Ashwagandha

What is ashwagandha?

Ashwagandha (Withania somnifera) is a shrub whose root has been used in Ayurvedic medicine for about 3,000 years. It is called an adaptogen, a term for herbs proposed to help the body respond to stress. Unlike many herbs in that group, standardized ashwagandha extracts have randomized human trials.

Its marker compounds are withanolides, steroid-like lactones concentrated in the root, and nearly everything that matters about an ashwagandha product reduces to two questions: how many milligrams, and at what withanolide standardization.

The forms that matter

The standardization percentage is the single most important line on the label: 250 mg at 1.5% withanolides delivers ~3.75 mg of active ingredients where the trial benchmark (KSM-66 at 5%, 300–600 mg) delivers ~15–30 mg.

Where does it come from?

India, the Middle East, and North Africa; the root is the medicinal part. Ayurvedic texts prescribed it for exhaustion, insomnia, and male vigor, strikingly close to its modern positioning.

How does ashwagandha work in the body?

The best-supported mechanism is HPA-axis modulation: it blunts the brain-adrenal cascade that releases cortisol under stress, and cortisol reduction is the finding that repeats most consistently across trials. Because cortisol suppresses testosterone and disrupts sleep, a cortisol effect plausibly cascades into the hormone and sleep findings, which is why researchers describe the testosterone data as secondary, not direct.

Withanolides also show GABA-mimicking activity (a sedative-adjacent pathway, explaining sleep effects), anti-inflammatory effects in lab work, and mild thyroid-stimulating activity, that last one being a documented interaction, not just a benefit claim.

What is ashwagandha claimed to do?

The full marketing stack: stress and anxiety relief, better sleep, higher testosterone, muscle growth and recovery, male fertility, thyroid support, cognitive enhancement, and general “adaptogenic” resilience. Several of these have human trial support; a few are extrapolation.

What does the research show?

Stress and cortisol — the main ingredient finding

Small trials found reduced perceived stress and cortisol with standardized ashwagandha extracts. Their short duration and manufacturer links limit how broadly the results apply.

Chandrasekhar et al. (2012, Indian J Psychol Med): 64 adults with chronic stress, randomized to 300 mg KSM-66 twice daily or placebo for 60 days. Serum cortisol fell 27.9% in the ashwagandha group vs 7.9% on placebo; perceived-stress scores dropped 44%; anxiety subscales improved comparably. Limitations: manufacturer-linked research, 8-week duration, and stress was self-reported, though cortisol is an objective marker.

Lopresti et al. (2019, Medicine): 60 adults, 250 mg or 600 mg/day standardized extract for 8 weeks. Both doses beat placebo on stress measures; cortisol decreased, and in men, testosterone and DHEA-S rose. Notable for showing a dose-response signal and a male-hormone effect in the same trial.

Sleep

Small trials found improved sleep measures with standardized ashwagandha extracts. The reported effect was modest and does not establish long-term benefit.

Langade et al. (2019, Cureus): 60 insomnia patients, 300 mg KSM-66 twice daily for 10 weeks, improved sleep quality, time-to-sleep, and sleep efficiency versus placebo, with larger effects in insomnia patients than healthy sleepers. A later meta-analysis of the sleep trials graded the effect significant but modest: it helps you sleep; it isn’t a sedative.

Strength, muscle, and testosterone

Small trials found strength and hormone changes with specific extracts in particular groups of men. They do not establish the same benefit for every ashwagandha preparation.

Wankhede et al. (2015, JISSN): 57 young men in an 8-week resistance-training program, 300 mg KSM-66 twice daily. Versus placebo: significantly greater gains in bench-press and leg-extension strength, larger muscle-size increases, better recovery markers, and testosterone rising roughly 5× the placebo increase. The strength effect in already-training men is the standout, though it’s one trial.

Lopresti et al. (2019, Am J Men’s Health) in aging males: 300 mg twice daily for ~16 weeks raised DHEA-S ~18% and testosterone ~11–18% versus placebo, a modest endocrine nudge consistent with the cortisol-mediated mechanism, not hormone therapy.

