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Ashwagandha

Withania somnifera · Brain

ModerateSeveral human trials, smaller or less consistent.

Adaptogenic herb studied for perceived stress and cortisol.

~5% withanolides
The KSM-66 standardization behind most positive trials, unstandardized powders can be anything

What it is

A root used in Ayurvedic medicine, now one of the most-sold "adaptogens" in the West, taken mostly for stress and sleep. It has better human trial support than most herbals, and a real safety signal that most product pages leave out.

How it works

The active compounds (withanolides) appear to dampen the HPA axis, the stress circuit that ends in cortisol release. Lower the cortisol response and the downstream feelings of stress, and sleep onset, tend to follow. That is the plausible story; the trials are small enough that "appear to" is doing real work in that sentence.

Which form to buy

KSM-66The most-studied extract

Root-only, standardized to ~5% withanolides; the branded ingredient in a large share of the stress trials.

The option with the most trial data behind it.

SensorilA different standardization

Root-and-leaf extract with higher withanolide content. The daytime-vs-evening split between the two brands is positioning, no comparative trial establishes it.

Also standardized; less trial data than KSM-66.

Generic "ashwagandha root powder"Budget

Unstandardized: withanolide content varies enormously between products, so trial doses do not transfer. NIH notes this heterogeneity is exactly why confident product or dose guidance is not possible.

What is actually in it is unknown.

GummiesConvenience

Check the extract and amount against what trials used, and the sugar.

Varies enormously by product.

What it actually does, graded

Reduces perceived stress and anxietyModerate

The most replicated finding, consistent improvements on stress scales across several small RCTs, usually 8 weeks.

Lowers cortisolModerate

Reductions shown in multiple trials, though cortisol is a noisy marker and the studies are small.

Improves sleepModerate

Meta-analysed benefit on sleep quality, strongest in people who started with insomnia.

Raises testosteroneLimited

Some small trials in stressed or infertile men show increases; not established in healthy men with normal levels.

Strength and muscle gainLimited

A handful of small resistance-training studies with modest effects; nowhere near creatine's evidence base.

Pros and cons

Pros
  • Among the better-evidenced herbals for stress, which is a low bar it genuinely clears
  • The standardized extracts let you match what trials actually used
  • Effects, where they occur, show up within weeks rather than months
Cons
  • Liver injury reports are real and documented, rare, but this is not an inert herb
  • It can push thyroid hormone levels up, which matters if yours are already managed
  • Trials are small, short, and often industry-funded
  • Sedation is common enough that daytime dosing does not suit everyone

What to expect

  • Sleep effects are reported by some people early on, though trials did not measure time-to-onset.
  • Stress-scale improvements were measured at the 8-week mark in most trials, a slow-building effect rather than a dose-and-feel-it one.
  • Any time: dark urine, yellowing skin or eyes, or unusual fatigue means stop and get liver enzymes checked.

Interactions

CautionThyroid medicationAshwagandha can raise thyroid hormone levels; on levothyroxine that can tip toward overtreatment. Prescriber should know.
CautionSedatives, sleep drugs, alcoholAdditive sedation, a stronger effect than people expect.
AvoidImmunosuppressantsIt may stimulate immune activity against the drug's purpose, a transplant-rejection case has been reported.
CautionDiabetes, blood pressure and anticonvulsant medicationNCCIH lists possible interactions with all three. These are potential rather than well-quantified, raise them with your prescriber.
AvoidExisting liver diseaseGiven documented liver-injury case reports, this is not the herb to experiment with on a compromised liver.
AvoidPregnancyTraditionally contraindicated and not established as safe.

Is it for you?

Probably worth it if
  • Chronic stress or a racing mind at bedtime
  • You want something with actual trial data rather than vibes
  • You are prepared to give it the ~8 weeks the trials ran, rather than judging it in days
Probably skip it if
  • You are chasing a testosterone boost with normal levels, that is not what the data shows
  • You already take a sedating medication

Who should avoid it

  • Anyone with liver disease or a history of drug-induced liver injury
  • People pregnant or breastfeeding
  • Anyone on thyroid medication, without their prescriber involved

Research on this supplement

Papers about this supplement, not proof of the claims above. A title says what was studied, which is sometimes a negative result or a different question entirely.

  • Effects of Ashwagandha (Withania Somnifera) on stress and anxiety: A systematic review and meta-analysis
    Explore (NY), 2024
  • Does Ashwagandha supplementation have a beneficial effect on the management of anxiety and stress? A systematic review and meta-analysis of randomized controlled trials
    Phytother Res, 2022
  • Effect of Ashwagandha (Withania somnifera) extract on sleep: A systematic review and meta-analysis
    PLoS One, 2021

What the evidence says

Multiple human RCTs show reduced perceived-stress scores. Trials are mostly small, short, and often manufacturer-funded.

What studies used

300-600 mg of a standardised extract daily. Daily, often evening.

Reported from published studies and product labelling — a record of what was used in research, not a recommendation. What is right for you is a conversation with a clinician.

Watch out for

  • Rare but real reports of liver injury
  • Can blunt emotional range at higher doses
  • Not for thyroid conditions without medical input

Evidence base

A893 research papers
established literature

Strong human evidence: either a phase 3 or 4 trial report alongside review-level evidence, or ten or more randomised controlled trial reports.

This letter measures how much human research exists, not whether it works for you — the tier above (Moderate) is the read on quality.

Research (12)

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Where next

Every supplement in the catalogThe full shelf, grouped and evidence-tiered.→The compound indexSteroids, nootropics and research chemicals.→The peptide indexInjectable peptides and what trials used.→