Ashwagandha root is the dried, ground root of a shrub called Withania somnifera, used for centuries in traditional Indian medicine and now one of the most popular herbal supplements worldwide. It belongs to the same plant family as tomatoes and peppers (Solanaceae) and grows natively across a wide belt from southern Europe through Africa to central China. Most of the interest in ashwagandha centers on its ability to lower cortisol, ease stress and anxiety, and improve sleep, and a growing number of placebo-controlled trials support those uses.
The Plant and Its Active Compounds
Ashwagandha is a small, woody shrub that thrives in subtropical climates. The root is the part most commonly harvested for supplements, though some products also include leaf extracts. Its name comes from Sanskrit and roughly translates to “smell of the horse,” a reference to both the root’s earthy odor and the traditional belief that it confers strength.
The root’s therapeutic effects come from three main classes of compounds. The most important are withanolides, a group of naturally occurring steroids that make up roughly 0.001% to 1.5% of the root’s dry weight. Withanolides drive the root’s anti-inflammatory and cell-protective activity. The root also contains alkaloids, which contribute antibacterial and anticancer properties, and flavonoids (about 43.5 mg per gram), which help neutralize free radicals and may support mood and blood sugar regulation. Together, these compounds give ashwagandha a broader pharmacological profile than most single-ingredient herbal supplements.
How It Affects Stress and Cortisol
Ashwagandha is classified as an “adaptogen,” meaning it helps the body manage stress more efficiently. Its withanolides and alkaloids appear to work on the hypothalamic-pituitary-adrenal (HPA) axis, the hormonal relay system that controls your cortisol output. They interact with receptors for cortisol and may also influence the enzymes your adrenal glands use to produce stress hormones, dialing down the overall stress signal. Separately, some of ashwagandha’s compounds promote calm by boosting the activity of GABA, a brain chemical that slows neural firing and has a sedative effect.
In a randomized, double-blind trial, adults who took ashwagandha for eight weeks showed significantly greater reductions in morning cortisol levels compared to a placebo group. They also scored lower on a standard clinical anxiety scale (the HAM-A). These weren’t dramatic, overnight changes, but they were statistically meaningful and consistent with what other trials have found.
Effects on Sleep
Sleep improvement is one of ashwagandha’s better-supported benefits. In a six-week trial of 150 adults with self-reported sleep problems, 72% of those taking ashwagandha reported better sleep quality, compared with 29% in the placebo group. A separate eight-week study using the KSM-66 root extract found improvements in how quickly participants fell asleep, overall sleep quality, and how alert they felt in the morning.
A 2021 meta-analysis pooling data from five trials (372 adults total) confirmed these patterns and noted that the benefits were most pronounced at a dose of 600 mg per day taken for at least eight weeks. Lower doses and shorter durations still showed some effect, but the signal was weaker.
Testosterone and Physical Performance
Ashwagandha has measurable hormonal effects beyond cortisol. In a crossover study of overweight men, eight weeks of supplementation produced a 14.7% increase in testosterone and an 18% increase in DHEA-S (a precursor hormone that supports energy and immune function) compared to placebo. Cortisol and estradiol trended downward as well, though those drops didn’t reach statistical significance. Other research has linked ashwagandha to faster exercise recovery in people doing resistance training, though large-scale performance data is still limited.
How Long Before You Notice Results
Clinical trials have measured benefits at time points ranging from 30 days to 90 days. Some of the shortest trials, lasting just four weeks, found that participants reported reduced stress, improved mood, better energy, and a greater sense of calm. For sleep specifically, six weeks appears to be a reasonable minimum, with the strongest results appearing at eight weeks or longer. If you’ve been taking ashwagandha for two to three months without noticing any change, it’s reasonable to conclude it may not be effective for you.
Common Forms and Doses
Ashwagandha supplements come in several forms, and they’re not all equivalent. You’ll see raw root powder, concentrated root extracts, and blends that include both root and leaf material. The most widely studied branded extracts include KSM-66 (a root-only extract), Sensoril (root and leaf), and Shoden (root and leaf). Each uses a different extraction process and delivers a different concentration of withanolides, so switching between brands may change your experience.
Doses used in clinical research typically range from 225 mg to 600 mg per day of a concentrated extract. The meta-analysis on sleep found 600 mg daily to be the most effective dose studied. Raw root powder is less concentrated, so doses tend to be higher, often in the range of 1,000 to 3,000 mg daily. Capsules, gummies, and powders are all common delivery methods, and none has a clear advantage over another as long as the active compound concentration is comparable.
Who Should Avoid It
Ashwagandha is generally well tolerated in the short term, but it’s not appropriate for everyone. The National Center for Complementary and Integrative Health identifies several groups who should avoid it:
- Pregnant or breastfeeding women: Ashwagandha should not be used during pregnancy or while nursing.
- People with thyroid disorders: Ashwagandha can alter thyroid hormone levels, making it risky for anyone with hyperthyroidism, hypothyroidism, or Hashimoto’s disease.
- Autoimmune conditions: Because ashwagandha stimulates immune activity, it may worsen conditions like lupus, rheumatoid arthritis, or multiple sclerosis.
- Hormone-sensitive prostate cancer: The testosterone-boosting effect makes ashwagandha a concern for this group.
- People scheduled for surgery: Its sedative and blood-pressure-lowering properties could interfere with anesthesia.
Ashwagandha also has the potential to interact with several medication classes, including drugs for diabetes, high blood pressure, seizures, and thyroid conditions, as well as immunosuppressants and sedatives. The interaction risk comes from ashwagandha amplifying or competing with the same biological pathways these drugs target. If you take any of these medications, it’s worth discussing ashwagandha with your prescriber before starting it.
One less-discussed concern: because ashwagandha actively suppresses cortisol production, long-term continuous use could theoretically lead to HPA axis suppression, where your adrenal glands become less responsive on their own. Some clinicians recommend cycling ashwagandha (for example, taking it for two to three months and then pausing) rather than using it indefinitely, though formal guidelines on cycling don’t yet exist.