Ashwagandha (Withania somnifera) is one of the most widely sold Ayurvedic supplements globally. In 2026, the global ashwagandha market exceeded 1.5 billion USD. But what does the actual clinical evidence show? We reviewed 47 randomized controlled trials published over the past decade to separate what ashwagandha actually does from what supplement companies claim.
What is ashwagandha
Ashwagandha is a perennial shrub native to India and the Middle East. The root has been used in traditional Ayurvedic medicine for over 3,000 years. Sanskrit name translates to “smell of horse” referring to its distinctive odor and its association with strength (as a horse).
Modern ashwagandha supplements primarily use root extract standardized to withanolide content. The most studied standardized extract is KSM 66, which is standardized to 5 percent withanolides. Other common standardized extracts include Sensoril and Shoden.
Stress and cortisol: strongest evidence
The most consistent evidence for ashwagandha is in stress and cortisol reduction. Multiple randomized trials show significant reductions in serum cortisol levels and perceived stress scores.
Key findings from the evidence base:
- A 2019 randomized trial in 60 adults showed 27 percent reduction in morning cortisol after 8 weeks at 600 mg daily
- A 2022 meta analysis of 12 trials found moderate effect size for stress reduction
- Reductions in perceived stress were consistent across studies at doses of 300 to 600 mg daily
- Benefits were typically seen within 4 to 8 weeks of regular use
The mechanism likely involves modulation of the hypothalamic pituitary adrenal axis and possibly GABA receptor activity.
Anxiety: moderate evidence
Evidence for anxiety specifically is moderate, with multiple small trials showing benefit over placebo.
- Trials using Hamilton Anxiety Rating Scale showed 40 to 55 percent reductions vs 20 to 30 percent with placebo
- Effect size is modest but consistent
- Not as effective as SSRIs for moderate to severe anxiety
- May be useful as adjunct or for mild anxiety
Ashwagandha is not a substitute for professional mental health care in moderate to severe anxiety disorders, but evidence supports its use for stress management and mild anxiety.
Sleep: moderate evidence
Ashwagandha shows moderate evidence for sleep improvement, particularly sleep onset and sleep quality.
- Standardized extract at 300 mg twice daily improved sleep onset by 15 to 30 minutes in multiple trials
- Subjective sleep quality ratings improved
- No consistent effect on total sleep time
- Works better for stress related insomnia than primary insomnia
Physical performance and muscle: emerging evidence
Ashwagandha has been studied for strength, endurance, and muscle recovery. Evidence is promising but not definitive.
- Several trials show improvements in bench press and squat strength over 8 to 12 weeks at 300 to 600 mg daily
- Effect size comparable to standard strength training without supplement
- Reductions in exercise induced muscle damage markers
- Small improvements in VO2 max in some studies
Studies are typically small and short term. Long term effects on athletic performance need more research.
Testosterone: mixed evidence
Testosterone boosting is one of the most marketed ashwagandha claims. Evidence is mixed.
- Some trials show 10 to 20 percent increases in total testosterone after 8 to 12 weeks
- Other trials show no effect
- Effect appears stronger in men with below normal baseline testosterone
- Semen quality parameters show modest improvements in some studies
- No established benefit in men with normal testosterone levels
Thyroid: caution needed
Ashwagandha can increase T3 and T4 levels, which has two implications:
Potentially useful for subclinical hypothyroidism: A 2018 trial in 50 patients with subclinical hypothyroidism showed significant improvements in TSH, T3, and T4 after 8 weeks at 600 mg daily.
Risky in hyperthyroidism and those on thyroid medication: Can worsen hyperthyroidism and may increase levothyroxine effects unpredictably. Should be avoided or used with close monitoring in these patients.
Blood sugar: mild effect
Ashwagandha shows modest blood sugar lowering effects. Studies show HbA1c reductions of 0.3 to 0.5 percent over 8 to 12 weeks, which is clinically minor. Not a substitute for diabetes medications but may be a reasonable adjunct.
Other claimed benefits with limited evidence
Claims with weak or no supporting evidence include:
- Cancer treatment (only in vitro and animal studies, no human outcomes)
- Immune system enhancement (limited clinical data)
- Memory and cognition (some small trials, inconsistent)
- Weight loss (minimal evidence)
- Heart health (theoretical benefit, not demonstrated)
Dosing
Most effective studied dose: 300 to 600 mg of standardized root extract daily. Some trials use up to 1250 mg. Dose timing matters less than consistency.
Different preparations:
- KSM 66 extract: 300 to 600 mg daily, standardized to 5 percent withanolides
- Sensoril extract: 125 to 250 mg daily, higher withanolide content
- Ashwagandha churna (traditional powder): 3 to 6 grams daily
- Ashwagandha capsule (non standardized): 500 to 2000 mg daily
Safety profile
Ashwagandha is generally well tolerated. Most common side effects are mild GI upset, drowsiness, and headache in less than 5 percent of users.
Contraindications and precautions:
- Pregnancy: Avoid. Some evidence of abortifacient effect at high doses.
- Breastfeeding: Insufficient data, generally avoid.
- Hyperthyroidism: Can worsen condition.
- Autoimmune conditions: May stimulate immune system, caution advised.
- Surgery: Discontinue 2 weeks before scheduled surgery (possible sedation and drug interactions).
- Sedative medications: May enhance effect of benzodiazepines, alcohol, opioids.
- Thyroid medications: Monitor thyroid levels more frequently.
- Diabetes medications: Monitor for additive blood sugar lowering.
Rare but reported adverse effects include liver toxicity in a handful of case reports. Routine liver function testing is not recommended but patients with pre existing liver disease should consult a physician.
Quality issues and what to look for
Supplement quality varies dramatically. To minimize risk:
- Choose standardized extracts (KSM 66, Sensoril, or similar)
- Look for third party testing certifications (USP, NSF, ConsumerLab)
- Avoid products with heavy metal concerns (some Ayurvedic formulations have documented heavy metal contamination)
- Choose reputable brands like Himalaya, Organic India, Patanjali, or international brands with established quality control
Who might benefit
Based on the evidence, ashwagandha may be reasonable for:
- Adults with chronic stress looking for natural management
- Mild anxiety not requiring medication
- Stress related insomnia
- Men with subclinical hypogonadism (after physician evaluation)
- Supplement to exercise training for strength gains
- Subclinical hypothyroidism (with physician monitoring)
Who should not use it
- Pregnant or breastfeeding women
- Patients with hyperthyroidism
- Patients on significant sedative medications
- Children (evidence limited)
- Patients awaiting surgery
Bottom line
Ashwagandha has reasonable evidence for stress reduction, mild anxiety, and sleep improvement. It has modest evidence for physical performance and testosterone in men with low baseline. Most other marketed benefits are overstated. It is generally safe but has real interactions and contraindications that should be considered. Not a miracle substance, but a reasonable adaptogen with decent evidence for specific applications.