Ashwagandha and the Brain: What the Evidence Shows (and the Liver-Safety Question)

By Peter Benson, Cognitive Enhancement Researcher  ·  Updated October 2026  ·  Citations re-verified

Short answer: Ashwagandha’s best evidence is for stress: several small trials found standardised root extract lowered perceived stress and cortisol over six to eight weeks. Effects on sleep are small, and on cognition preliminary. It’s usually well tolerated in short trials, but it’s a likely cause of rare liver injury.

Ashwagandha is one of the best-selling supplements of the last decade, marketed for stress, sleep, energy and much more. Unlike many trendy supplements, it has a reasonable body of evidence behind its main claim, stress. But the trials are small and short, much of the research is funded by extract makers, and there’s a genuine safety signal for the liver that marketing tends to skip.

This ashwagandha guide covers how it’s thought to work, the evidence for stress, anxiety, sleep and cognition, the liver question, other cautions and regulatory concerns, and what to look for in a product. It sits in the Nootropics & Supplements hub.

What is ashwagandha and how might it work?

Ashwagandha (Withania somnifera) is a shrub used in Ayurvedic medicine, often called an adaptogen: something thought to help the body cope with stress. Its main active compounds are withanolides, which is why extracts are standardised to a withanolide percentage. Most trials use root extracts; some products also use leaf, which is more concentrated in some withanolides and has been the subject of separate safety concerns.

One proposed explanation is that ashwagandha influences the hypothalamic-pituitary-adrenal (HPA) axis, which helps regulate the stress response. Some human trials have reported lower cortisol, but that doesn’t establish exactly how ashwagandha produces its effects. Other proposed mechanisms, such as effects on GABA-related signalling, rest mainly on preliminary research. For context on the stress system itself, see chronic stress and cortisol.

Does ashwagandha reduce stress and anxiety?

Probably, modestly. In a widely cited trial, 64 stressed adults took 300mg of a standardised root extract (KSM-66) twice a day or placebo for 60 days. The ashwagandha group had larger falls in stress and anxiety scores and in blood cortisol, with side effects similar to placebo (Chandrasekhar et al., 2012).

It isn’t a one-off: NIH’s Office of Dietary Supplements summarises several studies in which people taking ashwagandha for six to eight weeks reported less stress and anxiety and had lower stress-hormone levels, with some finding 500–600mg a day more effective than lower doses (NIH ODS). But it describes the evidence as limited and varied, and concludes only that ashwagandha “might help reduce stress and anxiety.” It isn’t a substitute for treatment of an anxiety disorder.

Does ashwagandha help with sleep?

A little. A meta-analysis of five placebo-controlled trials (about 400 people, all in India) found a small improvement in overall sleep, rated moderate certainty. Subgroup analyses suggested larger effects in people with insomnia, with eight weeks or more of use, and with some higher-dose regimens (600mg a day or more) (Cheah et al., 2021). Subgroup comparisons like these don’t establish that 600mg is an optimal or universally effective dose. One of those trials, in 60 adults with insomnia and anxiety, used 300mg twice a day for eight weeks (Langade et al., 2019). NIH ODS calls the overall sleep benefits small (NIH ODS). For the wider picture, see sleep and recovery.

Does ashwagandha improve cognition?

The evidence is preliminary. Some small trials in stressed adults report improvements on memory or attention tests, but it’s unclear how much is a direct effect and how much follows from being less stressed and sleeping better. On current evidence, ashwagandha is best thought of as a stress-and-sleep supplement that might indirectly help thinking, not a nootropic to take for focus. See what to expect from nootropics.

How strong is the ashwagandha evidence?

Reasonable for a supplement, but with familiar limits. Most trials are small, last six to twelve weeks, are run in India, and many are funded by companies that make branded extracts. That doesn’t make the results worthless, but effect sizes may be flattering, and long-term effects are largely unstudied. NIH ODS notes that no safety concerns appeared in studies lasting up to about three months, but that it isn’t clear whether longer use is safe.

