Ashwagandha is an herbal supplement derived from the root of a shrub in the nightshade family, native to India and parts of Africa. It has been used for centuries in Ayurvedic medicine as a general tonic for vitality and stress resilience, and modern clinical trials have begun to validate several of those traditional uses, particularly for reducing cortisol, easing anxiety, and improving sleep.
The Plant and Its Active Compounds
The plant’s scientific name is Withania somnifera, and it’s sometimes called Indian ginseng or Indian winter cherry. While the leaves, flowers, and seeds all have traditional uses, the root is the part most commonly found in supplements. It’s typically sold as a fine powder (mixed into water, milk, or honey) or as a concentrated capsule extract.
Researchers have identified over 50 biologically active substances in ashwagandha, including alkaloids, flavonoids, and a class of compounds called withanolides. Withanolides are the primary drivers behind most of the herb’s medicinal effects. They appear to influence the body’s stress-response system and have both immune-stimulating and antioxidant properties. Most standardized supplements list their withanolide content as a percentage, typically ranging from about 5% to 35% depending on the extract.
How It Affects Stress and Cortisol
The best-studied benefit of ashwagandha is stress reduction, and the mechanism centers on something called the HPA axis, which is the communication loop between your brain and adrenal glands that controls cortisol release. Ashwagandha appears to dial down the activity of this system, lowering the amount of cortisol your body produces under stress.
In a 60-day randomized, double-blind trial of 60 mildly anxious but otherwise healthy adults, those taking 240 mg of ashwagandha extract daily experienced a 23% reduction in fasting morning cortisol levels. The placebo group saw essentially no change (a 0.5% increase). Multiple reviews of clinical trials have consistently found that ashwagandha significantly reduces both subjective stress and anxiety ratings, along with measurable drops in cortisol, when compared with placebo.
Effects on Sleep
Ashwagandha also shows promise for sleep. Systematic reviews of the clinical data report that it shortens the time it takes to fall asleep, increases total sleep duration, and improves self-reported sleep quality. One randomized trial found that after 10 weeks, participants taking ashwagandha fell asleep in about 29 minutes on average compared to roughly 34 minutes for the placebo group. A pilot study reported even more dramatic subjective improvements: around 92% of participants noted better sleep quality and 89% reported improved mood upon waking. These aren’t transformative numbers for people with severe insomnia, but for mild sleep difficulties tied to stress, the evidence is encouraging.
Testosterone and Exercise Performance
For men interested in fitness, ashwagandha has some intriguing data. Supplementation has been associated with roughly a 15% increase in testosterone levels. In an 8-week trial of resistance-trained men, those taking 300 mg of root extract twice daily saw notably greater gains in bench press strength (averaging 46 kg versus 26.4 kg in the placebo group) along with measurable increases in arm muscle size. The combination of higher testosterone and lower cortisol likely creates a more favorable hormonal environment for building muscle and recovering from training.
Thyroid Activity: A Benefit and a Risk
Ashwagandha stimulates the thyroid gland. Animal research shows it can increase circulating levels of the thyroid hormone T4 by as much as 111%. Small clinical trials have found it can help normalize thyroid levels in people with an underactive thyroid, which sounds like a clear benefit.
The problem is that this same thyroid-stimulating effect can push people into dangerous territory. A case report describes a 73-year-old woman who developed a rapid heart rhythm and suppressed TSH levels (an early marker of an overactive thyroid) after two years of taking ashwagandha for her hypothyroidism. Some commercially available ashwagandha supplements have even been found to contain amounts of thyroid hormones T3 and T4 that exceed standard treatment doses for hypothyroidism. If you have any thyroid condition, or you’re taking thyroid medication, this is a supplement to approach with real caution.
Liver Safety Concerns
A pattern of liver injury associated with ashwagandha has emerged in recent years. A case series from India documented 23 patients with ashwagandha-related liver injury between 2019 and 2022, 8 of whom were taking single-ingredient ashwagandha products. The most common presentation was cholestatic hepatitis, a form of liver inflammation that disrupts bile flow. In most patients without preexisting liver disease, the injury was prolonged but eventually resolved on its own after stopping the supplement.
The serious concern is for people with underlying liver problems. Three patients in the series who already had chronic liver disease developed acute-on-chronic liver failure, and all three died. One additional patient from prior case reports required a liver transplant. These are rare outcomes relative to the millions of people taking ashwagandha worldwide, but they establish that liver toxicity is a real, if uncommon, risk. Heavy alcohol use or existing liver conditions raise the stakes considerably.
Typical Dosing and What to Expect
Clinical trials have used a wide range of doses. Concentrated root extracts (the most common supplement form) typically range from 240 mg to 600 mg per day, with some studies using up to 1,000 mg. Traditional powdered root preparations use higher amounts because they’re less concentrated. Most positive results in trials appear within 6 to 10 weeks of consistent daily use, so this isn’t something that produces noticeable effects overnight.
The two most widely available branded extracts are KSM-66, made from roots only, and Sensoril, which uses both roots and leaves. Both have been used in clinical research with positive results. When choosing a product, the withanolide percentage on the label gives you the best indication of potency.
Who Should Be Careful
Beyond thyroid conditions and liver disease, ashwagandha belongs to the nightshade family (alongside tomatoes and peppers), so people with nightshade sensitivities may react to it. Because it can lower cortisol and affect hormonal balance, it has the potential to interact with medications for thyroid disorders, diabetes, blood pressure, and immunosuppression. Pregnant women have traditionally been advised to avoid it. The most commonly reported mild side effects in trials are gastrointestinal: nausea, loose stools, and stomach discomfort, usually at higher doses.