What is Ashwagandha?

What is Ashwagandha?

Ashwagandha is the root of Withania somnifera, a small shrub used in Ayurvedic medicine for more than 3,000 years and classified today as an adaptogen — a substance said to help the body handle physical and psychological stress without over-stimulating or sedating it. The name comes from Sanskrit: ashva means horse and gandha means smell, a reference both to the root's strong odor and to the traditional claim that it confers a horse's strength and vitality.

Modern extracts concentrate the root's withanolides, a family of steroidal lactones (withaferin A and withanolide A are the best studied), and standardize the finished powder to a stated withanolide percentage so a capsule delivers a consistent dose instead of the variable potency of raw plant material. You will see it marketed as a stress and cortisol supplement, a sleep aid, and, more recently, a strength and recovery aid for lifters, on the strength of trials showing gains in bench-press strength and testosterone alongside resistance training. It is sold as capsules, standardized extract powders (KSM-66, Sensoril, Shoden), and traditional churna powder, with the extract forms carrying almost all of the clinical evidence behind the dosing guidance below.

How it works

Ashwagandha's best-documented mechanism runs through the hypothalamic-pituitary-adrenal (HPA) axis, the hormonal chain that releases cortisol when your brain perceives a threat. In randomized trials, 250–600 mg of standardized root extract taken daily for 4–12 weeks lowers morning serum or salivary cortisol compared with placebo, and blunting that curve is the leading explanation for the supplement's effects on perceived-stress and anxiety scores.

A second, separate pathway involves gamma-aminobutyric acid (GABA), the brain's main inhibitory neurotransmitter: withanolides appear to bind GABA-A receptors and increase GABAergic signaling, the proposed reason ashwagandha shortens the time it takes to fall asleep and increases total sleep time in trials using 600 mg/day for 6–8 weeks. A third mechanism, relevant to lifters, is antioxidant and anti-inflammatory activity — withanolides scavenge reactive oxygen species and blunt exercise-induced oxidative stress, one proposed reason a resistance-training trial found a smaller rise in creatine kinase (a muscle-damage marker) in the ashwagandha group after training. None of these three mechanisms fully explains the modest testosterone increase (roughly 15–17%) seen in some resistance-training trials; the leading hypothesis is that lower cortisol frees up more of the shared cholesterol-derived steroid precursor pool for testosterone synthesis, since cortisol and testosterone compete for it, but this pathway is inferred from hormone panels rather than measured directly.

The scale

There is no single equation, but clinical dosing clusters around a consistent pattern: match the dose and duration to the goal, and give it weeks, not days, to work.

How to apply it

• Match the dose to the goal: 300 mg twice daily (600 mg total) is the dose behind the strength and testosterone data; 250–500 mg once daily is what most stress and anxiety trials used. Buying a product without checking which dose your goal actually needs is the most common mistake.
• Take it daily, not as-needed: Effects build through the HPA axis over weeks. A single dose before a stressful meeting or a big lift will not reproduce the trial results, which all involved consistent daily dosing over 6–12 weeks.
• Give it 6 to 8 weeks before judging: Most positive stress trials ran 8–12 weeks and most sleep trials ran 6–8 weeks. Stopping after two weeks because you "don't feel anything" quits before the window most benefit showed up.
• Buy a standardized extract with third-party testing: Look for a stated withanolide percentage (for example, "5% withanolides") and a certificate of analysis. Unstandardized raw powders vary batch to batch in potency and can carry higher heavy-metal loads.
• Split higher doses across the day: 600 mg is usually taken as two 300 mg doses, morning and evening, which is how the strength trial dosed it and how most users tolerate it best, rather than as one large dose that can upset the stomach.
• Recheck bloodwork on long-term or high-dose use: Liver-injury case reports cluster at doses above 600 mg/day or courses longer than 8–12 weeks. A baseline ALT/AST/bilirubin panel and a follow-up at 8–12 weeks is a reasonable precaution, not paranoia.

Types

Worked example

The most-cited resistance-training trial (Wankhede et al., 2015) put 57 untrained young men through 8 weeks of structured strength training, half taking 300 mg of ashwagandha root extract twice daily (600 mg total) and half taking a matched placebo. Here is what changed in each group.

Both groups followed the identical training program, so the gap between them is the variable of interest — but the trial cannot separate a direct hormonal effect from lifters simply recovering better and training harder because they felt less beat up. Treat this as the single largest effect size in the ashwagandha strength literature, not a guaranteed outcome; it has not been reproduced at this magnitude in every follow-up trial.

Ashwagandha vs rhodiola rosea

Some lifters stack a morning dose of rhodiola for training focus with an evening dose of ashwagandha for cortisol and sleep. The two don't compete for the same receptor pathway, so there's no established interaction risk, but you're still combining two herbs that individually lack large, long-term safety trials.

By goal

• General stress and everyday recovery: Take 300–600 mg/day of a standardized extract consistently for at least 8 weeks before judging whether it's working. Track a simple weekly stress rating rather than guessing, since the effect builds gradually rather than announcing itself.
• Strength and hypertrophy training: 600 mg/day (300 mg twice daily) alongside a structured resistance program is the dose behind the largest strength and testosterone signal in the literature. Treat it as a recovery aid that may let you handle more training volume, not a replacement for progressive overload or adequate protein.
• Sleep-focused use: A higher-withanolide extract (Sensoril-style, 8–10%) at 600 mg taken in the evening has the best sleep-specific trial data. Give it 6–8 weeks and pair it with consistent sleep and wake times, since the sleep effect size is smaller than the stress effect.

