Ashwagandha is one of the most well-studied herbal supplements available, with clinical evidence supporting benefits for stress, sleep, physical performance, and cognitive function. Most trials use standardized root extracts at doses of 250 to 600 mg per day, and meaningful results typically appear after about 8 weeks of consistent use.
Stress and Cortisol Reduction
The strongest evidence for ashwagandha centers on stress relief. A systematic review and meta-analysis published in BJPsych Open found that 8 weeks of supplementation produced significant reductions in both perceived stress scores and cortisol levels. Cortisol is the hormone your body releases under stress, and chronically elevated levels are linked to weight gain, poor sleep, and immune suppression. Participants taking ashwagandha saw their stress scores drop by nearly 5 points on the Perceived Stress Scale, a standardized questionnaire used across psychology research.
These aren’t subtle effects. The cortisol reductions were statistically robust, and the benefits appeared consistently across multiple studies included in the analysis. This is the benefit most people notice first: a general sense of feeling less reactive to daily pressures, with fewer of the physical symptoms that come with being chronically wound up.
Better Sleep Quality
Ashwagandha’s calming effect on the stress response carries over into sleep. Clinical trials using root extract (typically the KSM-66 brand at 600 mg per day) have shown improvements in both how quickly people fall asleep and how restful that sleep feels. The mechanism is straightforward: by lowering cortisol and calming the nervous system, ashwagandha helps your body shift into the relaxed state it needs for sleep onset.
If you’re someone who lies awake with a racing mind rather than someone with a diagnosed sleep disorder, this is where ashwagandha tends to help most. It’s not a sedative. It works by addressing the underlying stress chemistry that keeps you alert at night.
Physical Performance and Muscle Growth
Athletes and gym-goers have some reason to be interested. A meta-analysis of physical performance studies found consistent improvements across several measures. VO2 max, which reflects your body’s ability to use oxygen during exercise, improved by roughly 5 to 13% across multiple trials. That range represents meaningful gains in cardiovascular endurance.
Strength outcomes were even more striking in individual studies. One trial found that participants taking ashwagandha increased their bench press one-rep max by about 14% and squat one-rep max by 18%, compared to smaller gains in the placebo group. Another study reported significant increases in arm and thigh muscle size alongside strength gains. These trials typically lasted 8 to 12 weeks and involved participants who were also following resistance training programs, so ashwagandha appears to amplify the results of exercise rather than replace it.
The likely explanation involves ashwagandha’s effect on recovery. Lower cortisol means less muscle breakdown after workouts and a hormonal environment more favorable to building new tissue.
Cognitive Function and Reaction Time
A double-blind study in healthy adults found that a single dose of ashwagandha improved picture recognition speed and accuracy, with faster reaction times for correctly identifying images they’d seen before. After 30 days of daily supplementation, the benefits expanded: participants maintained their ability to correctly recall images and stay vigilant on attention tasks, while the placebo group’s performance declined over time.
Executive function, tested through tasks that require you to override automatic responses (like reading a color word printed in a different color), also showed trends toward improvement. The cognitive benefits appear to be partly about preventing the mental fatigue that accumulates during demanding tasks, keeping your brain sharper for longer rather than dramatically boosting raw intelligence.
Testosterone and Sexual Health
Ashwagandha may modestly increase testosterone in men. One randomized, placebo-controlled trial found that the supplement increased serum testosterone by roughly 15% compared to placebo, alongside improvements in sexual function scores. However, some inconsistencies in the study’s own data make that testosterone figure less certain than the sexual function improvements, which were more clearly supported.
Research in women is more limited but points in a positive direction. A study using a high-concentration root extract found improved sexual function scores in healthy women, suggesting the benefits aren’t exclusive to men. The mechanism likely involves ashwagandha’s broader effect on stress hormones, since elevated cortisol suppresses reproductive hormone production in both sexes.
Blood Sugar and Metabolic Health
Early clinical evidence suggests ashwagandha can lower fasting blood sugar by about 12% in people with type 2 diabetes. Animal studies have shown improvements in insulin sensitivity, glucose tolerance, and a reduction in HbA1c (a marker of long-term blood sugar control). Active compounds in the plant appear to reduce insulin resistance partly by increasing adiponectin, a hormone that helps your cells respond to insulin more effectively.
These findings are promising but come from smaller studies. The blood sugar benefit is real enough to matter for one important reason: if you’re already taking diabetes medication, ashwagandha could push your blood sugar lower than expected. That’s something to be aware of before combining the two.
Dosage and Extract Types
Not all ashwagandha supplements are the same. The two most commonly studied extracts are KSM-66 and Sensoril, and they differ in composition. KSM-66 is a root-only extract, standardized to contain more than 5% withanolides (the active compounds). Sensoril uses both root and leaf material. Most clinical trials have used KSM-66 at doses of 250 to 600 mg per day, often split into two doses.
The 8-week mark is where most studies show clear, measurable results for stress and cortisol reduction. Some benefits, like acute improvements in reaction time, can appear after a single dose. Strength and endurance gains require the longer timeline of 8 to 12 weeks, consistent with the time it takes to see results from any training-related supplement. If you’ve been taking it for two months and notice nothing, it’s reasonable to conclude it’s not working for you.
Safety and Who Should Avoid It
Ashwagandha is generally well tolerated at the doses used in clinical research. The NIH’s National Center for Complementary and Integrative Health flags several specific groups who should not take it:
- People with thyroid disorders. Ashwagandha can alter thyroid hormone levels, which is dangerous if you have Hashimoto’s, Graves’ disease, or are taking thyroid medication.
- People with autoimmune conditions. Because ashwagandha stimulates immune activity, it can worsen conditions where the immune system is already overactive.
- People taking immunosuppressants. The supplement may counteract medications designed to dial down immune response.
- People about to have surgery. Its effects on the nervous system and hormones make it worth stopping before any scheduled procedure.
Rare cases of liver injury have been reported with ashwagandha use, though these appear uncommon at standard doses. Mild side effects like digestive discomfort and drowsiness are the most frequently noted complaints in clinical trials.