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Strongest stress evidence

Ashwagandha

Withania somnifera

An adaptogen with the strongest meta-analysis evidence in the category for stress, anxiety, and cortisol modulation. KSM-66 and Sensoril are the two extracts with the most trial data.

Adaptogens Last verified 2026-05-06
stress and mood sleep

What it does

Ashwagandha (Withania somnifera) is the best-studied stress adaptogen. Multiple recent meta-analyses confirm reductions in perceived stress, Hamilton Anxiety scores, and serum cortisol. Sleep effects are smaller and emerge after 8+ weeks at 600 mg/day.

  • Stress and anxiety reduction Strong evidence

    2024 meta-analyses report reductions in Perceived Stress Scale (PSS -4.72) and Hamilton Anxiety scores (-2.19), plus lower serum cortisol vs placebo across multiple RCTs in stressed adults.

    Sources: PMID 39348746 · PMID 39083548

  • Sleep quality Moderate evidence

    Improvements in sleep onset latency, total sleep time, and sleep efficiency, strongest at 600 mg/day for 8+ weeks. Effect size larger in insomnia populations than in healthy sleepers.

    Sources: PMID 32818573 · PMID 34559859

  • Cortisol modulation Moderate evidence

    Lowered morning serum cortisol in chronically stressed adults; mechanism consistent with HPA-axis modulation underlying its adaptogen classification.

    Sources: PMID 34254920

Top picks

  1. 1

    Sports Research

    Ashwagandha 600 mg (KSM-66)

    KSM-66 600 mg matches the dose used in the Langade 2020 sleep trial.

    Check on Amazon
  2. 2

    Nature Made

    Ashwagandha 125 mg (Sensoril)

    Sensoril is root + leaf with higher withanolide concentration; lower per-cap dose.

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  3. 3

    NOW Foods

    Ashwagandha Extract 450 mg

    Generic extract; verify withanolide standardization on the COA.

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How to use it

Dosage
300 to 600 mg/day root extract standardized to at least 5% withanolides. 300 mg twice daily is the most-replicated split.
Timing
Once or twice daily. Evening dose helpful if sleep is the target.
With food
Yes
Onset
6 to 8 weeks for stress and anxiety; 8+ weeks for sleep.

What to look for

  • Extract identity disclosed: KSM-66 (root-only, ~5% withanolides) or Sensoril (root + leaf, >=10% withanolides).
  • Withanolide standardization disclosed numerically, not 'high potency'.
  • Root-only vs root-and-leaf disclosed; root-only (KSM-66) is the form used in most cortisol trials.
  • Third-party testing for identity, heavy metals, pesticides (USP, NSF, Informed Choice).
  • Dose-per-serving matches trial doses (300 to 600 mg/day) without proprietary blends.

Formats: capsules, powder, gummies.

Skip if:
  • Pregnancy or breastfeeding (potential abortifacient activity per NIH ODS).
  • Thyroid disorders or concurrent thyroid medication (raises T3/T4, lowers TSH).
  • Pre-existing liver disease (case reports of liver injury 2 to 12 weeks after start; LiverTox NBK548536).
  • Concurrent sedatives, immunosuppressants, antihypertensives, or antidiabetic drugs.

FAQ

KSM-66 vs Sensoril, which is better?
KSM-66 is full-spectrum root-only and tracks closer to the trials cited above; Sensoril is concentrated on a fraction with stronger cortisol effects but a more sedating profile. Pick KSM-66 for daytime, Sensoril for evening or sleep.
Can I take it long-term?
Trials up to 12 months show no major safety concerns in healthy adults. Liver-injury case reports exist but are rare; stop and consult a clinician if you develop unexplained fatigue or RUQ pain.

Related comparisons

Additional references