Best ashwagandha supplement: how to choose one and who should skip it
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- KSM-66 ashwagandha root extract, 600 mg. Best for: Adults who want a single daily capsule of a root extract used in trials. See options on Amazon
- Standardized ashwagandha extract, 300 mg. Best for: Adults who want to start at the low end of the studied range. See options on Amazon
- Root and leaf ashwagandha extract, 450 mg. Best for: Adults comfortable splitting doses through the day. See options on Amazon
- Ashwagandha with magnesium. Best for: People who also want magnesium in the same capsule. See options on Amazon
What ashwagandha is
Ashwagandha (Withania somnifera) is an evergreen shrub from parts of India, Africa and the Middle East, long used in Ayurvedic medicine. The National Center for Complementary and Integrative Health (NCCIH) says it contains compounds called withanolides, which have been associated with anti-inflammatory and antioxidant effects.
Supplements usually contain extracts of the root, the leaf, or both. They are promoted for stress and anxiety, sleep, male fertility and athletic performance.
What the research shows
Stress and anxiety. The NIH Office of Dietary Supplements (ODS) describes a 2021 review of seven trials with 491 adults in India. Ashwagandha (240 to 1,250 mg a day of extract for 6 to 8 weeks) significantly reduced stress and anxiety scores, sleeplessness, fatigue and cortisol compared with placebo. Benefits appeared greater at 500 to 600 mg a day than at lower doses.
Sleep. A small number of studies suggest ashwagandha extract may improve sleep quality, total sleep time and time to fall asleep, with larger effects in people with insomnia. NCCIH says some preparations may be effective for insomnia and stress, but evidence on anxiety is unclear.
Testosterone and fertility. NCCIH says limited evidence suggests 2 to 4 months of use may raise testosterone and sperm quality.
Everything else. NCCIH finds not enough evidence for asthma, athletic performance, cognitive function, diabetes, menopause or female infertility.
Many studies were small and used different preparations, so results from one branded extract may not apply to another.
Doses used in studies
| Source | Daily dose |
|---|---|
| Stress and anxiety review | 240 to 1,250 mg extract |
| Generalized anxiety (expert taskforce) | 300 to 600 mg root extract |
| Insomnia trial (KSM-66) | Two 300 mg capsules |
The 300 to 600 mg figure comes from an international taskforce of the World Federation of Societies of Biological Psychiatry and the Canadian Network for Mood and Anxiety Treatments, which provisionally recommended root extract standardized to 5% withanolides for generalized anxiety disorder in 2022, while noting more research is needed.
Safety: liver, thyroid and pregnancy
- Short term only. ODS says ashwagandha appears well tolerated for up to about 3 months; long-term safety is not known.
- Common side effects. Stomach upset, loose stools, nausea and drowsiness, usually mild.
- Liver injury. Rare, but reported. ODS describes five cases of people taking 450 to 1,350 mg a day who developed signs such as jaundice, itching, nausea and abdominal discomfort; they improved after stopping.
- Thyroid. Ashwagandha might affect thyroid hormone levels, and case reports describe thyrotoxicosis. It might interact with thyroid hormone medicines.
- Pregnancy and breastfeeding. NCCIH says to avoid it during pregnancy and not to use it while breastfeeding. Denmark banned ashwagandha in 2023, and France's food safety agency advised against it for certain groups in 2024.
- Other groups. NCCIH says it is not recommended before surgery or for people with autoimmune or thyroid disorders, and people with hormone-sensitive prostate cancer should avoid it.
- Medicines. NCCIH lists possible interactions with diabetes and blood pressure medicines, immunosuppressants, sedatives, anti-seizure drugs and thyroid hormones.
How to choose an ashwagandha supplement
- Extract, not just powder. Most trials used standardized extracts. Look for the extract amount in mg on the label.
- Plant part. Labels say root, or root and leaf. NOW Foods' KSM-66 product is root only; its 450 mg product is root and leaf.
- Withanolides. Standardized products list a minimum percentage, such as NOW Foods' 450 mg extract at minimum 2.4% total withanolides.
- Dose per capsule. NOW Foods' KSM-66 gives 600 mg in one capsule a day; its 450 mg product directs 1 capsule 2 to 3 times daily, so the daily total differs.
- Blends and gummies. Combination products and high mg gummies may not match studied extracts. Read the full ingredient list.
- Label cautions. NOW Foods labels its ashwagandha for adults only, not for pregnant or nursing women, with extra caution for thyroid and liver conditions.
What to look for when you buy
KSM-66 ashwagandha root extract, 600 mg
Best for: Adults who want a single daily capsule of a root extract used in trials
KSM-66 root extract appears in several trials NIH summarizes. NOW Foods' version gives 600 mg of organic root extract in one veg capsule a day.
Watch out: Use for no more than about 3 months without medical advice. Not for pregnancy, thyroid or liver conditions.
See options on AmazonStandardized ashwagandha extract, 300 mg
Best for: Adults who want to start at the low end of the studied range
300 mg sits at the bottom of the 300 to 600 mg range an expert taskforce provisionally recommended, so you can start low.
Watch out: Check the withanolide percentage and plant part. Stop if you notice stomach upset or signs of liver trouble.
See options on AmazonRoot and leaf ashwagandha extract, 450 mg
Best for: Adults comfortable splitting doses through the day
NOW Foods' 450 mg extract lists a minimum of 2.4% total withanolides and directs 1 capsule 2 to 3 times daily.
Watch out: Three capsules reaches 1,350 mg, the top of the doses in reported liver cases. Stay at the low end unless a clinician advises more.
See options on AmazonAshwagandha with magnesium
Best for: People who also want magnesium in the same capsule
Combination products pair ashwagandha with magnesium, which saves a second bottle if you already plan to take both.
Watch out: Check the ashwagandha amount, which may be lower than studied doses, and the magnesium form and amount.
See options on AmazonQuestions people ask
- What is the best ashwagandha supplement?
- For most adults, a standardized root extract at 300 to 600 mg a day, the range most used in studies. The best one for you also depends on your health conditions and medicines.
- When is the best time to take ashwagandha?
- Follow the label: some products are once daily and others split doses. Research has not set a best time of day, and drowsiness is a possible side effect, so notice how it affects you.
- How long can you take ashwagandha?
- NIH says it appears well tolerated for up to about 3 months. Long-term safety is not known.
- Who should not take ashwagandha?
- People who are pregnant or breastfeeding, have thyroid, autoimmune or liver conditions, have hormone-sensitive prostate cancer, are having surgery, or take thyroid, diabetes, blood pressure, immune or sedative medicines without a doctor's advice.
- Can ashwagandha damage the liver?
- It is rare, but cases of liver injury have been reported. Stop and see a doctor if you notice yellow skin or eyes, itching, nausea, unusual tiredness or abdominal discomfort.
Sources
- Ashwagandha: Usefulness and Safety (nccih.nih.gov), National Center for Complementary and Integrative Health
- Ashwagandha: Is it helpful for stress, anxiety, or sleep? Fact Sheet for Health Professionals (ods.od.nih.gov), NIH Office of Dietary Supplements
- KSM-66 Ashwagandha Veg Capsules (www.nowfoods.com/products/supplements/ksm-66-ashwagandha-veg-capsules), NOW Foods
- Ashwagandha 450 mg Veg Capsules (www.nowfoods.com/products/supplements/ashwagandha-450-mg-veg-capsules), NOW Foods