Ashwagandha (Withania somnifera) has gone from an Ayurvedic staple to one of the best-selling stress supplements in Australia and New Zealand. The marketing claims range from “reduces cortisol” to “clinical-grade anxiety relief.” Some of that is supported by evidence. Some of it isn’t. Here’s what the research actually shows.

What ashwagandha is supposed to do

Ashwagandha is classified as an adaptogen — a substance thought to help the body maintain balance under physical or psychological stress. The proposed mechanism involves modulating the hypothalamic-pituitary-adrenal (HPA) axis, which governs cortisol release. The active compounds are primarily withanolides, a class of steroidal lactones concentrated in the root.

The key question isn’t whether ashwagandha does something — several well-designed trials suggest it does. The question is how much it does, for whom, and under what conditions.

What the evidence shows

Cortisol reduction: Multiple randomised controlled trials (RCTs) have found statistically significant reductions in serum cortisol in adults with self-reported chronic stress. A frequently cited 2019 trial found participants taking 240mg of a standardised extract daily for 60 days had meaningfully lower morning cortisol compared to placebo. Effect sizes are real but modest — we’re not talking about pharmaceutical-level cortisol suppression.

Perceived stress and anxiety: Results here are more consistent. Several trials using validated tools (the Perceived Stress Scale, the Hamilton Anxiety Rating Scale) have found ashwagandha outperforms placebo on subjective stress measures. The effect tends to be clearest in people who were experiencing elevated stress at baseline — not in people who were already coping well.

Sleep: A secondary finding across several stress trials is improved sleep onset and sleep quality. This is plausible given cortisol’s role in the sleep-wake cycle, but dedicated sleep trials are limited.

Why the evidence is graded Moderate, not Strong

The trials that exist are generally well-designed, but there are real limitations worth understanding:

  • Sample sizes are small. Most trials run 40–80 participants. Larger independent replications are lacking.
  • Trial duration is short. Most run 8–12 weeks. Long-term effects — and long-term safety — are understudied.
  • Populations are narrow. Most trials recruit self-reported stressed adults, often from India. Generalisability to AU & NZ populations is reasonable but not confirmed.
  • Outcome measures vary. Some trials use serum cortisol, others use hair cortisol, others use only subjective questionnaires. This makes cross-trial comparison difficult.

The evidence is promising and consistent in direction. It doesn’t yet meet the bar for Strong because we’re missing large, independent, long-duration replications.

Extract type and dose matter more than most labels suggest

Not all ashwagandha products are equivalent. The research base is almost entirely built on standardised root extracts — KSM-66 and Sensoril (also called Shoden) are the two most studied proprietary extracts. Products using whole root powder, leaf extract, or unstandardised extracts have minimal clinical trial data.

Dosing ranges in trials: 240–600mg/day of standardised root extract, taken once daily or split into two doses. Most positive results fall in the 300–600mg range. Higher doses don’t appear to produce proportionally better outcomes and may increase the risk of gastrointestinal side effects.

Safety and contraindications

Ashwagandha has a reasonable short-term safety profile in healthy adults at studied doses. Points to be aware of:

  • Thyroid hormone interactions: Ashwagandha may increase thyroid hormone levels. People with thyroid conditions or taking thyroid medication should discuss this with their prescriber before use.
  • Pregnancy: Not recommended. Animal studies have raised safety concerns and human data is absent.
  • Autoimmune conditions: Theoretical concern that immune-stimulating properties could exacerbate autoimmune conditions. Evidence is limited but caution is warranted.
  • Liver: Rare case reports of hepatotoxicity have been published. Causality is not established, but people with liver conditions should be cautious.

Who is likely to benefit

The most consistent evidence supports use in adults experiencing genuine, elevated chronic stress — not as a daily supplement for people who are already well-regulated. If you’re sleeping well, managing stress effectively, and not experiencing HPA dysregulation, the expected benefit is small.

If you’re dealing with chronic work or lifestyle stress, disrupted sleep, and elevated baseline tension, the evidence is reasonable enough that a trial of 8–12 weeks with a standardised extract at 300–600mg/day is worth considering.

Bottom line

Ashwagandha is one of the better-evidenced adaptogens. The cortisol and stress findings are real, the effect sizes are modest, and the evidence quality is improving. It’s not a pharmaceutical intervention and it shouldn’t be marketed as one — but “stress miracle” undersells the nuance in both directions. For the right person, at the right dose, with the right extract, there’s something here.

Grade: Moderate — Consistent direction across multiple trials, but limited by small samples and short durations. Larger independent replications needed before upgrading to Strong.