Newer systematic reviews pool more trials and generally report favourable results for perceived stress and anxiety-related symptoms. A 2026 dose-response meta-analysis in Complementary Therapies in Medicine included 22 randomised trials and 1,391 adults (Complementary Therapies in Medicine, 2026). But differences in extracts, doses, participants and study quality limit how confidently pooled results apply to everyday users. The newer evidence strengthens the case for a possible benefit; it doesn’t establish an optimal dose, long-term safety, or effectiveness as a treatment for anxiety or depression.

Is ashwagandha safe for your liver?

For most people in short trials, no liver problems have been reported. But in real-world use, ashwagandha has been linked to rare cases of liver injury. A case series from Iceland and the US Drug-Induced Liver Injury Network described five patients who developed jaundice after taking ashwagandha products (Björnsson et al., 2020). NIH LiverTox now rates ashwagandha a “likely cause” of clinically apparent liver injury (NIH LiverTox).

According to LiverTox, the injury usually appears 2 to 12 weeks after starting, typically with jaundice and itching. Most cases are mild to moderate and resolve within one to four months of stopping, but fatal liver failure has been reported, mainly in people with existing liver disease or cirrhosis. LiverTox advises against taking it again after a reaction. The reactions appear rare and unpredictable; whether product quality plays a part in some cases isn’t known.

Practically: avoid ashwagandha if you have liver disease, buy a tested product, don’t combine it carelessly with heavy alcohol or other substances known to stress the liver, and stop and seek medical advice promptly if you notice yellowing of the skin or eyes, dark urine, itching, unusual tiredness, nausea or upper-right abdominal pain. See are nootropics safe?.

Who else should be cautious?

Thyroid. Ashwagandha may affect thyroid function and could interact with thyroid medicines (NIH ODS). Use it only with medical advice if you have a thyroid condition.

Pregnancy, breastfeeding and prostate cancer. NIH ODS says it may not be safe in these groups.

Medicines. It may interact with diabetes and blood-pressure medicines, sedatives, and drugs that suppress the immune system (NIH ODS). Common side effects are usually mild: upset stomach, loose stools, nausea and drowsiness. If you have an autoimmune condition or surgery planned, ask your doctor first.

Regulators. Denmark banned ashwagandha in food supplements in 2023, after a Danish government-commissioned report found insufficient evidence to set a safe intake level. The Netherlands’ public-health institute advised against its use in 2024, and the UK Food Standards Agency has called for evidence on whether restrictions are needed (NutraIngredients, 2026). Industry groups dispute these assessments, and there’s no EU-wide ban, but they’re a sign that regulators consider the safety evidence incomplete.

Ashwagandha claims ranked by evidence

🟢 Stronger or replicated evidence  ·  🟡 Limited, mixed or preliminary evidence  ·  🔴 Not established or not supported

What dose did the trials use?

Most stress and sleep trials used a standardised root extract at 250–600mg a day, often 300mg twice a day, for six to twelve weeks. No optimal dose has been established. Many used the branded root extract KSM-66, standardised to about 5% withanolides, but extracts differ, so a dose of one isn’t equivalent to another. These are research references, not recommendations; effects, if any, build over weeks rather than hours.

Buying ashwagandha: what to check

Look for a root extract with the withanolide percentage and amount per serving stated, independent testing, and no leaf if you want to match most trials. Avoid unstandardised powders of unknown strength.

Root-only extracts are more directly comparable with many published trials, but that doesn’t mean they’re free of liver-injury risk. Independent testing can help confirm identity, composition and the absence of contaminants; it can’t guarantee that you won’t react to the herb itself.

This is an affiliate link. If you buy through it, NeuroEdge Formula may earn a commission at no extra cost to you. For a different adaptogen with a different evidence base, see Rhodiola.

Frequently asked questions

Scientific references