Ashwagandha: effects, side effects and risks, and how to test it on yourself

Updated: 2026-09-25

Ashwagandha has real meta-analytic support for reducing perceived stress and anxiety — the effect sizes are moderate to large across several independent reviews. It also has a real, documented downside: multiple published case reports of liver injury and at least two of thyrotoxicosis. Separately, Denmark now bans it as a food supplement. Below: the actual numbers from both sides, and a Health OS protocol to test the stress effect on yourself.

What the meta-analyses on stress and anxiety show

A 2022 meta-analysis of 12 RCTs (1,002 participants, ages 25-48) found ashwagandha significantly reduced both anxiety (SMD -1.55, 95% CI -2.37 to -0.74) and perceived stress (SMD -1.75, 95% CI -2.29 to -1.22) versus placebo. A separate 2024 meta-analysis of 9 RCTs (558 patients) found a similar direction: Perceived Stress Scale down by 4.72 points, Hamilton Anxiety Scale down by 2.19 points, and serum cortisol down by 2.58 vs. placebo.

Both reviews rated the certainty of evidence as low, and heterogeneity between trials was high (I² in the 83-94% range) — the studies used different extracts, doses and populations. The 2022 meta-analysis found the stress benefit was strongest at 300-600 mg/day; anxiety benefit was reported across doses up to 12,000 mg/day, well above the 600 mg/day the Health OS protocol uses.

What about sleep specifically

A dedicated 2021 meta-analysis of 5 RCTs (400 participants) found ashwagandha had a small-to-moderate effect on overall sleep (SMD -0.59, 95% CI -0.75 to -0.42). The effect was more pronounced in people already diagnosed with insomnia, at doses ≥600 mg/day, taken for ≥8 weeks. It also improved morning alertness, but not quality-of-life scores.

That duration threshold matters: the Health OS "Ashwagandha KSM-66" protocol runs a 21-day intervention phase at 600 mg/day — the right dose, but well under the 8 weeks the sleep meta-analysis flags as where the effect is "more pronounced." Don't be surprised if 3 weeks understates the real effect; the protocol's own interpretation notes say the effect is cumulative and to weight the later days of the intervention phase more.

Documented side effects

Ashwagandha has multiple published case reports of drug-induced liver injury. A 2023 review applying the updated RUCAM causality tool pooled the previously reported cases and added two new ones: a 36-year-old man took 450 mg of ashwagandha three times a day for 6 months and then developed nausea, itching and dark-colored urine; a 30-year-old woman developed itching after 45 days on 450 mg. Both cases showed elevated bilirubin and liver enzymes (AST, ALT, ALP); the RUCAM score (7 in both) indicated a "probable" link to ashwagandha, and both improved after stopping the supplement.

A separate 2023 case report specifically warns that ashwagandha can trigger life-threatening acute-on-chronic liver failure in people who already have liver disease. None of this means liver injury is common — these are case reports, not incidence data — but it is a documented, real risk, not a hypothetical one.

Thyroid: a mechanism worth knowing about

A 2005 case report documented a healthy 32-year-old woman who developed lab-confirmed thyrotoxicosis while taking ashwagandha for fatigue; her symptoms resolved after she stopped. A small safety substudy inside an unrelated 2014 bipolar-disorder trial found a similar signal: all 3 ashwagandha-treated patients had their T4 levels rise from baseline (+7%, +12%, +24%), while 6 of 7 placebo patients' T4 fell — the authors called it a reason for "vigilance regarding hyperthyroidism."

Separate from these case reports, a regulator has independently pointed the same way: Denmark's food safety authority (Fødevarestyrelsen) now classifies ashwagandha as illegal to sell as a food or supplement there — its official reasoning cites effects on sex hormones and reproduction, plus effects on metabolism, the immune system and the central nervous system, based on a separate risk assessment from the Danish Technical University. It's a single-country regulatory call, not a global consensus, and it isn't clear whether it draws on the same cases described above.

Who should be careful — or skip it

Combining the sourced risks above with the Health OS protocol's own safety rules: avoid ashwagandha if you have hyperthyroidism (it may push thyroid hormone higher), if you're pregnant, or if you're on immunosuppressants or sedative medication without medical guidance. Given the liver case reports, anyone with pre-existing liver disease should be especially cautious and talk to a doctor first.

Stop and see a doctor if you notice: nausea, itching or unusually dark urine (the symptoms from the case reports above), GI upset lasting more than 3 days, drowsiness that interferes with work, an allergic reaction, or thyrotoxicosis symptoms — tremor, a rapid heartbeat, weight loss (these last four are the Health OS protocol's own stop conditions).

How to test it on yourself with Health OS

The "Ashwagandha KSM-66" protocol runs 7 days of baseline, then 21 days of 300 mg KSM-66 in the morning plus 300 mg in the evening (600 mg/day total, with food) — the dose the sleep and stress meta-analyses above associate with the clearest effects. Primary outcomes are self-rated evening stress and Oura HRV; secondary checks are sleep score and resting heart rate.

Success in the protocol is defined as stress dropping by at least 1.5 points, or HRV rising at least 8% relative to baseline, with a minimum of 14 nights of data. Given the meta-analysis finding that longer use shows a stronger effect, weight the last week of the intervention phase more heavily than the first — and if you have any thyroid history, track temperature deviation and resting heart rate as an extra safety check, per the protocol's own interpretation notes.

FAQ

What are the actual benefits of ashwagandha?

The best-supported effects, across several independent meta-analyses, are reduced perceived stress and anxiety (moderate-to-large effect sizes vs. placebo) and modestly better sleep, especially at ≥600 mg/day for 8+ weeks. All reviews rate the certainty of this evidence as low, due to high heterogeneity between trials.

What are ashwagandha's side effects?

In the RCTs reviewed in the meta-analyses above, reported adverse events were mostly mild-to-moderate and safety/tolerability didn't differ significantly from placebo. Separately, outside those RCTs, multiple published case reports describe serious liver injury and at least two describe thyrotoxicosis — rare compared to trial-reported side effects, but real and documented.

Is ashwagandha dangerous?

A 2025 meta-analysis of 14 RCTs in people with mental disorders (mostly anxiety; median dose 600 mg/day, median follow-up 8 weeks) found no significant difference in safety and tolerability compared to the comparators used — but that's data from that specific population, not healthy people in general. It isn't risk-free: published case reports link it to liver injury (including one case of life-threatening acute-on-chronic liver failure in someone with pre-existing liver disease) and to thyrotoxicosis.

How does ashwagandha actually work / what is it used for?

It's most studied as an "adaptogen" for stress and anxiety, with the meta-analyses above showing reduced Perceived Stress Scale and Hamilton Anxiety Scale scores, plus a modest drop in serum cortisol, versus placebo. It's also studied for sleep quality at the same dose range. This guide sticks to what the human trials measured, not proposed mechanisms.

Can I take ashwagandha if I have thyroid problems?

Be cautious. Case reports and a small safety substudy both found signals of ashwagandha raising thyroid hormone levels, and the Health OS protocol itself lists hyperthyroidism as a contraindication. If you have any thyroid condition, talk to your doctor before starting, and stop immediately if you notice tremor, a racing heartbeat, or unexplained weight loss.

Is ashwagandha legal everywhere?

No. Denmark's Fødevarestyrelsen classifies it as illegal to sell as a food or food supplement there, citing effects on sex hormones and reproduction, metabolism, the immune system and the central nervous system, based on a Danish Technical University risk assessment. Regulations vary by country — check local rules before ordering.