Ashwagandha: Benefits for Cortisol, Sleep, and Testosterone, Backed by Evidence

A look at what the research actually shows about this popular adaptogen, from stress hormones to sleep to strength.

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By the Ration Editorial Team · Reviewed against primary research · Updated July 13, 2026

Ashwagandha, or Withania somnifera, is a small shrub used in traditional Ayurvedic medicine for thousands of years.

Modern supplements use extracts of its root, sometimes combined with leaf material, standardized to contain compounds called withanolides.

It is classified as an adaptogen, a term for herbs believed to help the body resist physical and mental stress.

Most of the clinical research has focused on stress, cortisol, sleep, and, more recently, hormones and exercise performance.^[2]

Researchers think ashwagandha acts on the hypothalamic pituitary adrenal axis, the system that governs the body's release of cortisol in response to stress.^[8]

By modulating this axis, it may blunt the cortisol spike that comes with chronic stress, which is the mechanism most consistently supported by trial data.^[3]

Some proposed effects on GABA signaling in the brain may explain its reported influence on sleep onset and relaxation.^[11]

Its effects on testosterone and other hormones are less well mapped out, and the mechanism remains speculative.^[8]

Here is how our database grades the consistency and direction of ashwagandha's effects across available trials.

• ↓CortisolAHuman trials

  Research may lower Cortisol · strong agreement · 6 studies

  View 5 studies on PubMed

  • Effects of Ashwagandha (Withania Somnifera) on stress and anxiety: A systematic review and meta-analysis (2024)
  • Dual impact of Ashwagandha: Significant cortisol reduction but no effects on perceived stress - A systematic review and meta-analysis (2025)
  • An investigation into the stress-relieving and pharmacological actions of an ashwagandha (Withania somnifera) extract: A randomized, double-blind, placebo-controlled study (2019)
  • A standardized Ashwagandha root extract alleviates stress, anxiety, and improves quality of life in healthy adults by modulating stress hormones: Results from a randomized, double-blind, placebo-controlled study (2023)
  • 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 adults (2012)
• ↓Sleep Onset LatencyAHuman trials

  Research may lower Sleep Onset Latency · strong agreement · 6 studies

  View 5 studies on PubMed

  • Effect of Ashwagandha (Withania somnifera) extract on sleep: A systematic review and meta-analysis (2021)
  • The Impact of Ashwagandha on Stress, Sleep Quality, and Food Cravings in College Students: Quantitative Analysis of a Double-Blind Randomized Control Trial (2022)
  • Clinical evaluation of the pharmacological impact of ashwagandha root extract on sleep in healthy volunteers and insomnia patients: A double-blind, randomized, parallel-group, placebo-controlled study (2021)
  • The Perceived Impact of Ashwagandha on Stress, Sleep Quality, Energy, and Mental Clarity for College Students: Qualitative Analysis of a Double-Blind Randomized Control Trial (2022)
  • Withania somnifera (Ashwagandha) supplementation: a review of its mechanisms, health benefits, and role in sports performance (2025)
• ↑Total TestosteroneAHuman trials

  Research may raise Total Testosterone · strong agreement · 6 studies

  View 5 studies on PubMed

  • Do "testosterone boosters" really increase serum total testosterone? A systematic review (2024)
  • Examining the Effects of Herbs on Testosterone Concentrations in Men: A Systematic Review (2021)
  • An investigation into the stress-relieving and pharmacological actions of an ashwagandha (Withania somnifera) extract: A randomized, double-blind, placebo-controlled study (2019)
  • Examining the effect of Withania somnifera supplementation on muscle strength and recovery: a randomized controlled trial (2015)
  • Effect of an ashwagandha (Withania Somnifera) root extract on climacteric symptoms in women during perimenopause: A randomized, double-blind, placebo-controlled study (2021)
• ↑VO2maxDPreliminary

  Research may raise VO2max · strong agreement · 1 study

  View 1 study on PubMed

  • Efficacy and Safety of Low-Dose Ashwagandha Supplementation on Exercise Endurance: A Randomized, Placebo-Controlled, Double-Blind, Clinical Trial (2026)

Cortisol reduction has the strongest backing. A 2025 systematic review and meta-analysis found a significant, consistent lowering of cortisol across pooled trials, though it notably found no significant effect on perceived psychological stress scores, a split worth taking seriously.^[3]

A separate meta-analysis focused specifically on stress and anxiety outcomes did find improvements on validated anxiety and stress scales, so the picture across the literature is mixed depending on which outcome and which trials are pooled.^[5]

Individual randomized controlled trials have reported reduced self-rated stress and fatigue,^[6] improved quality of life via lower stress hormones,^[7] and better perceived sleep quality and food cravings in college students.^[9][10]

Sleep onset latency, meaning how long it takes to fall asleep, also has solid support. A placebo-controlled trial in both healthy volunteers and people with insomnia found ashwagandha root extract shortened time to sleep onset and improved subjective sleep quality.^[11]

Testosterone is where things get more nuanced. Ashwagandha is graded as increasing total testosterone with a strong evidence grade in our database, and a review of herbal supplements found it among the few herbs with reasonably consistent testosterone effects in men.^[12]

But a broader systematic review of commercial 'testosterone boosters' cautions that many products marketed this way show inconsistent or clinically small effects once you look across all available trials, so this is an area where enthusiasm should stay measured.^[4]

VO2max, a measure of aerobic exercise capacity, carries the weakest grade in our data, a D, based on just one trial.^[1] That 2026 randomized, placebo-controlled trial looked at low-dose ashwagandha and exercise endurance, but a single study is not enough to call this an established effect.^[1]

Clinical trials have used a range of standardized root extract doses, most commonly somewhere between 250 mg and 600 mg per day, taken once or split into two doses.^[6][7][11]

• Standardized root extract capsules, the most studied form
• Root extract combined with a small amount of leaf extract
• Powdered root, closer to traditional Ayurvedic preparation
• Gummies and drink powders, less studied but increasingly common

Trial durations have generally run from a few weeks up to about two months, so data on very long-term daily use is still limited.^[9][10]

• People experiencing high perceived stress or fatigue, where cortisol-lowering effects are best supported^[3][6]
• Those with mild difficulty falling asleep, given evidence for reduced sleep onset latency^[11]
• Men interested in testosterone support, with the caveat that broader reviews urge caution about overselling this effect^[4][12]
• Athletes curious about endurance gains, though this rests on a single small trial so far^[1]

Across the randomized trials reviewed, ashwagandha has generally been well tolerated at the doses studied, with mild gastrointestinal upset being the most commonly reported issue.^[2][6]

Because it may influence thyroid and reproductive hormones, people with existing thyroid conditions, those who are pregnant, or those on hormone-sensitive medications are often advised to be cautious, though dedicated long-term safety trials in these groups are limited.^[8]

As with most herbal supplements, product quality and withanolide content vary between brands, since supplements are not regulated as strictly as medications.

Ashwagandha has some of the more consistent supplement evidence out there for lowering cortisol and easing time to fall asleep.^[3][11]

Its effects on testosterone look promising in some analyses but are tempered by broader reviews questioning how meaningful 'testosterone booster' effects really are.^[4][12]

Claims about exercise performance, like VO2max, are still resting on very thin evidence and deserve a wait-and-see attitude.^[1]