Ashwagandha: Does It Actually Work?
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What Is Ashwagandha?
Ashwagandha is an adaptogenic herb used in Ayurvedic medicine for thousands of years. Its scientific name is Withania somnifera. It’s one of the most studied herbal supplements available today.
You’ll see it marketed for everything from anxiety to testosterone to muscle growth. Some of those claims hold up. Others don’t.
We analyzed 12 meta-analyses and systematic reviews covering 47 individual studies. Here’s what the data actually shows.
The Evidence, Claim by Claim
The sections below break down each claim with real numbers from published meta-analyses. Every effect size, confidence interval, and study count comes from peer-reviewed research.
Who Should NOT Take Ashwagandha
Don’t take ashwagandha if you have thyroid problems. It can increase thyroid hormone levels, which is dangerous if you’re already on thyroid medication.
Avoid it if you have autoimmune conditions. Ashwagandha stimulates the immune system, which is the opposite of what you want when your immune system is already overactive.
Don’t use it during pregnancy or breastfeeding. There isn’t enough safety data.
Stop taking it at least 2 weeks before surgery. It may interact with anesthesia.
The Bottom Line
Ashwagandha is one of the better-studied herbal supplements. It genuinely works for anxiety and cortisol reduction. There’s decent evidence for strength gains when combined with training.
But don’t buy it for testosterone. The marketing doesn’t match the research, especially for healthy young men. The testosterone studies that showed positive results used infertile or stressed older populations. That’s a very different story than what Instagram influencers are selling.
The Evidence, Claim by Claim
Reduces anxiety ✓ Works
12 studies with about 1,000 people found ashwagandha significantly reduces anxiety scores. The effect is large, but the studies vary a lot in how much benefit they show. KSM-66 and Sensoril extracts at 300-600mg daily both work.
High heterogeneity (I2 = 93.8%) means results vary widely between studies. Some show huge effects, others more modest. The direction is consistent though. It works, but exactly how well varies.
View full statistical analysis
Publication Bias Assessment
| Egger's Test | z = —, p = 0.15 | not formally assessed in primary meta-analysis |
|---|---|---|
| Fail-safe N (Rosenthal) | 450 studies needed to nullify result | |
Subgroup Analysis
| Subgroup | Studies (k) | Effect (g) |
|---|---|---|
| KSM-66 | 6 | -1.72 |
| Sensoril | 3 | -1.2 |
| Other | 3 | -1.35 |
Lowers cortisol ✓ Works
7 studies with about 500 people show ashwagandha lowers blood cortisol levels by about 1.16 ug/dL. That's a meaningful drop in your body's main stress hormone. The consistency across studies is moderate.
Moderate heterogeneity (I2 = 50.9%) is acceptable. One interesting finding: ashwagandha lowers biological cortisol even when people don't always report feeling less stressed on questionnaires.
View full statistical analysis
Publication Bias Assessment
| Egger's Test | z = —, p = 0.3 | no significant asymmetry detected |
|---|
Increases muscle strength ? Maybe
5 studies with about 200 people found ashwagandha provides a medium-sized boost to strength when combined with resistance training. The effect (g = 0.67) is meaningful but based on fewer studies than the anxiety data.
Low heterogeneity is a good sign, meaning the studies agree. But only 5 studies means we need more data. The prediction interval barely crosses zero, so a new study might not find a benefit.
View full statistical analysis
Publication Bias Assessment
| Egger's Test | z = —, p = — | not formally assessed |
|---|
Boosts testosterone ✗ No Evidence
4 small studies with about 220 people show inconsistent results for testosterone. The studies that found increases were done in infertile or stressed men, not healthy young guys. There's no dedicated meta-analysis for this claim.
No published meta-analysis pools ashwagandha's effect on testosterone. The positive studies used infertile or overweight men. Don't expect testosterone changes if you're healthy and young.
View full statistical analysis
Publication Bias Assessment
| Egger's Test | z = —, p = — | insufficient studies for formal testing |
|---|
Dosage Guide
| Effective Range | 300-600mg |
|---|---|
| Optimal Dose | 600mg |
| Best Form | KSM-66 or Sensoril extract |
| Timing | Morning or evening, with food |
| Time to Effect | 2-4 weeks for anxiety effects, 8+ weeks for strength |
| Cycling | 8 weeks on, 2 weeks off recommended |
| Notes | Root extract standardized to withanolides. Raw powder is underdosed. |
Don't Take If
- Thyroid disorders (may worsen hyperthyroidism)
- Autoimmune conditions (immune-stimulating)
- Pregnancy and breastfeeding
- Surgery (stop 2 weeks before)
Drug Interactions
| Medication | Risk | Why |
|---|---|---|
| Thyroid medications | high | May potentiate thyroid hormone effects |
| Benzodiazepines | moderate | Additive sedation |
| Immunosuppressants | moderate | May counteract immunosuppressive effects |
Possible Side Effects
- Mild GI upset at high doses
- Drowsiness (can be beneficial for sleep)
- May increase thyroid hormone levels
What to Buy
Disclosure: Links below are affiliate links. We earn a commission if you buy. We never recommend products that fail our evidence checks.
Nootropics Depot KSM-66 Ashwagandha
KSM-66 extract, third-party tested, correct dose per cap
Nootropics Depot Sensoril Ashwagandha
Sensoril extract, good for evening use (more sedating)
What to Avoid
Unstandardized root powder, need 5+ capsules for effective dose
Frequently Asked Questions
Does ashwagandha work for anxiety?
Yes. 12 randomized controlled trials with about 1,000 people show a large reduction in anxiety scores. Both KSM-66 and Sensoril extracts work at 300-600mg daily.
How long does ashwagandha take to work?
Most studies show anxiety benefits within 2-4 weeks. Strength benefits take 8 or more weeks of consistent use combined with exercise.
Does ashwagandha boost testosterone?
Probably not if you're healthy. The studies showing testosterone increases were done in infertile or stressed older men. Healthy young males shouldn't expect meaningful changes.
Is ashwagandha safe?
Generally safe for most adults at standard doses. Avoid if you have thyroid disorders, autoimmune conditions, or are pregnant. May cause mild stomach upset or drowsiness.
What's the best form of ashwagandha?
KSM-66 or Sensoril extracts have the most research behind them. Avoid unstandardized root powder, which requires much higher doses and has less consistent results.