower dose. The more serious concern is liver injury. Cases of ashwagandha-induced liver damage have been reported in Japan, Iceland, India, and the United States. Affected patients developed jaundice, elevated liver enzymes, and in some cases acute hepatitis. In at least one case, a patient had increased his dose to two or three times the recommended amount before being hospitalized. Most patients recovered after stopping the supplement, though recovery took up to eight months in some cases.
These liver cases are rare relative to the millions of people who take ashwagandha, but they’re real and worth taking seriously, especially if you use other supplements or medications that stress the liver.
Who Should Avoid It
The National Institutes of Health specifically recommends against ashwagandha for people with autoimmune disorders or thyroid conditions. Because ashwagandha can stimulate thyroid hormone production, it may interfere with thyroid medications and push levels outside a safe range. It also has potential interactions with diabetes medications, blood pressure drugs, immunosuppressants, sedatives, and anti-seizure medications. If you’re scheduled for surgery, you should stop taking it beforehand, as it may interact with anesthesia and affect blood pressure regulation.
The concern about long-term use and the body’s stress-response system is also worth noting. Because ashwagandha actively suppresses cortisol, prolonged use at higher doses could theoretically lead to the adrenal glands producing less cortisol on their own. The active compounds in ashwagandha may interfere with genes that encode the enzymes responsible for making stress hormones, which raises questions about what happens when you stop taking it after months or years of continuous use.