Ashwagandha (Withania somnifera)
Ashwagandha is a shrub long used in India's Ayurvedic medicine; most supplements use extracts of its root. In a 2026 analysis of 10 trials, it reduced anxiety compared with placebo, but results varied widely between trials and certainty was rated low to moderate. It may also lower cortisol, a stress hormone.
Ashwagandha (Withania somnifera) is an evergreen shrub grown in tropical and subtropical areas of Asia, Africa and Europe. It has been used as an adaptogen (loosely, something meant to help the body resist or adapt to stress) in India's traditional Ayurvedic and Unani medicine. Most commercial supplements contain extracts of the root, and some contain both root and leaf. Compounds called withanolides are believed to be responsible for many of its proposed effects, though lab studies suggest other compounds may also be involved.
Research & evidence
Strong support Some support Weak or no supportColours show how well the sources back each point. The reason is next to each one.
A 2026 meta-analysis of 10 RCTs (779 participants) found Ashwagandha significantly reduced anxiety (Hamilton Anxiety Rating Scale) compared with placebo. A specific self-reported stress measure (Perceived Stress Scale) showed the same directional trend but did not reach statistical significance in this pooled analysis. Heterogeneity across included trials was high.
Moderate evidenceSome support. Reviewers rated the certainty low
Study details
Luitel et al. 2026: HAM-A (anxiety) Hedges' g=-1.18 (95% CI -2.10 to -0.26, p=0.021, I2=88.2%); PSS (stress) Hedges' g=-1.39 (95% CI -2.97 to 0.19, p=0.0708, I2=95.2%, "a non-significant trend"). Certainty rated "low to moderate due to heterogeneity and imprecision" by the source itself. Results varied widely between trials on every outcome (I2 above 75%). The review was pre-registered on PROSPERO (CRD420261304132) and declares no conflicts of interest and no external funding. The publishing journal (Europasian Journal of Medical Sciences) is not indexed in PubMed/MEDLINE.
Source: Luitel P, K.C. B, Sapkota R, Upreti S. "Efficacy of Ashwagandha (Withania somnifera) on the Management of Anxiety and Stress in Adults: A Systematic Review and Meta-Analysis of Randomized Controlled Trials." Europasian J Med Sci. 2026;8(11):1. View source
Ashwagandha may lower serum cortisol levels.
Moderate evidenceSome support. Reviewers rated the certainty low
Study details
Luitel et al. 2026: serum cortisol Hedges' g=-0.74 (95% CI -1.33 to -0.14, p=0.0246, I2=81.1%). Certainty "low to moderate" per the source's own GRADE-style rating. Based on the same pooled trials as the anxiety finding above (10 RCTs, 779 adults); the meta-analysis didn't analyze chronically stressed adults as a separate subgroup.
Source: Luitel P, K.C. B, Sapkota R, Upreti S. "Efficacy of Ashwagandha (Withania somnifera) on the Management of Anxiety and Stress in Adults: A Systematic Review and Meta-Analysis of Randomized Controlled Trials." Europasian J Med Sci. 2026;8(11):1. View source
Ashwagandha (tested as the standardized KSM-66 extract) has shown a modest, statistically significant testosterone increase (17%) in a small pilot trial of oligospermic (infertile) men, alongside significant improvements in sperm count, motility, and volume. A larger 2026 trial in men with mild-to-moderate erectile dysfunction found significant improvements in semen parameters and sexual-function scores, but testosterone itself did not reach statistical significance in that trial. An independent review flagged several data-quality concerns in that trial (implausible zero-variance lab values, an unverified abstinence protocol, no correction for multiple comparisons).
Limited evidenceSome support. Based on one or a few small trials
Study details
Ambiye et al. 2013 (46 oligospermic men, 90 days, KSM-66): testosterone +17% (4.45 to 5.22 ng/mL, p<0.01); an exploratory pilot with no formal power calculation. Khanna et al. 2026 (76 men, 8 weeks, KSM-66): despite being titled "healthy Men," eligibility required baseline IIEF scores 11-16, i.e., every participant had pre-existing mild-to-moderate erectile dysfunction; "healthy" meant no other diagnosed disease causing it, not symptom-free. This trial's testosterone result was not significant (total T p=0.223, free T p=0.099), while semen parameters (36% ejaculate volume, 38% sperm count, 87% motility) and sexual-function scores improved significantly. An independent critique (Natural Health Research Institute, 2026) documents specific data-quality problems in this trial: a reported standard deviation of exactly 0.00 across 34 people for multiple lab markers ("physiologically impossible"), a standard deviation exceeding its own mean for sperm concentration ("mathematically impossible for a non-negative variable"), an unverified abstinence window, an 8-week duration short of a full spermatogenic cycle (~74 days), zero dropouts across 76 participants called "unexplained and arguably implausible," and says the study's Discussion over-interprets its null testosterone finding. Both trials tested the same commercial extract (KSM-66, Ixoreal Biomed). Ambiye et al. doesn't address funding; Khanna et al. states none was received.
