SubEx

Herb

Ashwagandha

An Ayurvedic root sold as an adaptogen. Trials find cortisol and anxiety falling; the testosterone claim is the one that did not hold.

Findings
5
Best evidence
★★★
Open questions
3

At a glance

Myth check

Ashwagandha is widely marketed as a natural testosterone and libido booster for men, often advertised alongside its stress-relief claims.

In the trial that measured it (Lopresti et al. 2019), testosterone did rise over 60 days in men taking ashwagandha, but not significantly more than in the placebo group (p=.158). In the same trial, the cortisol- and anxiety-lowering effects were statistically significant.

The popular 'testosterone booster' framing outruns the trial data: in the one trial that measured it, ashwagandha's cortisol and anxiety effects were significant but its effect on testosterone was not — the gap between marketing and evidence sits specifically on that outcome, not on stress or cortisol.

The findingsStrongest first
1↓
Mood & wellbeingIn nine cortisol studies, ashwagandha was taken daily for weeks

All nine studies in one cortisol review had people take ashwagandha daily, in studies lasting 30 to 112 days. None tested what one dose does.

★★★Well replicated — this finding’s sources average out to meta-analyses, systematic reviews or high-powered trials.The review gives each study's cortisol only at the end of its course, so how soon any fall begins is unknown. The falls it reports are measured against where people started, not against placebo, and one of the nine had no placebo group. The two studies that measured cortisol in saliva disagreed, and one found no change. Extract and dose differ from study to study, from 60 mg to 5 g a day.Click to keep this openManage stress and anxiety
2↓
Mood & wellbeingAshwagandha lowered cortisol and stress in highly stressed adults

Across nine trials in 558 people, pooled in one review, cortisol fell against placebo, and so did self-rated stress and anxiety. The people studied were already highly stressed when they started.

★★★Well replicated — this finding’s sources average out to meta-analyses, systematic reviews or high-powered trials.The trials recruited adults who already described themselves as highly stressed, so the same fall may not appear in someone whose cortisol starts out ordinary. Four of the nine trials reported mild-to-moderate side effects. Extract and dose differed from trial to trial, so the pooled result describes no one product. The second review's two studies that measured cortisol in saliva rather than blood disagreed, one finding no change at all. In a later 12-week trial of older, overweight adults, stress scores fell about as far on placebo as on ashwagandha, and cortisol was not measured, so the self-rated stress part of this result is less settled than the cortisol part.Click to keep this openManage stress and anxiety
3?
OtherNobody has watched ashwagandha's cortisol drop past 16 weeks

The trials ran 16 weeks at most and reported no serious side effects. Past that nothing has been measured, and the review that gathered them asks for medical supervision past the short term.

★☆☆Contested — the evidence disagrees with itself, or the finding carries a caution. A caution or conflict always shows one star, however strong the sources are.CautionThis is a gap in what has been measured, not a recorded harm: no trial reported an adrenal problem, because none of them looked for one. Inside their 30-to-112-day windows the trials reported no serious side effects.Click to keep this openManage stress and anxiety
4↓
Mood & wellbeingAshwagandha eases stress in 22 pooled trials; by how much is unclear

The broadest pooling found stress, anxiety and depression scores falling on ashwagandha, and more at higher doses. The size it reports is several times what earlier trials found.

★☆☆Contested — the evidence disagrees with itself, or the finding carries a caution. A caution or conflict always shows one star, however strong the sources are.Conflicting evidenceA pooled stress effect of nearly six standard deviations would mean almost nobody on placebo scored as low as anyone on ashwagandha, while earlier trials of the herb measured effects of 0.63 to 0.74 standard deviations. The authors themselves note the trials differed widely, and pooling very different trials can produce a size no single trial supports. The dose-response finding is read off the same pooling.Click to keep this openManage stress and anxiety
5↕
Mood & wellbeingAshwagandha did not beat placebo for stress in one 12-week trial

Over 12 weeks in 120 overweight adults aged 40 to 75, stress scores fell about as far on placebo as on ashwagandha. Fatigue fell further on ashwagandha than on placebo.

★☆☆Contested — the evidence disagrees with itself, or the finding carries a caution. A caution or conflict always shows one star, however strong the sources are.Conflicting evidencePlacebo groups in earlier ashwagandha stress trials barely moved, falling around 5.5%, so a 36% placebo fall may be what hid the difference here rather than a weaker herb. Cortisol was not measured, so this says nothing about the hormone. The fatigue result was one secondary outcome among many measured, which makes a chance finding more likely. The trial was paid for by the extract's maker.Click to keep this openManage stress and anxiety
Sources5 behind this page

What we don't know

3 open questions