Ashwagandha Side Effects: Thyroid, Liver & Who Should Avoid It

By Erin Rose · Published August 21, 2026 · Reviewed against primary sources · Methodology · About Us

Informational summary of published research — not medical advice. Do not use in pregnancy or breastfeeding. If you take thyroid medication, an immunosuppressant, or have liver disease, talk to a doctor before starting ashwagandha.

Looking for a tested product? See our best ashwagandha ranked by cost per studied dose, which also covers these safety details →

The common, mild tier: GI upset and drowsiness

The side effects you're actually likely to notice are unglamorous. A 2020 systematic review pooled 30 human clinical trials of ashwagandha root extract and found the most commonly reported adverse events — occurring in more than 5% of participants — were somnolence (sleepiness), epigastric discomfort, and loose stools (Tandon & Yadav 2020, PMID: 32201301). Less common effects reported across the same trials included dizziness, nasal congestion, decreased appetite, nausea, constipation, dry mouth, and mild weight gain. Critically, the same review found no serious adverse events and no meaningful changes to blood counts or standard biochemistry across those 30 trials.

Two practical fixes come up repeatedly in how the trials were run and in general clinical advice: take it with food to reduce GI upset, and take it in the evening if it makes you drowsy — a useful trait if sleep is your goal, less useful if you were hoping to take it in the morning.

Thyroid hormone: a real, measurable effect

For someone with an underactive thyroid, that shift can be the point. For someone with hyperthyroidism, or who is already on thyroid medication and correctly dosed, the same effect is a caution — ashwagandha could push levels further than intended. Coordinate with a doctor and expect thyroid labs to be monitored if you take both.

Immune stimulation: why it matters for autoimmune disease

Ashwagandha is traditionally used in Ayurveda as an "immunomodulator," and part of that reputation is a genuine immune-stimulating effect. That's the opposite of what you want if you have an autoimmune condition (where the immune system is already overactive against the body's own tissue) or if you take an immunosuppressant medication, where the drug's entire job is to dial immune activity down. NIH's NCCIH lists autoimmune disease as a caution for this reason, and advises stopping ashwagandha before scheduled surgery (NCCIH, Ashwagandha: Usefulness and Safety). If you have an autoimmune condition or take an immunosuppressant, treat this as a talk-to-your-doctor-first situation, not a guess.

Liver injury: rare, but real enough to track

Published case reports — not the controlled trials above — describe a rare, cholestatic pattern of ashwagandha-associated liver injury that typically shows up 2-12 weeks after starting and resolves after stopping, though rare severe cases have occurred. NIH's LiverTox database classifies ashwagandha as an uncommon but likely cause of clinically apparent liver injury. This is a real signal, and people with existing liver disease should avoid ashwagandha — but a case-report signal isn't a rate, and it shouldn't be conflated with the common, mild GI/drowsiness effects above. We've kept the full case-by-case evidence, the warning signs, and what FDA adverse-event data does and doesn't show on its own page: Ashwagandha and liver safety: what the evidence shows.

Pregnancy: a hard no

NIH's NCCIH advises against using ashwagandha during pregnancy because of a possible risk of miscarriage, and also advises against use while breastfeeding, where safety data is lacking (NCCIH, Ashwagandha: Usefulness and Safety). Unlike the thyroid or immune cautions above, which are about coordinating with a doctor, this one is not a dose question or a "check with your doctor first" — treat it as a contraindication.

Ashwagandha side effects at a glance

Compare Ashwagandha Products by Cost Per Studied Dose

If you're ready to buy, here's how the ashwagandha products we track and verify compare on cost per studied dose.

Frequently asked questions

Related guides

• Ashwagandha Liver Safety — the case reports and FDA adverse-event data, in full
• Ashwagandha Dosage Guide — dose by goal, plus the safety section
• Best Ashwagandha Overall — Verified picks, ranked by cost per studied dose
• Best Ashwagandha for Anxiety & Stress — its best-evidenced use
• All Ashwagandha Guides

Sources