Ashwagandha Benefits: The Cortisol Drops. Feeling Better Is a Separate Question.

Your cortisol will probably go down.

Whether you feel any better is a separate question, and the study that asked both got two different answers.

The finding that should frame everything else

In 2025 a systematic review did something unusually clean. It pooled two things from the same body of ashwagandha trials: cortisol — the stress hormone you can measure in blood — and Perceived Stress Scale scores, which is the questionnaire where people say how stressed they actually feel. [1]

Cortisol dropped, clearly and significantly. Perceived stress did not reach significance at all — p = 0.40, which means a result that far from the line is entirely compatible with nothing happening.

This is the oldest trap in health research and it has a name: a surrogate endpoint. Cortisol is a stand-in for stress. It is easy to measure, it moves, and it makes a great bullet point. The thing you actually care about — how you feel on a Tuesday afternoon — is harder to shift and harder to measure, and in this analysis it did not shift.

So does that settle it? No, and here is where it gets genuinely complicated rather than conveniently simple.

The number everyone quotes, and why it should worry you

The headline result for ashwagandha and anxiety comes from a 2022 meta-analysis of 12 trials in 1,002 people. It found a standardised mean difference of −1.55 for anxiety and −1.75 for stress. [2]

A standardised mean difference puts different studies on one scale: 0.2 is a small effect, 0.5 moderate, 0.8 large. So 1.55 is not just large. It is enormous — bigger than most prescription anxiety treatments report.

Which is exactly why you should look at the next number. The heterogeneity was 93.8%.

Heterogeneity is how much the individual trials disagree with each other. At 93.8% they disagree almost completely. An average computed across studies that found wildly different things is still an average, but it is not the reliable summary it looks like — it is a number sitting in the middle of a very wide argument.

The authors were straightforward about this. Their own assessment: “we identified that the certainty of the evidence was low for both outcomes,” and “further high-quality studies are needed to firmly establish the clinical efficacy of the plant.” [2]

That caveat is in the paper. It is almost never in the article quoting the paper.

Where the evidence is actually decent: sleep

This is the claim with the cleanest support, and it is not the one on the front of the bottle.

A 2021 meta-analysis of five randomised trials in 400 people found a significant effect on sleep — a standardised mean difference of −0.59, which is a moderate effect rather than a spectacular one. [3] It was larger in three specific circumstances: in people actually diagnosed with insomnia, at doses of 600 mg a day or more, and over treatment lasting at least eight weeks.

Ashwagandha also improved how alert people felt on waking. It did not significantly improve quality of life.

Worth knowing about that review, because it is unusually candid: it declares itself unfunded, it notes that all five trials were conducted in India, and it records that one of them was partly sponsored by the manufacturer. [3]

Ashwagandha for men and for women — the hormone numbers

A 2026 meta-analysis pooled 23 randomised trials covering 1,706 people and measured what actually happens to circulating hormones. [4] It is the most useful single answer to the men-versus-women question, because it reports both.

Cortisol fell, consistent with everything above (SMD −1.18). Serotonin rose. Testosterone in men rose by 57.43 ng/dL. In women it rose by 5.09 — effectively nothing, and the difference between the sexes was itself statistically significant. Estradiol did not move in either group.

What is 57 ng/dL? It is a real, measurable change, and it is not testosterone replacement therapy. We are deliberately not converting it into a percentage, because that needs a baseline the meta-analysis does not report, and a made-up denominator is exactly the trick this site exists to catch other people doing.

A broader 2021 review of 13 herbs across 32 studies puts it in context: ashwagandha and fenugreek were the two with positive testosterone findings in men, but across the whole field only 9 of 32 studies showed a statistically significant increase at all. [5]

The thyroid question, where two good studies disagree by population

This matters if you take thyroid medication, and the honest answer has two halves.

Pooled across those 23 trials in mostly healthy people, ashwagandha had no effect on TSH or T3, and raised T4 only modestly. [4]

But a 2018 trial ran specifically in 50 people with subclinical hypothyroidism — a mildly underactive thyroid without obvious symptoms — and found significant changes in all three: TSH, T3 and T4. [6] Its authors call it a pilot study.

Both can be true. In a healthy thyroid, not much happens. In one that is already borderline, the numbers move. If you are on levothyroxine or being monitored for thyroid function, that is a conversation with the person managing it — not because ashwagandha is dangerous to your thyroid, but because it is active on it, and your dose was calculated without it.

