Ashwagandha
Root extract (KSM-66 / Shoden)
Strong
Several good studies agree
Strong: a meta-analysis of 5 RCTs (n = 400) with consistent direction; objective actigraphy/PSG outcomes in 3 of them; replicated cortisol reductions across independent meta-analyses. Downgraded from 'definitive' because most trials are small and come from a handful of extract manufacturers.
In 5 studies, people slept noticeably better: they fell asleep faster, woke up less during the night and spent more of their time in bed actually asleep. Their stress hormone (cortisol) also dropped by about a quarter after two months at 600 mg.
Across five randomized trials, ashwagandha root extract improved objectively measured sleep — efficiency and time awake after sleep onset — and lowered serum cortisol by roughly a quarter at 600 mg per day. Effects need eight or more weeks and are largest in people who sleep poorly or feel stressed.
Withanolides appear to dampen the HPA stress axis (lower cortisol) and act on GABA-ergic signalling — calmer nights show up as fewer awakenings and higher overnight HRV.
Best in diagnosed insomnia and high perceived stress at ≥600 mg/day for ≥8 weeks. Little effect in already-good sleepers. Avoid with thyroid disease, pregnancy, autoimmune conditions.
What to buy
- ✓KSM-66 or Shoden branded root extract
- ✓600 mg/day dose (2 × 300 mg or 1 × 600 mg)
- ✓Third-party tested (USP, NSF, Informed Sport)
- ✕Leaf-based extracts or 'proprietary blends' without mg
- ✕Products bundled with melatonin if you want to isolate the effect
- · Rare liver-injury case reports (NIH LiverTox) — stop on dark urine/jaundice.
- · Raises thyroid hormones — avoid with hyperthyroidism or levothyroxine.
- · Avoid in pregnancy and autoimmune disease.
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Root-only extract standardized to 5% withanolides — the form used in the sleep and cortisol trials.
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Shoden is standardised to 35% withanolides, so 120–240 mg replaces 600 mg of KSM-66. Fewer capsules for the same withanolide load, and third-party tested.
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Raw root powder for smoothies — 3–6 g approximates 600 mg of extract. Seven thousand ratings, the best-reviewed powder here.
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See all on AmazonEvery result, next to the line that means no effect
Each diamond is a study's best estimate. The thin line shows how sure the study was: the shorter the line, the more certain the result.
- Sleep efficiency (SMD)SMD · Cheah 2021−0.68−1.06 … −0.30
- Sleep onset latency (SMD)SMD · Cheah 2021−0.53[not given]
- Wake after sleep onset (SMD)SMD · Cheah 2021−0.39[not given]
- Serum cortisol% · Chandrasekhar 2012−27.9%[not given]
Each unit gets its own scale, so numbers are never mixed on one line. When a study gave no range, we leave it blank instead of inventing one.
4 studies over 10 years
The studies
- 1.Effect of Ashwagandha (Withania somnifera) extract on sleep: A systematic review and meta-analysisPLOS ONE · 2021 · meta-analysis · 5 experiments · n = 400
Small-to-moderate overall sleep improvement (SMD −0.59); efficiency, latency, total sleep and WASO all improved; larger effects at ≥600 mg and ≥8 weeks.
- 2.A prospective, randomized double-blind, placebo-controlled study of safety and efficacy of a high-concentration full-spectrum extract of Ashwagandha root in reducing stress and anxiety in adultsIndian Journal of Psychological Medicine · 2012 · rct · n = 64
600 mg/day for 60 days reduced serum cortisol by 27.9% vs 7.9% with placebo.
- 3.Does Ashwagandha supplementation have a beneficial effect on the management of anxiety and stress? A systematic review and meta-analysis of randomized controlled trialsPhytotherapy Research · 2022 · meta-analysis · 12 experiments
Significant reductions in anxiety and stress scores versus placebo.
- 4.Ashwagandha — LiverTox: Clinical and Research Information on Drug-Induced Liver InjuryNIH / NCBI Bookshelf · 2019 · case reports
Rare cholestatic liver injury case reports; resolves on discontinuation.
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