Ashwagandha: the evidence, and the reasons for care

Withania somnifera, known as ashwagandha, is a root used in classical Ayurveda as a rasayana — a category of preparations associated with vitality and rejuvenation.

It has attracted substantial research interest and it is among the Ayurvedic botanicals with the most clinical trial data. It also has specific safety considerations that are frequently omitted from popular coverage.

What the trials show

Stress and anxiety. The most-studied application. Multiple randomised placebo-controlled trials have reported reductions in perceived stress scores and anxiety measures, and several meta-analyses have found a benefit.

The caveats are substantial. Trials are generally small, of short duration — typically eight to twelve weeks — and a large proportion originate from a limited number of centres. Many are funded by manufacturers of the specific extract tested. Reviews have noted risk of bias and heterogeneity, and have generally described the evidence as promising rather than conclusive.

Sleep. Several trials report improvements in sleep quality measures, mostly using subjective scales. Some studies include objective measures with more modest results. Reviews have described a small to moderate benefit with similar quality limitations.

Physical performance. A number of trials in resistance training report improvements in strength and body composition measures. Effect sizes vary considerably, sample sizes are small, and the picture is less consistent than for stress.

Testosterone and fertility. Studies in men, some in infertile populations, report changes in hormonal parameters. Findings are heterogeneous and the populations studied differ substantially, which limits generalisation.

Thyroid. Some evidence suggests ashwagandha may increase thyroid hormone levels. This is a reason for caution rather than an established benefit, and it is directly relevant to safety.

The safety issues, which are the important part

Liver injury. This is the most serious documented concern. Cases of hepatotoxicity associated with ashwagandha supplements have been published, and national medicines regulators in several countries have issued warnings. Some cases were serious.

Anyone with existing liver disease should not take it without medical advice, and anyone taking it who develops symptoms of liver problems — jaundice, dark urine, marked fatigue, right upper abdominal pain, nausea — should stop and seek medical assessment.

Thyroid effects. Because it may raise thyroid hormone levels, it should be avoided or used only under medical supervision by anyone with hyperthyroidism, and anyone on thyroid medication should discuss it with their prescriber, since dose adjustment may become necessary.

Autoimmune conditions. Because of proposed immune-stimulating effects, caution is generally advised in autoimmune disease. The evidence for actual harm is limited; the caution is precautionary.

Pregnancy. Traditional sources and modern advice both counsel avoidance in pregnancy. Do not take it if pregnant or trying to conceive without medical advice.

Sedative and immunosuppressant interactions. Potential additive effects with sedatives, and theoretical interaction with immunosuppressant medication.

Product quality. Supplements vary enormously in extract type, standardisation and dose. Contamination and adulteration have been documented across the herbal supplement industry generally. Third-party testing is worth looking for.

Doses used in research

Trials have generally used standardised root extracts, most commonly in the range of a few hundred milligrams a day, taken for eight to twelve weeks.

Long-term safety beyond the trial durations is not well characterised. This is a general limitation across the supplement field and it applies here.

Extracts differ. A trial of one standardised extract does not establish anything about a different product, and doses of crude powder are not equivalent to doses of concentrated extract.

What is reasonable to conclude

The evidence for a modest effect on perceived stress and sleep quality is among the better bodies of evidence for any Ayurvedic botanical, and it is not strong enough to be described as established.

The safety profile is not benign, and the liver injury signal in particular means this is not a supplement to take casually or indefinitely without thought.

Anyone considering it should discuss it with a doctor, particularly if they have thyroid disease, liver disease, an autoimmune condition, are pregnant, or take any prescribed medication.

This article summarises published research. It is not a recommendation to take any supplement. Ashwagandha has been associated with liver injury; do not use it if you have liver disease, and stop and seek medical advice if you develop jaundice, dark urine or unexplained fatigue.