Side effects: the liver, reported properly

This is the part of the ashwagandha story that gets either ignored or turned into a scare. Neither is useful, so here is what is actually documented.

In 2020, a case series from Iceland and the US Drug-Induced Liver Injury Network described five people who developed liver injury after taking ashwagandha supplements. [7] All five became jaundiced. Onset came 2 to 12 weeks after starting. The injury was cholestatic — the bile-flow type — with prolonged itching and high bilirubin lasting 5 to 20 weeks. Nobody developed liver failure, and liver tests returned to normal within one to five months.

One detail in that paper closes off the usual escape hatch. Chemical analysis confirmed ashwagandha was in the supplements, and “no other toxic compounds were identified.” [7] This was not a contamination story. It was the herb.

Then a 2023 series from multiple centres in India reports the other end of the range. Among eight patients injured by single-ingredient ashwagandha, five had underlying chronic liver disease. Three of those arrived in acute-on-chronic liver failure. All three died. [8] In the patients without existing liver disease, the injury was prolonged but self-limiting — the same picture as Iceland.

So the risk is not one thing. It depends on the liver you already have.

Now the denominator, because scale matters

A 2026 scoping review searched the literature through December 2025 and found 13 publications describing 25 patients, worldwide, in total. [9]

Set that against how many people are taking these things. A 2024 analysis of national US survey data estimated that 15.6 million American adults had taken at least one of six liver-liable botanicals in the previous 30 days — a group that includes turmeric, green tea extract and ashwagandha. [10] The authors point out that this is comparable to the number of people prescribed simvastatin.

Twenty-five published cases against tens of millions of exposures means the individual risk is genuinely low. It does not mean zero, it does not mean the cases are not real, and it does not help you at all if you have cirrhosis.

What that comparison should actually make you notice is the asymmetry. The 15.6 million people on a botanical with liver liability have no prescriber, no baseline bloods, and no monitoring schedule. The 14 million on simvastatin have all three.

Dose, timing, and what the trials actually did

Dose. The stress trials used 300 mg twice daily [11] or 125–300 mg twice daily [12]. The sleep meta-analysis found effects were stronger at 600 mg a day or more. [3] So roughly 300–600 mg daily is the tested range.

Timing. The trials dosed twice a day, morning and evening. If your interest is sleep, the evening dose is the one doing the work in those protocols. None of these studies tested whether a particular hour matters, so anyone telling you there is a magic window is going beyond the evidence.

How long. Eight weeks or more, in the trials where the sleep effect was largest. [3] Nothing here is a same-week proposition.

One caveat that runs under all of it: the two most-cited stress trials both used the same branded extract, KSM-66, described as “provided by” and “manufactured and gifted by” its manufacturer. [11][12] The 2012 paper declares no funding and no conflict of interest, and that declaration deserves to be reported alongside the supply arrangement rather than instead of it. But it does mean the dose you buy may not be the material that was tested, and withanolide content — the active fraction — varies between products.

The verdict

Ashwagandha is not nothing, which makes it more interesting than most of what we check. It reliably lowers a stress hormone. It has a moderate, replicated effect on sleep. It nudges testosterone in men and not in women. It is measurably active on the endocrine system.

What it has not clearly done is make people report feeling less stressed — the one outcome the whole category is sold on. The analysis that measured cortisol and perceived stress side by side found the first and not the second. The analysis with the spectacular anxiety numbers carries 93.8% heterogeneity and a low-certainty rating from its own authors. And the evidence base is narrow: for sleep, five trials, all from one country, largely one supplier’s extract.

We have it at Preliminary. Something real is happening in the bloodwork. Whether it reaches the part of you that wanted the bottle is not yet established.

If you try it: the tested range is 300–600 mg a day for at least eight weeks, sleep is the claim with the best support, and you should talk to a doctor first if you have any liver condition, take thyroid medication, or are pregnant. If you develop jaundice, dark urine, or persistent itching, stop and get liver tests — that is the specific pattern in every one of those case reports, and it showed up between two and twelve weeks in.

What would move this to Supported: trials outside India, using extracts from more than one supplier, powered for perceived stress rather than cortisol, and reporting whether people felt better rather than whether their bloodwork did.

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