Ashwagandha

botanical

What is it

Ashwagandha (Withania somnifera) is a small evergreen shrub native to India, the Middle East, and parts of Africa, used in Ayurvedic medicine for over 3,000 years. Its name translates roughly to 'smell of horse,' a reference to both its odor and the traditional belief that it imparts strength.

How it works

Ashwagandha is classified as an adaptogen, a category of plants thought to help the body modulate its response to physical, mental, and emotional stress. Its bioactive compounds, primarily withanolides (especially withaferin A and withanolide D), interact with multiple systems including the hypothalamic-pituitary-adrenal axis, GABAergic neurotransmission, and inflammatory pathways. In human trials, ashwagandha most consistently lowers morning serum cortisol in chronically stressed adults, with reductions of roughly 20 to 30 percent reported in several randomized trials. It appears to enhance GABA receptor signaling, which contributes to its anxiolytic and sleep-promoting effects. Andrological effects (testosterone, sperm quality) are likely mediated through cortisol-related mechanisms; chronic stress suppresses gonadal function, and reducing stress hormones may improve it. Anti-inflammatory and antioxidant effects appear secondary but contribute to broader claims around immune function and recovery.

Evidence for 6 uses

AI-assisted evidence assessment — talk to your doctor before relying on any single supplement.

Stress and anxiety

Grade B

Good evidence

Multiple randomized controlled trials at 300 to 600 mg/day of standardized root extract have shown reductions in perceived stress (PSS scores) and serum cortisol over 8 weeks. A 2019 meta-analysis of 5 RCTs found ashwagandha significantly reduced anxiety compared to placebo. Effects are clearer for chronic, low-level stress than acute panic.

Sleep quality

Grade B

Good evidence

Trials at 300 to 600 mg/day have improved sleep quality scores, sleep onset latency, and subjective restfulness in adults with mild sleep complaints. A 2021 meta-analysis confirmed modest positive effects, particularly in adults with insomnia.

Testosterone and male reproductive health

Grade B

Good evidence

Trials in stressed or infertile men show ashwagandha at 300 to 675 mg/day for 8 to 16 weeks raises serum testosterone by 15 to 22 percent and improves sperm count, motility, and morphology. Effects in non-stressed men with normal testosterone are smaller.

Muscle strength and recovery

Grade C

Moderate evidence

Trials in resistance-trained men at 500 to 1,250 mg/day for 8 to 12 weeks have shown improvements in strength (1RM bench and squat) and muscle size over placebo, sometimes attributed to better stress management and recovery rather than direct anabolic effects. Effect sizes are moderate.

Thyroid function in subclinical hypothyroidism

Grade C

Moderate evidence

A small trial in adults with subclinical hypothyroidism showed 600 mg/day ashwagandha for 8 weeks normalized TSH and increased T3 and T4. This effect is a contraindication in hyperthyroidism and complicates dosing for those on levothyroxine.

Cognitive performance

Grade C

Moderate evidence

Trials in older adults and stressed populations have shown improvements in attention, working memory, and processing speed with 300 to 600 mg/day over 8 weeks. Mechanism likely overlaps with stress reduction.

3 commercial forms

KSM-66 (root extract, 5 percent withanolides)

Standardized water-based extract; used in many positive clinical trials.

One of the most widely studied branded extracts. Typical dose 300 to 600 mg/day.

Sensoril (root and leaf, 10 percent withanolides)

Higher withanolide concentration; used at lower doses.

Standardized alcohol-extract form. Typical dose 125 to 250 mg/day.

Unstandardized ashwagandha root powder

Variable withanolide content; quality control is the main issue.

Traditional Ayurvedic format. Effective dose hard to determine without standardization. Often used at 1 to 3 g/day.

Dosage

There is no standard dose. Most consumer products use 300 to 600 mg per day of root extract, often standardized to a specific withanolide content (typically 1.5 to 5 percent). Common branded extracts include KSM-66 (root only, 5 percent withanolides, used at 300 to 600 mg/day) and Sensoril (root and leaf, 10 percent withanolides, used at 125 to 250 mg/day). Higher doses are used in some andrological trials (up to 675 mg/day) but increased benefits are not clearly demonstrated.

