Last reviewed September 2026
Most experts take: A few hundred mg in the afternoon or evening, for stress and sleep. Huberman uses it only for a few days at a time.
Best evidence: Stress, anxiety scores and cortisol, and sleep in people with insomnia, at 500-600 mg a day for at least 8 weeks.
Weakest evidence: Strength and muscle. Testosterone rises a little in men.
Skip it if: Pregnant or breastfeeding, or with thyroid, liver or autoimmune disease.
On this page: Which extract · What the experts take · Taken for vs shown to do · Who should skip it, and how much · How to choose
Which extract to buy
Most products use the root; some add the leaf, and the two have a different chemistry (NIH ODS). Trials have used several branded extracts at very different doses, so NIH says it is hard to name one best extract or amount. The practical rule: buy an extract that has its own trials, at the dose those trials used.
| Extract | Plant part | Trial dose | Note |
|---|---|---|---|
| KSM-66 – most used in trials | Root | 300 mg once or twice a day | Used in most of the sleep trials and several stress trials, including a 2012 trial of 64 stressed adults that lowered cortisol by 28% vs 8% on placebo. Standardised to 5% withanolides. |
| Shoden | Root and leaf | 120 mg a day | A 2020 trial of 150 adults with poor sleep found better sleep quality than placebo. The lowest dose of the four. |
| Sensoril | Root and leaf | 125-250 mg per capsule | Tested in stress trials (NIH). Labels state 10% withanolide glycosides. |
| NooGandha | Root and leaf | 225-400 mg a day | One 30-day US trial in 60 stressed adults (NIH). Used by Momentous. |
| Unbranded root extract | Root | Per label | No trials behind the product. The labels checked state 1.5-2.5% withanolides. |
What the experts take
Every linked row goes to the Fast Life Hacks article that documents it, with the podcast or video source.
| Expert | Dose | When | Brand |
|---|---|---|---|
| Andrew Huberman | 250-300 mg twice a day, for a few days to a week | Early afternoon and evening; not before training | Not stated |
| Peter Attia | 300 mg root extract | Before bed | Solgar |
| Bryan Johnson | 120 mg root and leaf, with 300 mg rhodiola | Morning | Blueprint (own brand) |
| Dale Bredesen | 500 mg twice a day (in his protocol) | With meals | Not stated |
| Kevin Rose | Not stated | Not stated | NOW |
| Andy Galpin | Not stated | Not stated | NSF-certified products for tested athletes |
Taken for vs shown to do
Almost all the trials are small, ran 6-12 weeks and were done in India. None tested using it for a few days at a time.
| Outcome | Who takes it for this | What the trials show |
|---|---|---|
| Stress and anxiety | Huberman, Galpin, Bredesen | ✅ Works, low certainty. A 2022 meta-analysis of 12 trials (1,002 people) found lower stress and anxiety scores, best at 300-600 mg a day, but rated the evidence low certainty. |
| Cortisol | Huberman, Attia, Galpin | ✅ Lowers it. A 2025 meta-analysis found lower cortisol, but in the same trials perceived stress did not differ from placebo. |
| Sleep | Attia, Galpin | ✅ Works, small. A 2021 meta-analysis of 5 trials found a small benefit, larger in people with insomnia, at 600 mg a day or more, and after 8 weeks or more. |
| Testosterone | Johnson (earlier stack), Galpin | ⚠️ Modest, in men. A 2026 meta-analysis of 23 trials found about 57 ng/dL higher testosterone in men and no change in women. |
| Strength with training | Nobody on this list | ⚠️ Weak. A 2026 meta-analysis found the strength gains depended on single trials and did not establish a meaningful effect. |
The main mismatch. Huberman stops after a week to avoid tolerance. No trial has tested tolerance, and the only report of trouble on stopping is a single case. He also avoids it before training, yet in a 2015 trial men taking 300 mg twice a day through 8 weeks of lifting gained more strength than placebo.
Who should skip it, and how much?
Ashwagandha is not a nutrient, so nobody is short of it. The trials enrolled stressed adults or people with insomnia, and that is where the benefit showed. The safety list matters more here than for most supplements:
- Pregnancy and breastfeeding. NCCIH says avoid.
- Thyroid disease or thyroid medication. It can raise thyroid hormones: a trial of 600 mg a day lowered TSH, and NIH lists three cases of thyrotoxicosis that resolved on stopping.
- Autoimmune disease, upcoming surgery, hormone-sensitive prostate cancer (NCCIH, NIH).
- Liver disease. Liver injury is rare but documented, usually jaundice and itching after 2-12 weeks that cleared after stopping (5 cases, 2020). In an Indian case series, three people with existing liver disease died.
Regulators. Denmark bans its sale as food after a risk assessment raised effects on sex hormones, reproduction and the thyroid (Danish Food Administration).
Dose figures from NIH ODS:
| Figure | Note | |
|---|---|---|
| Trial dose | 250-600 mg/day of root extract | Stress benefits looked bigger at 500-600 mg; Shoden trials used 120 mg. |
| Guideline | 300-600 mg/day (5% withanolides) | Provisional, for generalised anxiety disorder (WFSBP/CANMAT 2022). |
| Upper limit | None set | Not a nutrient, so no upper limit exists. |
| How long | Up to about 3 months | Well tolerated in trials that long; long-term safety is unknown. |
| When | No guidance | Most trials split it into two doses a day. |
Doses are what studies and experts used, not advice for you. See the medical disclaimer.
Medicines. NIH and NCCIH list possible interactions with thyroid hormone, diabetes and blood pressure medicines, immunosuppressants, sedatives and anti-seizure drugs. There is no spacing rule; inference: anyone on these should check with the prescriber first. Drowsiness and loose stools are the common side effects.
How to choose a product
Pick a single-ingredient product that names its extract, and take the dose that extract was tested at: 120 mg of Shoden and 600 mg of KSM-66 are not interchangeable. Ignore “highest withanolide %” claims: makers measure different compounds, so the percentages cannot be compared. Blends such as Johnson’s ashwagandha + rhodiola make it hard to tell what is working. Tested athletes need an NSF Certified for Sport product, as Galpin says.
Reputable brands of ashwagandha include:
| Product | Extract | Per capsule |
|---|---|---|
| Jarrow | KSM-66 | 300 mg |
| Natural Factors | KSM-66 | 600 mg |
| Life Extension | Sensoril | 125 mg |
| Momentous | NooGandha (NSF Certified) | 300 mg |
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Disclaimer: The above information is for research and educational purposes only and not a substitute for professional medical advice. See full medical disclaimer.
Note: We have no affiliation with the experts listed here - this page is based on publicly shared information.