Ashwagandha is a shrub whose root has been used in Indian traditional medicine for centuries. As a modern supplement it is sold as an adaptogen, a term with no agreed definition that usually means "helps with stress", and the trials have mostly tested it for stress, anxiety, sleep and, in men, strength and testosterone.

Two things make this entry harder to read than most. The trials are small, short and largely funded by the companies that make the branded extracts they test, and their results are unusually large for a herbal product, which is either good news or a warning. And the safety literature has grown in a direction the marketing has not caught up with.

The root contains withanolides, a family of steroidal compounds, and the branded extracts are standardized to a withanolide content. The proposed stress mechanism is damping of the hypothalamic-pituitary-adrenal axis, the system that produces cortisol, and trials have measured lower morning cortisol on ashwagandha. Effects on GABA signaling are proposed for sleep and anxiety.

For strength and testosterone, the proposals run through the same stress pathway and through direct hormonal effects, with one trial reporting raised testosterone in men. None of this has been traced from a specific compound to a specific receptor in the way the peptide guides on this site describe.

Anxiety and stress: large effects, low certainty. A 2022 meta-analysis of 12 randomized trials in 1,002 adults found ashwagandha reduced anxiety and stress scores by large standardized amounts compared with placebo. The between-trial heterogeneity was extreme, over 90%, and the authors rated the certainty of evidence low for both outcomes. A 2019 trial in 60 stressed adults, representative of the better ones, found a significant reduction on one anxiety scale, a non-significant one on another, and lower morning cortisol, with no adverse events reported.

Sleep. A 2021 meta-analysis of five trials in 400 adults found a small to moderate improvement in sleep, larger in people with diagnosed insomnia and in trials of eight weeks or more.

Strength and testosterone: one trial. A 2015 trial in 57 untrained young men found larger strength gains, more muscle growth, lower body fat and a larger rise in testosterone over eight weeks of training on ashwagandha than on placebo. It has been widely cited and not independently replicated at that scale.

What to make of it. The pattern, large effects in small industry-funded trials with high heterogeneity, is the pattern that tends to shrink when larger independent trials are run. That has not happened yet, so the honest grade is early.

The trials report ashwagandha as well tolerated, with drowsiness and stomach upset the common complaints. The case literature says something the trials did not capture. A 2020 case series from Iceland and the US Drug-Induced Liver Injury Network described five people with jaundice and liver injury after two to twelve weeks of ashwagandha, resolving over one to five months. A 2023 series from India reported eight cases of single-ingredient ashwagandha liver injury, three of them in people with pre-existing liver disease who developed acute-on-chronic liver failure and died. A 2026 scoping review counted 25 published cases worldwide, including one liver transplant and three deaths, and concluded that a reproducible syndrome exists and that people with advanced liver disease should avoid it.

The absolute risk is unknown, because nobody knows how many people take it. What is known is that the injury is idiosyncratic, cholestatic, arrives after weeks, and is worst in people whose liver was already compromised. Ashwagandha also affects thyroid hormone levels and is not advised in pregnancy.

Ashwagandha is sold as a dietary supplement in the United States and most of the European Union without review of its claims. Denmark banned its sale in 2023 on the basis of a safety assessment citing effects on thyroid and sex hormones and the liver. Several other countries have issued warnings or restricted it in pregnancy.

That is an unusual trajectory for a supplement: the evidence of harm has moved regulators before the evidence of benefit has moved anyone. A reader should weigh the fact that one European country has concluded it should not be sold at all.