Male fertility

One small pilot found improved sperm measures in men with low sperm counts. Independent replication is needed; the result does not establish improved fertility in the general population.

Ambiye et al. (2013): 46 low-sperm-count men, 675 mg/day for 90 days: sperm concentration +167%, semen volume +59%, motility +57%, serum testosterone +17% versus placebo. Striking numbers, but a small pilot in infertile men, the population most likely to show large gains, and it awaits independent replication.

Thyroid — benefit and interaction in one finding

One trial found changes in thyroid hormones in adults with subclinical hypothyroidism. That also makes thyroid conditions and thyroid medicines important safety considerations.

Sharma et al. (2018, J Altern Complement Med): 50 subclinical-hypothyroid patients, 600 mg/day for 8 weeks: T3 and T4 rose significantly and TSH normalized in a subset versus placebo. For mild hypothyroidism that’s a benefit; for hyperthyroid patients or anyone on levothyroxine it’s a documented reason to be careful.

What doesn’t ashwagandha do?

It doesn’t treat anxiety disorders; it lowers perceived stress, which is a different claim. Cognition claims (memory, focus) rest on thin, inconsistent trials. And it doesn’t raise testosterone like a hormone therapy does: the endocrine effects are real but modest, and plausibly disappear if your cortisol wasn’t elevated to begin with.

Research gaps: no trials past ~16 weeks; nearly all positive trials are manufacturer-linked or Indian single-site studies; and the effect in healthy, non-stressed, well-rested adults is essentially uncharacterized.

What dose was studied?

The pattern is unmistakable: 600 mg/day of a ~5%-withanolide extract is where the literature lives. Below ~240 mg/day there is weak trial support, and at low standardization the active load falls further.

Which form is best?

KSM-66 for stress/strength data, Sensoril for higher withanolides (sleep-leaning, more sedating profile). Generic extracts with a stated withanolide percentage are second-best; unstandardized root powder is a different product at a fraction of the active load.

How and when to take it

Trials split 300 mg morning and evening; sleep-focused use favors evening dosing. With food if it upsets your stomach. Given the unknown long-term data and rare liver-injury reports, many clinicians suggest cycling (e.g., 8–12 weeks on, 2–4 off); that’s practice convention, not trial-tested guidance.

Side effects

Common: mild digestive upset, drowsiness (a feature if you wanted sleep). Rare but real: liver-injury case reports collected in LiverTox, mostly cholestatic patterns after weeks-to-months of use, reversible on stopping. Also reported: over-sedation combined with calmatives, and thyroid over-activation in susceptible people.

Drug interactions

• Thyroid medications (levothyroxine, antithyroid drugs): documented effect; can push thyroid hormones up. Monitor or avoid.
• Sedatives/benzodiazepines: additive drowsiness.
• Immunosuppressants: immune-stimulating; can work against the medication.
• Diabetes and blood-pressure drugs: additive glucose- and BP-lowering; mild but real.
• Liver-toxic drugs: theoretical, given the rare liver-injury signal.

Who should not take ashwagandha?

Pregnant women (traditional uterine-stimulant use), hyperthyroid patients, anyone on thyroid medication without monitoring, autoimmune patients on immunosuppressants, people with liver disease, and anyone scheduled for surgery (sedative overlap; stop ~2 weeks prior).

What the authorities say

NCCIH: evidence suggests ashwagandha may reduce stress and anxiety and improve sleep; short-term use up to ~3 months appears safe for most people; long-term safety is unestablished; rare liver injury has been reported; avoid in pregnancy. Memorial Sloan Kettering’s About Herbs database likewise catalogues it for stress with cautions on thyroid, autoimmunity, and sedation. Both positions match what the trial record shows, which is exactly why it’s the most credible adaptogen sold.

What to know about ashwagandha

The strongest cited evidence concerns stress, cortisol, and sleep using standardized extracts, often at 300–600 mg daily. Check the extract name and withanolide concentration; commonly cited preparations include KSM-66 and Sensoril. Studies do not establish indefinite use, and medication and safety cautions still apply.