Ashwagandha is an adaptogenic herb that primarily lowers cortisol, your body’s main stress hormone, while also improving sleep, supporting mild increases in testosterone, and boosting physical endurance. In clinical trials, it reduced cortisol levels by about 23% over eight weeks and cut anxiety scores nearly in half. Those are the headline effects, but the details matter because ashwagandha does different things at different doses, and it carries real risks for certain people.
How It Works in Your Body
Ashwagandha’s active compounds, called withanolides, interact with your stress response system at multiple levels. They appear to act directly on glucocorticoid receptors and influence the communication loop between your brain and adrenal glands (the system that controls cortisol release). They also boost the activity of GABA, a brain chemical that promotes calm and drowsiness, which partly explains the herb’s sedative quality.
This dual action, dampening the stress signal while simultaneously increasing a calming neurotransmitter, is what sets ashwagandha apart from a simple sedative. It doesn’t just make you sleepy. It lowers the baseline level of stress hormones circulating in your blood, which has downstream effects on sleep, mood, inflammation, and hormonal balance.
Stress and Anxiety Reduction
The strongest evidence for ashwagandha is in stress and anxiety. In a randomized, placebo-controlled study, participants taking ashwagandha saw a 41% reduction in anxiety scores over the study period, compared to a 24% reduction in the placebo group. Their cortisol dropped by 23%. The placebo group’s cortisol did not change significantly.
Scores on a broader measure of depression, anxiety, and stress fell by about 30% in the ashwagandha group versus 10% for placebo. These aren’t subtle differences, and they’re consistent across multiple trials. An international taskforce from the World Federation of Societies of Biological Psychiatry now provisionally recommends 300 to 600 mg of ashwagandha root extract daily for generalized anxiety disorder.
Sleep Quality Improvements
Ashwagandha helps you fall asleep faster and stay asleep longer. In an eight-week trial comparing ashwagandha (600 mg/day) to melatonin (3 mg/day) and placebo, ashwagandha reduced the time it took to fall asleep by about 14.6 minutes, while placebo only improved it by 7.2 minutes. For total sleep time, ashwagandha added roughly 36 minutes per night compared to about 29 minutes for placebo.
Melatonin performed slightly better on both measures (16.4 fewer minutes to fall asleep, 43.5 more minutes of total sleep), and combining the two produced the largest effect of all: 21 fewer minutes to fall asleep and 56 extra minutes of sleep per night. If you’re already taking melatonin and still struggling, adding ashwagandha may offer additional benefit.
Testosterone and Hormonal Effects
In aging, overweight men, ashwagandha supplementation produced a 14.7% greater increase in testosterone compared to placebo, along with an 18% greater increase in DHEA-S, a precursor hormone that supports testosterone production. A separate meta-analysis of four clinical trials found that ashwagandha increased sperm concentration, semen volume, and sperm motility in men with low sperm counts, alongside increases in testosterone and luteinizing hormone.
These are modest but real hormonal shifts. If you’re a young man with normal testosterone, don’t expect dramatic changes. The effect is more meaningful for men who are older, overweight, or dealing with subfertility.
Physical Performance and Endurance
A systematic review and meta-analysis found that ashwagandha significantly improved VO2 max (the maximum amount of oxygen your body can use during exercise) in healthy adults and athletes. The average improvement was about 3 mL/kg/min. To put that in perspective, that’s roughly the gain you’d expect from several weeks of consistent cardio training. The evidence was statistically significant but showed high variability between studies, meaning individual results will differ.
Memory and Focus
A placebo-controlled trial in stressed but otherwise healthy adults found that ashwagandha improved recall memory and sustained attention. Participants taking ashwagandha recalled patterns more accurately (scoring 12.9 vs. 10.1 on first-attempt memory tests) and made fewer total errors (17.5 vs. 27.7). Their sustained attention scores also improved compared to placebo. Reaction time, however, did not improve significantly more than placebo, so don’t expect it to sharpen your reflexes.
The cognitive benefits seem tied to ashwagandha’s stress-lowering effect. When cortisol stays chronically elevated, it impairs the brain areas responsible for memory and focus. Bringing cortisol down appears to let those systems function more effectively.
Dosage and Extract Types
Clinical trials have used doses ranging from 120 mg to 1,250 mg per day, but the benefits in most studies appeared greater at 500 to 600 mg daily. The dose that matters isn’t just the total milligrams of extract; it’s the withanolide content, the concentration of active compounds.
Different branded extracts standardize to very different withanolide levels:
- KSM-66: A root-only extract standardized to more than 5% withanolides, typically taken as 600 mg/day (two 300 mg capsules). This is the most widely studied extract.
- Shoden: A root and leaf extract standardized to 35% withanolide glycosides, used at much lower doses of 120 mg/day because it’s far more concentrated.
- Other extracts range from 1.5% to 5% withanolides, with daily doses between 250 and 600 mg.
Most clinical trials ran for 8 to 12 weeks. Some measured effects at interim checkpoints and found improvements building progressively, suggesting you should give it at least a couple of months before judging whether it’s working for you.
Thyroid Risks
Ashwagandha stimulates thyroid hormone production. Animal studies showed it increased circulating levels of the main thyroid hormone (T4) by as much as 111%. For people with an underactive thyroid, small studies suggest this could help normalize levels. But for people with normal or overactive thyroid function, this stimulation can push levels into a dangerous range.
Case reports have documented thyrotoxicosis (excess thyroid hormone) in people taking ashwagandha, with symptoms including rapid heartbeat, weight loss, and anxiety. One investigation found that some commercially available ashwagandha supplements actually contained amounts of thyroid hormones T3 and T4 that exceeded the doses used to treat hypothyroidism. If you have any thyroid condition, or take thyroid medication, this interaction is significant.
Liver Concerns and Other Side Effects
The NIH’s LiverTox database rates ashwagandha as a “likely cause of clinically apparent liver injury.” Liver problems typically appear 2 to 12 weeks after starting the supplement and usually present as jaundice (yellowing of the skin or eyes) and itching. Most cases are mild to moderate and resolve within 1 to 4 months of stopping the supplement.
However, rare fatal cases and emergency liver transplants have been reported, particularly in people with pre-existing liver disease or cirrhosis. Anyone with chronic liver conditions should avoid ashwagandha entirely.
There’s also a less obvious risk with long-term use: because ashwagandha suppresses cortisol production, chronic use can potentially lead to adrenal suppression, where your adrenal glands become underactive. The withanolides and alkaloids in ashwagandha may interfere with the genes encoding the enzymes your adrenals need to produce hormones. This is the same basic problem that happens when people take corticosteroid medications for too long and then stop abruptly. If you’ve been using ashwagandha daily for many months, tapering off rather than stopping suddenly is a reasonable precaution.