Source: Ambiye VR, Langade D, Dongre S, et al. "Clinical Evaluation of the Spermatogenic Activity of the Root Extract of Ashwagandha in Oligospermic Males: A Pilot Study." Evid Based Complement Alternat Med. 2013;2013:571420; Khanna A, Khanna M, Panchal P. "Efficacy and safety of ashwagandha root extract on sexual health in healthy Men." Front Reprod Health. 2026;8:1774098; independent critique: Natural Health Research Institute, "Ashwagandha Root Extract (KSM-66) and Male Sexual Health." July 1, 2026. View source
Dosage
| Form | Amount |
|---|---|
| Any form | There's no standard recommended dose: NIH says it's difficult to identify specific extracts or recommended amounts, and MSK gives no dose. In stress and anxiety trials, doses ranged from 240 to 1,250 mg a day of extract, or 12,000 mg a day of whole root granules. An international taskforce (WFSBP and CANMAT, 2022) provisionally recommended 300 to 600 mg a day of root extract standardized to 5% withanolides for generalized anxiety disorder. |
Side effects
The most common side effects, such as loose stools, nausea and drowsiness, are usually mild. Don't drive until you know how it affects you. In a few reported cases it has been linked to liver injury, so stop and see a doctor if your skin or eyes turn yellow.
Well documented Reported (case reports, anecdotal or one study) None reportedThe circle shows how well documented an effect is, not how serious it is. A rarely reported effect can still be serious, so always read ‘When to stop’.
| Effect | Frequency | When to stop |
|---|---|---|
| DrowsinessWell documentedListed plainly by NIH, MSK or LiverTox | Common; usually mild | Don't drive or do anything that needs you alert until you know how it affects you. Stop and talk to a doctor if it's severe. |
| Loose stools or diarrhea, nausea, stomach irritationWell documentedListed plainly by NIH, MSK or LiverTox | Common; usually mild | Stop and talk to a doctor if it persists. |
| HeadacheWell documentedListed plainly by NIH, MSK or LiverTox | Not stated | Stop and talk to a doctor if it persists. |
| Liver injury (signs include yellowing of the skin or eyes, itching, nausea and tiredness)ReportedCase reports only | Rare; a few case reports | Stop taking it and see a doctor right away if you notice any of these. |
Safety & interactions
Safety
Ashwagandha appears to be well tolerated for up to about 3 months, but its long-term safety isn't known. Common side effects, such as loose stools, nausea and drowsiness, are usually mild. There are a few reports of more serious side effects, including liver injury, with signs such as jaundice (yellowing of the skin or eyes), itching, nausea and tiredness. Ashwagandha might also affect thyroid function and might raise testosterone levels.
Contraindications
Don't use ashwagandha if you're pregnant: MSK says it may increase the risk of miscarriage, and NIH notes that some experts advise against it in pregnancy. France's food safety agency (ANSES) recommends against it for people who are pregnant or breastfeeding and people with endocrine (hormone) disorders. Talk with your doctor first if you have hormone-sensitive prostate cancer, because ashwagandha may increase testosterone levels. MSK also says it may trigger or worsen autoimmune diseases. If you take sedatives, thyroid medication or immunosuppressants, see Drug interactions.
Drug interactions
NIH ODS lists sedatives among the medications ashwagandha might interact with, without giving a reason. MSK reports preclinical evidence that ashwagandha has sedative and GABA-related effects that may add to those of anticonvulsants, barbiturates and benzodiazepines. MSK says the clinical relevance has yet to be determined, and advises that people taking these drugs should likely avoid ashwagandha. MSK's patient page also says ashwagandha may increase the drowsiness effects of some prescription medications.
Ashwagandha can raise thyroid hormone levels. In a small trial in people with subclinical hypothyroidism, it lowered TSH and raised T3 and T4, and there are case reports of thyrotoxicosis that resolved after stopping it (doses weren't stated in two of the three cases; the third involved a notably high dose of 1,950 mg/day). Combining ashwagandha with thyroid hormone medication like levothyroxine could push levels too high. That specific risk is inferred from the hormone effect rather than studied directly.
NIH ODS lists immunosuppressants among the medications ashwagandha might interact with, without giving a reason. MSK reports a case of kidney transplant rejection associated with ashwagandha use in a 69-year-old patient, who lost the graft and needed ongoing dialysis. MSK doesn't say ashwagandha caused the rejection, and doesn't name the patient's immunosuppressant. MSK also says ashwagandha may trigger or worsen autoimmune diseases. If you've had a transplant or take immunosuppressants, don't take ashwagandha unless your care team approves.
NIH ODS lists antidiabetes medications among the medications ashwagandha might interact with, but doesn't give a reason or name specific drugs.
NIH ODS lists blood pressure medications (antihypertensives) among the medications ashwagandha might interact with, but doesn't give a reason or name specific drugs.
In lab studies, ashwagandha moderately increased the activity of CYP3A4, an enzyme the body uses to break down drugs, which can change the levels of drugs metabolized by this enzyme. MSK says the clinical relevance is not known. If you take a prescription medication, ask your pharmacist whether CYP3A4 breaks it down.
In lab studies, ashwagandha decreased the activity of CYP2B6, an enzyme the body uses to break down drugs, which may change the levels of drugs metabolized by this enzyme. MSK says the clinical relevance has yet to be determined. If you take a prescription medication, ask your pharmacist whether CYP2B6 breaks it down.
Established: stated plainly by an authoritative source. Documented: supported by case reports or trial data. Theoretical: based on mechanism, animal data, or a cautious listing. Always check with your pharmacist or prescriber.