Common misconceptions

• "Ashwagandha spikes testosterone into steroid-like territory." The largest reported increase in a resistance-training trial was about 96 ng/dL, roughly 15–17% above baseline — a modest hormonal shift, not remotely comparable to anabolic steroid use. The strength gains in that trial are better explained by lower cortisol and improved recovery than by a direct testosterone surge.
• "A higher withanolide percentage always means a stronger or safer extract." Bioavailability depends on the specific withanolide glycosides present, not just the total percentage; a crossover study found a 40%-withanolide extract produced dozens of times more absorption per milligram than a 2.5% extract. Higher-dose products have also produced more of the liver-injury case reports, so more is not automatically better or safer.
• "It works the same day, like a sedative or an anti-anxiety pill." Ashwagandha modulates the HPA axis over time; clinical trials measuring stress and anxiety ran 8–12 weeks and sleep trials ran 6–8 weeks before showing their effects. Taking one dose before a stressful event does not reproduce those results.
• "It's an herb, so it's automatically safe to take indefinitely." A 2020 case series documented five people who developed jaundice and liver injury after taking ashwagandha, and it is a firm contraindication in pregnancy and in hyperthyroidism or Graves' disease. Anyone with liver disease, thyroid disease, an autoimmune condition, or who is pregnant or breastfeeding should talk to a clinician first.

Related terms

Ashwagandha FAQ

What is ashwagandha used for?

Ashwagandha is used mainly for stress and anxiety, where a standardized root extract at 250–600 mg/day for 8–12 weeks lowers cortisol and perceived stress in trials. It's also used for sleep quality and, among lifters, as a recovery aid alongside resistance training, where it's linked to modest strength and testosterone gains.

Does ashwagandha actually lower cortisol?

Yes, in most randomized trials. A 2023 trial found morning cortisol fell in 64% of people taking 500 mg of standardized root extract for 60 days, versus 24% on placebo. Results vary by study and extract, but cortisol reduction is ashwagandha's most consistently replicated finding.

How long does ashwagandha take to work?

Expect 2–4 weeks before noticing a change in stress or anxiety, and 6–8 weeks for sleep quality to improve, based on trial timelines. It's not a fast-acting sedative — a single dose before a stressful event won't reproduce the clinical results, which all involve daily dosing over weeks.

What is the best dose of ashwagandha to take?

Most clinical benefit comes from 300–600 mg/day of root extract standardized to 5% withanolides, split into one or two doses. Stress and anxiety trials commonly used 250–500 mg/day; the strength and testosterone trial used 600 mg/day (300 mg twice daily) for 8 weeks.

Does ashwagandha increase testosterone?

In one 8-week resistance-training trial, men taking 600 mg/day saw serum testosterone rise about 96 ng/dL (roughly 15–17%) versus a much smaller placebo change. The increase is modest, not steroid-like, and is better explained as a side effect of lower cortisol and improved recovery than a direct hormonal driver.

Can ashwagandha help you sleep?

It can, modestly. Trials using 600 mg/day of a higher-withanolide extract for 6–8 weeks report better sleep quality, faster time to fall asleep, and fewer night wakings versus placebo. The effect is smaller than for stress and anxiety, and works best alongside consistent sleep timing rather than as a stand-alone fix.

What is the difference between KSM-66 and Sensoril ashwagandha?

KSM-66 is a root-only extract standardized to about 5% withanolides using a water-and-milk process, and has the deepest evidence base for stress, strength, and testosterone. Sensoril is a root-and-leaf extract standardized to 8–10% withanolides, water-extracted, and is best studied for sleep quality.

Is it safe to take ashwagandha every day?

For most healthy adults, 300–600 mg/day for up to 8–12 weeks appears well tolerated in trials, with mild stomach upset or drowsiness as the main complaints. Doses above 600 mg/day or courses longer than a few months carry more of the rare liver-injury case reports, so periodic bloodwork is a reasonable precaution.

Who should not take ashwagandha?

Avoid it during pregnancy and while breastfeeding, and if you have hyperthyroidism or Graves' disease, since it can raise thyroid hormone levels. Use caution with autoimmune conditions, liver disease, or if you take thyroid, blood sugar, sedative, or blood pressure medication, and check with a clinician before combining them.

Can ashwagandha damage your liver?

Rarely. A 2020 case series documented five people who developed jaundice and cholestatic or mixed liver injury 2–12 weeks after starting ashwagandha, with recovery in one to five months and no liver failure. It's uncommon, but it's why high doses and long courses warrant a baseline and follow-up liver panel.

References

1. Majeed M, et al. 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. Medicine (Baltimore), 2023. PubMed 37832082
2. Sprengel M, et al. Withania somnifera (Ashwagandha) supplementation: a review of its mechanisms, health benefits, and role in sports performance. Nutrition & Metabolism (London), 2025. PubMed 39910586
3. Wankhede S, et al. Examining the effect of Withania somnifera supplementation on muscle strength and recovery: a randomized controlled trial. J Int Soc Sports Nutr, 2015;12:43. PubMed 26609282
4. Kim SK, et al. Pharmacokinetics and bioequivalence of Withania somnifera (Ashwagandha) extracts — A double blind, crossover study in healthy adults. Heliyon, 2023. PubMed 38144272
5. Björnsson HK, et al. Liver Injury due to Ashwagandha: A Case Series from Iceland and the U.S. Drug-Induced Liver Injury Network. Liver International, 2020. PubMed 31991029
6. Ashwagandha: Usefulness and Safety. National Center for Complementary and Integrative Health (NCCIH)
7. Ashwagandha: Uses and Side Effects. Cleveland Clinic