Ashwagandha

What is Ashwagandha?

Ashwagandha, Withania somnifera, is a small evergreen shrub in the nightshade family that grows across India, the Middle East and parts of Africa. Its root has been used in Ayurvedic medicine for around 3,000 years as a rasayana, or tonic. The Sanskrit name is usually translated as "smell of the horse", after the root's odour and the strength it was supposed to give. It is also sold as Indian ginseng or winter cherry, though it is not related to true ginseng.

The compounds most studied are withanolides, a group of steroid-like molecules, along with alkaloids and saponins. Supplements come in two broad kinds. Root powder is the dried, ground root, traditionally taken at several grams a day. Extracts concentrate the root, or root and leaf, and are standardised to a stated withanolide content. Most modern trials used a branded extract: KSM-66 (root only, about 5 per cent withanolides), Sensoril (root and leaf, at least 10 per cent) or Shoden (root and leaf, about 35 per cent withanolide glycosides). These are not interchangeable, and a result from one does not automatically apply to another or to plain powder.

It is marketed as an "adaptogen" — a substance said to help the body resist stress. That is a traditional and commercial term rather than a recognised pharmacological class.

How it works

How ashwagandha works in people is not settled. The leading idea is that it dampens the body's main stress system, the hypothalamic–pituitary–adrenal (HPA) axis, and so lowers cortisol. Several trials do report lower morning cortisol, which fits, but a fall in cortisol is a laboratory marker rather than proof that someone feels less stressed.

In animal and cell studies, withanolides and other constituents act on GABA receptors, the same calming system targeted by some sleep and anxiety medicines, which is a plausible route to the sleep effects. Other proposed actions — on inflammation, thyroid hormones and sex hormones — come mostly from animal work, with a few small human trials. The same breadth of activity is why regulators worry about side effects: something that shifts thyroid, blood sugar and reproductive hormones can do so in people who did not want it to.

What the research actually shows

Evidence strength varies by what is being claimed, so each use is graded separately against the published criteria rather than averaged into one reassuring letter.

Effective dosage

Most trials used 250 to 600 mg a day of a standardised root extract, taken once or split into two doses, for eight to twelve weeks. For stress, 300 to 600 mg a day did best in the 2022 meta-analysis; for sleep, the benefit was clearer at 600 mg a day or more. Many people take it in the evening, since drowsiness is a common effect, but no trial has shown that timing matters.

These doses refer to extracts. Root powder is far less concentrated, and traditional Ayurvedic use runs to several grams a day, so a milligram figure only means something when you know which form it is. Effects in trials built up over weeks rather than days.

Because long-term safety data run to only about three months, the cautious approach is to use it for a defined period and stop, rather than indefinitely.

Where products diverge from the research. The most common gap is not the dose but the form. A label that says "ashwagandha 500 mg" without naming an extract or a withanolide percentage may be plain root powder, which is not what the trials tested. Look for the extract name or the standardisation on the panel.

The second gap is combination. Ashwagandha turns up in sleep blends, "cortisol" formulas, testosterone boosters and gummies alongside magnesium, melatonin, rhodiola and caffeine, often in a proprietary blend that hides the amount. Someone taking two or three such products can end up above the studied range without realising it.

Extracts also differ. Root-only and root-plus-leaf extracts have different chemical profiles, and leaf falls outside traditional, root-only use. A trial on one branded extract is evidence for that extract.

Safety, side effects and interactions

In trials, ashwagandha has usually been well tolerated for up to about three months. The common side effects are mild: loose stools, nausea, stomach upset and drowsiness. Long-term safety has not been studied.

Liver injury is the most serious risk. The NIH LiverTox database rates ashwagandha a probable cause of clinically apparent liver injury. Cases typically appear 2 to 12 weeks after starting, with jaundice, itching, nausea and tiredness, and most resolve within a few months of stopping; rare severe cases have occurred, mainly in people with existing liver disease. Stop taking it and see a doctor if you notice yellowing of the skin or eyes, dark urine, pale stools, itching or pain in the upper right abdomen.

It can raise thyroid hormone levels, so avoid it with an overactive thyroid and check with your doctor if you take thyroid medicine. It may lower blood sugar and blood pressure, add to the effect of sedatives such as benzodiazepines and sleeping tablets, and stimulate the immune system, which matters for autoimmune disease and immune-suppressing medicines.

Do not take it if you are pregnant or breastfeeding: it has traditionally been linked to miscarriage and there are no safety data. Stop it two weeks before surgery. Avoid it with a hormone-sensitive prostate cancer, and if you are allergic to nightshades.

Regulators disagree. Denmark banned ashwagandha from food supplements in 2023 after its national food institute could not establish a safe level of intake. In the UK, the Food Standards Agency asked the Committee on Toxicity to assess its safety; the committee has noted possible effects on the thyroid, blood sugar and reproduction and liver case reports, and no safe level has been set while that work continues. In the US it is sold as a dietary supplement without pre-market approval.

None of this is medical advice. See the medical disclaimer for what that means before you act on anything here.