We cover the side effects seen in trials, the rare cases of liver injury, ashwagandha's effects on thyroid and testosterone, and who should see a doctor before taking it.
Up to about three months, most men tolerate ashwagandha well, and the usual complaints are stomach upset and drowsiness. Raised thyroid hormone levels and rare liver injury are rarer but more serious. Talk to a doctor first if you have a thyroid, liver or autoimmune condition or hormone-sensitive prostate cancer, or if you take sedatives, thyroid, diabetes, blood pressure or immunosuppressant drugs.
Clinical trials found that few men taking ashwagandha had any problems. According to the NIH Office of Dietary Supplements (ODS), it seems well tolerated for up to about three months, and side effects are mostly mild. NCCIH names the same two main ones:
Dose matters here, and taking it with food, cutting the dose or shifting it to the evening often helps. We go through this in when to take ashwagandha.
Duration is the main limit. NCCIH notes that long-term safety information is lacking, and most trials lasted 6 to 12 weeks. Using it for months or years with no break goes beyond what has been studied.
Men are most likely to overlook the effect on the thyroid, because ashwagandha can raise thyroid hormone levels without any obvious early symptoms.
Here is what the ODS fact sheet reports. Three men in one small study took 500 mg a day of a root and leaf extract for 8 weeks and had small rises in T4. Another trial, of 50 people with subclinical hypothyroidism, gave 300 mg twice daily for 8 weeks, and TSH fell while T3 and T4 rose compared with placebo. Thyrotoxicosis (an overactive thyroid state) has also been reported in case reports, and it resolved once the supplement was stopped.
If your thyroid is sluggish, that might sound useful, but the effect cuts both ways. Levothyroxine or another thyroid medication plus ashwagandha could push your levels too high, and an overactive thyroid could get worse. NCCIH does not recommend it for people with thyroid disorders. A racing heart, shakiness, heat intolerance, sweating or unexplained weight loss are signs to get your levels checked.
This is the most serious risk. NIH's LiverTox database rates ashwagandha a likely cause of clinically apparent liver injury, while stating that it happens rarely. Reports date from 2017, and reviews have tallied roughly 9 to 23 published cases.
Per LiverTox, symptoms commonly begin between 2 and 12 weeks after starting. Jaundice (yellow skin or eyes) and itching are typical. Mild to moderate cases made up most of the reports, and these cleared within 1 to 4 months once the supplement was stopped. Fatal cases and rare cases needing a liver transplant have been described too, mostly in people who already had liver disease or cirrhosis. Five cases in adults aged 21 to 62, three of them men, taking 450 to 1,350 mg a day are listed by the ODS.
Why it happens isn't known. Withanolides are suspected, and mislabeled or contaminated products are a recognized problem, though some cases involved products that tested clean. Anyone with cirrhosis or advanced liver disease should avoid ashwagandha. Stop right away if your skin or eyes turn yellow, or if you notice dark urine, pale stools, itching or unusual tiredness.
Some small trials found that ashwagandha raised testosterone, which is part of why men like it. A 2019 crossover study followed 57 overweight men aged 40 to 70, and their salivary testosterone climbed 14.7% more on ashwagandha than on placebo, though fatigue and vigor did not improve more than placebo. A 2015 trial of young men doing strength training also saw a bigger testosterone rise in the KSM-66 group than in the placebo group. Both trials were small, and the extract in the second was supplied by its manufacturers.
Because of this hormonal effect, NCCIH and the ODS say ashwagandha may be unsafe for men with hormone-sensitive prostate cancer. Anyone who has prostate cancer, is being monitored for it, or takes hormone therapy should get their oncologist's approval before using it.
The same effect explains why testosterone booster formulas often contain it. Read the label if you use one, so you don't double up with a separate ashwagandha supplement. One such combination product is covered in our Testosil side effects article.
NCCIH and the ODS name the interactions below. None has been studied well, so each one is a reason to ask your doctor or pharmacist before you start.
| Medication type | What the concern is |
|---|---|
| Sedatives and sleep aids (benzodiazepines, sleeping pills, some anti-anxiety drugs) | May add to drowsiness |
| Thyroid hormone (levothyroxine) | May push thyroid hormone levels higher |
| Diabetes medications | May alter blood sugar control |
| Blood pressure medications | May alter blood pressure control |
| Immunosuppressants (for transplants or autoimmune disease) | Named as a possible interaction; don't combine without your doctor's approval |
| Anti-seizure medications | NCCIH names it as a possible interaction |
Plenty of men add ashwagandha for stress while already taking a blood pressure drug, a statin, a diabetes medicine or a sleep aid. Stacking them is where five minutes with a pharmacist pays off.
Outside the US, regulators have been stricter. The Technical University of Denmark issued a risk assessment in 2020 that raised concerns about pregnancy, thyroid and sex hormone effects, and the ODS reports that Denmark then banned ashwagandha in supplements in 2023. France's food safety agency ANSES advised in 2024 that certain groups, among them people with hormonal disorders, avoid it. Trade press reports that the Netherlands advised against use in 2024 and that the UK Food Standards Agency opened a call for evidence that same year. The industry disputes parts of the Danish assessment. It stays legal as a dietary supplement in the US, but these reviews show that safety data is still thin.
Our piece on ashwagandha for cortisol reduction covers the benefits if stress and cortisol are your reason for taking it, and the KSM-66 ashwagandha guide looks at the most widely studied extract.
Over the 2 to 3 months that trials have covered, healthy men mostly report mild effects, chiefly stomach upset and drowsiness. Rarer and more serious risks deserve attention: changes in thyroid hormone, rare liver injury, and a possible testosterone effect that rules it out for men with hormone-sensitive prostate cancer. Ask your doctor first if you have a thyroid, liver or autoimmune condition or take sedatives, thyroid, diabetes, blood pressure or immunosuppressant drugs. Follow the label dose, take breaks rather than using it indefinitely, and stop at the first sign of yellow skin or eyes.