When and how to take it

Ashwagandha is typically taken once or twice daily, with or without food. For stress and anxiety, evening dosing is common because of its calming and sleep-supportive effects. For testosterone and athletic applications, morning and post-workout dosing are popular though there is no strong evidence one timing outperforms another. Effects build over 4 to 8 weeks of consistent use; this is not an acute supplement. Pair with a meal containing some fat for marginally better absorption of fat-soluble withanolides. Cycle off every few months if used long-term, given uncertainty about long-term hepatic safety.

Safety

Ashwagandha is generally well tolerated at typical doses. Common side effects include mild GI upset (nausea, diarrhea, abdominal pain), drowsiness, and rarely allergic skin reactions. Recent reports have raised concerns about rare cases of liver injury (hepatotoxicity), with case reports clustering in 2023 to 2025. The mechanism is unclear and the absolute risk appears low, but the signal has prompted regulators in some countries (Denmark, Nordic countries) to restrict ashwagandha sales. Discontinue and seek medical evaluation if symptoms of liver injury appear (fatigue, jaundice, nausea, abdominal pain). No formal Tolerable Upper Intake Level exists. Long-term safety beyond 12 months is not well characterized. The herb may raise thyroid hormone levels, potentially problematic in hyperthyroidism. Pregnancy is a contraindication; ashwagandha has been associated with abortifacient effects in animal studies.

Who should be cautious

Do not use during pregnancy. Use cautiously while breastfeeding, with autoimmune disease (lupus, RA, MS, Hashimoto's), hyperthyroidism, on thyroid hormone replacement, or with diabetes medications. Coordinate with prescribers if taking sedatives, immunosuppressants, or thyroid drugs. Stop and seek evaluation if symptoms of liver injury appear. Avoid before surgery (anesthesia interaction risk). Children should not use without specialist guidance.

Interactions

Ashwagandha may enhance the effects of sedatives, benzodiazepines, alcohol, and other CNS depressants due to its GABAergic activity. It can lower blood sugar, potentially compounding the effect of diabetes medications. It may raise thyroid hormones, complicating dosing of thyroid replacement (levothyroxine) or worsening hyperthyroidism. May increase the effects of antihypertensives. May reduce the efficacy of immunosuppressants because of its immune-stimulating activity, important for organ transplant recipients and those with autoimmune disease.

Frequently asked questions

How long until ashwagandha works?⌄

Most trials show benefits on stress, sleep, and hormonal markers appearing over 4 to 8 weeks of consistent daily use. It is not an acute supplement; don't expect to feel a difference the first day.

Will ashwagandha really raise my testosterone?⌄

Modestly, and mainly if your testosterone is depressed by chronic stress. Trials show 15 to 22 percent increases in stressed or infertile men. In healthy non-stressed men with normal levels, effects are smaller.

Is ashwagandha safe for my liver?⌄

The vast majority of users have no problem, but case reports of liver injury have accumulated enough that some regulators (Denmark, Iceland) restricted sales. If you have liver disease, take other hepatotoxic drugs, or notice symptoms (fatigue, jaundice, nausea, abdominal pain), stop and seek evaluation.

Can I take ashwagandha every day forever?⌄

Most trials run 8 to 12 weeks. Long-term daily safety beyond 12 months is not well characterized. Many users cycle (8 weeks on, 2 to 4 weeks off) as a conservative approach given the recent liver concerns.

Will ashwagandha make me sleepy during the day?⌄

Most users don't experience daytime drowsiness at typical doses, though some report mild sedation. Evening dosing avoids any issue and may improve sleep quality.

References

  • Wikidata: Withania somnifera — Wikidata link

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Disclaimer: These statements have not been evaluated by the FDA. This page is educational, not a substitute for personalized medical advice. Evidence grades are AI-assisted assessments — talk to your doctor before starting any new supplement, especially if you're pregnant, breastfeeding, on medications, or managing a chronic condition.