Ashwagandha: Benefits, Side Effects and Evidence

Short answer: Ashwagandha is an Ayurvedic herb sold mainly as a supplement for stress and sleep. Small, short trials suggest some ashwagandha extracts may lower perceived stress and modestly improve sleep, particularly in people with insomnia. [S01] [S03] [S04] The evidence is limited: most studies were small, many were done in India, and they tested different products and doses. [S01] [S02] It appears to be well tolerated for up to about three months, but rare liver injury, possible thyroid effects and drug interactions mean it is not for everyone. [S01] [S02] [S07]

This guide covers what the research shows for each common use, the doses that were tested, the side effects and who should skip it.

What ashwagandha is

Ashwagandha (Withania somnifera) is an evergreen shrub grown in parts of Asia, Africa and Europe. Its root has long been used in Ayurvedic and Unani medicine, and it is sometimes called winter cherry or Indian ginseng, although it is not related to ginseng. [S01]

The plant contains compounds called withanolides, which are thought to explain many of its proposed effects, though lab research suggests other components may be involved too. [S01] Supplements are made from the root, the leaf or both, and are often standardized to a specific withanolide content. That variety matters, because the products tested in studies are not interchangeable. [S01] [S02]

Does ashwagandha help with stress?

This is the most-studied use, and the results lean positive but come with real caveats.

A 2021 review cited by the NIH Office of Dietary Supplements (ODS) identified seven studies of 491 adults in India with high stress or diagnosed anxiety disorders. Over six to eight weeks, those taking ashwagandha reported less stress than those taking a placebo. [S01] Most trials published since then point the same way, but not all of them: in one 12-week trial of 120 adults with fatigue, an ashwagandha root extract did not reduce perceived stress, though it did reduce fatigue. [S01]

Meta-analyses that pool these trials find benefits, but they also find a lot of disagreement between studies:

• A 2022 analysis of 12 papers with 1,002 participants found lower stress and anxiety scores with ashwagandha, but rated the certainty of the evidence as low for both. [S04]
• A 2024 analysis of nine trials with 558 patients found lower scores on a standard stress scale, a standard anxiety scale and blood cortisol compared with placebo. [S05]

Some studies measured cortisol, the main stress hormone, and found it fell. [S05] That fits with the stress results, but a single cortisol reading says little about how a person feels day to day.

Does it help with anxiety?

Here the picture is less settled. Some pooled analyses report lower anxiety scores, [S04] [S06] but NCCIH describes the evidence for anxiety as unclear. [S02] A 2024 review of five trials with 254 people found a large drop on the Hamilton Anxiety Scale, yet the results varied so much from study to study that the authors called for larger trials before drawing firm conclusions. [S06]

An international task force from the World Federation of Societies of Biological Psychiatry and the Canadian Network for Mood and Anxiety Treatments issued a provisional recommendation in 2022 for 300 to 600 mg a day of a root extract standardized to 5% withanolides for generalized anxiety disorder. The task force said it could not make a stronger recommendation without more data. [S01]

Ashwagandha is not a substitute for diagnosis and treatment of an anxiety disorder.

Does ashwagandha help you sleep?

There is modest support for sleep. A 2021 meta-analysis of five randomized trials with 400 participants found a small but significant improvement in overall sleep. Effects were larger in people diagnosed with insomnia, at doses of 600 mg a day or more, and in studies that lasted at least eight weeks. [S03] Participants also reported feeling more alert on waking. [S03]

A 2024 review found improvements in how long it took to fall asleep, total sleep time and sleep quality scores, but not in time spent awake after first falling asleep. [S06] NCCIH says some ashwagandha preparations may be helpful for insomnia. [S02]

If sleep is your main concern, see our guide to magnesium for sleep for another commonly studied supplement.

Testosterone and other claims

NCCIH says limited evidence suggests that taking ashwagandha for two to four months may increase testosterone levels and sperm quality. [S02] Beyond stress, sleep and testosterone, NCCIH says there is not enough evidence to know whether ashwagandha helps other conditions. [S02]

Doses used in studies

There is no official recommended dose. The trials summarized by ODS used a wide range of products, including:

• 250 to 600 mg a day of a root extract in most sleep studies [S01]
• 240 to 1,250 mg a day of various extracts in stress and anxiety studies [S01]
• 120 mg a day of a root-and-leaf extract in one sleep study [S01]

In a 2022 dose-response analysis, the stress benefit appeared at 300 to 600 mg a day. [S04] Because extracts differ in plant part, solvent and withanolide content, a dose from one study does not translate directly to a different product. [S01] [S02]

Side effects

ODS says ashwagandha appears to be well tolerated for up to about three months, but its long-term safety is not known. [S01] The most common side effects are usually mild:

• Drowsiness
• Upset stomach, loose stools or diarrhea
• Nausea or vomiting [S01] [S02]

In the 2024 stress and anxiety analysis, four of nine trials reported mild to moderate side effects. [S05]

Liver injury

Liver injury is rare, but it has been reported. [S02] In a case series of five patients from Iceland and the U.S. Drug-Induced Liver Injury Network, all developed jaundice, with symptoms such as nausea, tiredness and itching, two to 12 weeks after starting ashwagandha. None had liver failure, and liver tests returned to normal within one to five months in the four patients who were followed. Lab analysis confirmed ashwagandha in the supplements; four of the patients were also taking other supplements. [S07]

Thyroid effects

Ashwagandha might affect the thyroid. In small studies it raised thyroid hormone levels, and three case reports describe an overactive thyroid (thyrotoxicosis) in women taking it, which resolved when they stopped. [S01] This is why it may interact with thyroid hormone medicines. [S01] [S02]

Drug interactions

According to NCCIH and ODS, ashwagandha might interact with:

• Diabetes medicines
• Blood pressure medicines
• Immunosuppressants
• Sedatives
• Anti-seizure medicines (anticonvulsants)
• Thyroid hormone medicines [S01] [S02]

Our guide to herb-drug interactions explains how supplements can change the way medicines work and what to bring up with a pharmacist.

Who should avoid ashwagandha

NCCIH and ODS flag several groups:

• Pregnant or breastfeeding people. Some reports suggested it could cause miscarriage. Denmark banned ashwagandha in 2023, and a French food safety agency advised against it in pregnancy and breastfeeding in 2024. The American Herbal Pharmacopoeia, one source behind the concern, says its report was misrepresented and that there is no evidence the root causes abortions. [S01] [S02]
• Men with hormone-sensitive prostate cancer, because ashwagandha may raise testosterone. [S01] [S02]
• People with thyroid or autoimmune disorders, and people about to have surgery. [S02]
• People taking the medicines listed above, unless their clinician approves. [S01] [S02]

How strong is the evidence?

Product quality

Like other supplements, ashwagandha products do not need approval from the Food and Drug Administration (FDA) before they are sold. [S02] Products also differ in which part of the plant they use and how they are standardized. [S01] For a closer look at another popular supplement, see our review of berberine.