Ashwagandha and Thyroid: A Hidden Risk

Ashwagandha (Withania somnifera) is one of the most popular adaptogens on the market, marketed for stress, cortisol, energy, and general wellbeing. It has some real clinical support for stress and sleep at standardized doses. But there is a safety consideration that almost no consumer-facing marketing mentions: ashwagandha can raise thyroid hormone levels and, in vulnerable people, push them into hyperthyroidism or even thyrotoxicosis.

The Mechanism

Animal studies and at least one randomized controlled trial show that W. somnifera root extract increases serum T3 (triiodothyronine) and T4 (thyroxine) and lowers TSH. In a 2018 randomized, double-blind, placebo-controlled trial in adults with subclinical hypothyroidism (Sharma 2018, J Altern Complement Med), 600 mg/day of standardized ashwagandha root extract for 8 weeks raised mean T3 and T4 and reduced TSH compared with placebo. In a previous mouse study by Panda and Kar, the root extract increased serum T3 and T4 levels in female mice. The pattern across these studies is consistent with stimulation of thyroid hormone production rather than a peripheral effect.

Who Is at Risk

People with pre-existing hyperthyroidism or Graves’ disease have the most to lose: a further bump in T3 and T4 in someone who is already over-active can worsen palpitations, weight loss, heat intolerance, and anxiety, and in severe cases can contribute to thyroid storm. There are published case reports of thyrotoxicosis associated with ashwagandha supplementation in people without a prior thyroid diagnosis (van der Hooft 2005; LiverTox 2020), consistent with subclinical disease that became clinical once thyroid output was nudged up. People on levothyroxine for hypothyroidism are in a different but related position: a supplement that nudges endogenous thyroid output can cause symptoms of over-replacement and prompt unnecessary medication changes.

Beyond the thyroid signal, the LiverTox database and a growing number of case reports also describe rare ashwagandha-associated liver injury, typically appearing within 1 to 5 months of starting supplementation, often presenting as cholestatic or mixed hepatitis that resolves on stopping. This is a separate but parallel reason to take supposedly inert "wellness" doses seriously.

Practical Guidance

Anyone with a thyroid condition — diagnosed hyperthyroidism, hypothyroidism on medication, Hashimoto’s thyroiditis, or a strong family history of thyroid disease — should discuss ashwagandha use with a clinician before starting. New or worsening unexplained weight loss, palpitations, heat intolerance, anxiety, or tremor in anyone taking ashwagandha is reason to stop and check thyroid labs. New jaundice, dark urine, right-upper-quadrant pain, or unexplained fatigue should trigger checking liver enzymes. For healthy adults with no thyroid or liver disease and no relevant medications, short-term use at studied doses (typically 300 to 600 mg/day of a standardized root extract) appears generally well tolerated, but the thyroid and liver signals are real and worth respecting.