The side effects reported in trials, the rare liver injury cases, how ashwagandha affects thyroid and testosterone, and who should talk to a doctor first.
Most men tolerate ashwagandha well for up to about three months, with stomach upset and drowsiness the most common side effects. Less common but more serious risks include raised thyroid hormone levels and rare liver injury. Men with thyroid, liver or autoimmune conditions or hormone-sensitive prostate cancer, and those taking sedatives, thyroid, diabetes, blood pressure or immunosuppressant drugs, should talk to a doctor first.
Most men who take ashwagandha in clinical trials report few or no problems. The NIH Office of Dietary Supplements (ODS) says it appears to be well tolerated for up to about three months, with mostly mild side effects. NCCIH lists the same main ones:
These tend to be dose-related and often settle by taking it with food, lowering the dose, or moving it to the evening. Our guide to the best time to take ashwagandha covers that in more detail.
The key limit is time. Most trials ran 6 to 12 weeks, and NCCIH says there is not enough information about long-term safety. Taking it for months or years without a break is outside what has been studied.
Ashwagandha can raise thyroid hormone levels, and that is the side effect men are most likely to miss because it has no obvious early symptoms.
The ODS fact sheet summarizes the evidence. In one small study, three men taking 500 mg a day of a root and leaf extract for 8 weeks had small rises in T4. In a trial of 50 people with subclinical hypothyroidism, 300 mg twice daily for 8 weeks lowered TSH and raised T3 and T4 compared with placebo. There are also case reports of thyrotoxicosis (an overactive thyroid state), which resolved after the supplement was stopped.
For someone with a sluggish thyroid, that sounds like it could help, but it cuts both ways. If you take levothyroxine or another thyroid medication, ashwagandha could push your levels too high. If you have an overactive thyroid, it could make it worse. NCCIH says ashwagandha is not recommended for people with thyroid disorders. Watch for a racing heart, shakiness, heat intolerance, sweating or unexplained weight loss, and get your levels checked if they appear.
This is the most serious risk. The NIH LiverTox database rates ashwagandha as a likely cause of clinically apparent liver injury, though it says this occurs rarely. Cases have been reported since 2017, and reviews have counted from about 9 to 23 published cases.
According to LiverTox, injury typically appears 2 to 12 weeks after starting, usually with jaundice (yellow skin or eyes) and itching. Most cases were mild to moderate and resolved within 1 to 4 months of stopping. However, fatal cases and rare cases needing a liver transplant have been described, mostly in people who already had liver disease or cirrhosis. The ODS lists five cases in adults aged 21 to 62, three of them men, on 450 to 1,350 mg a day.
Nobody knows exactly why it happens. Withanolides are suspected, and mislabeled or contaminated products are a known problem, though some cases involved products that tested clean. Avoid ashwagandha if you have cirrhosis or advanced liver disease, and stop it right away if you notice yellowing skin or eyes, dark urine, pale stools, itching or unusual tiredness.
Ashwagandha is popular with men partly because some small trials found it raised testosterone. In a 2019 crossover study of 57 overweight men aged 40 to 70, salivary testosterone rose 14.7% more on ashwagandha than on placebo, though fatigue and vigor did not improve more than placebo. In a 2015 trial of young men doing strength training, the KSM-66 group had a larger testosterone rise than the placebo group. Both trials were small and the second was supplied with the extract by its manufacturers.
That hormonal effect is why NCCIH and the ODS say ashwagandha may not be safe for men with hormone-sensitive prostate cancer. If you have prostate cancer, are being monitored for it, or take hormone therapy, do not use it without your oncologist's approval.
This is also why ashwagandha turns up in testosterone booster formulas. If you take one, check the label so you do not double up with a separate ashwagandha supplement. Our article on Testosil side effects looks at one such combination product.
NCCIH and the ODS list these possible interactions. None of them has been well studied, so treat each as a reason to ask your doctor or pharmacist first.
| Medication type | Why it matters |
|---|---|
| Sedatives and sleep aids (benzodiazepines, sleeping pills, some anti-anxiety drugs) | Ashwagandha may add to drowsiness |
| Thyroid hormone (levothyroxine) | Ashwagandha may raise thyroid hormone levels |
| Diabetes medications | Could change blood sugar control |
| Blood pressure medications | Could change blood pressure control |
| Immunosuppressants (for transplants or autoimmune disease) | Listed as a possible interaction; avoid combining without your doctor's approval |
| Anti-seizure medications | Listed by NCCIH as a possible interaction |
Men often add ashwagandha for stress while already on a blood pressure drug, a statin, a diabetes medicine or a sleep aid. That stacking is exactly where a pharmacist check is worth five minutes.
Regulators outside the US have taken a harder look. After a 2020 Technical University of Denmark risk assessment raised concerns about pregnancy, thyroid and sex hormone effects, Denmark banned ashwagandha in supplements in 2023, according to the ODS. France's food safety agency ANSES advised in 2024 that certain groups, including people with hormonal disorders, avoid it. Trade press reports that the Netherlands advised against use in 2024 and the UK Food Standards Agency opened a call for evidence the same year. The industry disputes parts of the Danish assessment. In the US it remains legal as a dietary supplement, but these reviews are a reminder that safety data is still thin.
If you are mainly taking it for cortisol and stress, our look at ashwagandha for cortisol reduction covers the benefit side, and our KSM-66 ashwagandha guide covers the most widely studied extract.
For most healthy men, ashwagandha's side effects are mild, mainly stomach upset and drowsiness, over the 2 to 3 months that trials have tested. The risks that matter are less common but more serious: thyroid hormone changes, rare liver injury, and a possible testosterone effect that rules it out for men with hormone-sensitive prostate cancer. Talk to your doctor first if you have a thyroid, liver or autoimmune condition, or take sedatives, thyroid, diabetes, blood pressure or immunosuppressant drugs. Stick to the label dose, take breaks rather than using it indefinitely, and stop at the first sign of yellowing skin or eyes.