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Can I take ashwagandha with levothyroxine?

Only with your prescriber's OK: NIH's NCCIH says ashwagandha is not recommended for people with thyroid disorders. The interaction itself is theoretical only, since nobody has studied or reported the two taken together. Still, in an 8-week trial in 50 adults with a mildly underactive thyroid, ashwagandha moved TSH, T3 and T4 toward normal, and case reports describe an overactive thyroid in people taking it. Plan a thyroid recheck with your prescriber.

How well documented: Theoretical only. No study or case report in people for this pair: the concern comes from how the two work.

Last reviewed

How we grade evidenceEditorial policy

What's known

  • Theory. Levothyroxine replaces missing thyroid hormone, and its dose is set by blood tests. Its label says it has a narrow therapeutic index (a small gap between too little and too much). Too much causes signs of an overactive thyroid, such as a fast or irregular heartbeat, tremor, trouble sleeping and weight loss. If ashwagandha adds its own push, the two could add up. No study or case report of the pair was found. (Synthroid label)
  • Ashwagandha alone. In one 8-week trial, 50 adults aged 18 to 50 with subclinical hypothyroidism (a high TSH without clear symptoms) took 600 mg of ashwagandha root extract a day or a placebo. TSH (the brain's signal to the thyroid) and the thyroid hormones T3 and T4 moved toward normal with ashwagandha compared with placebo, in a small trial at one hospital. In a trial in bipolar disorder, T4 rose in all 3 people on ashwagandha whose thyroid tests were flagged. (Sharma 2018, Gannon 2014)
  • Case reports. A healthy 32-year-old woman on no other medicines developed thyrotoxicosis (too much thyroid hormone) after raising her ashwagandha dose. A 47-year-old man developed painless thyroiditis two months after starting it. A 73-year-old woman who had swapped her levothyroxine for ashwagandha two years earlier was found to have a racing heart (supraventricular tachycardia) and a TSH far below normal. All three got better after stopping the herb. None was on levothyroxine at the time. (van der Hooft 2005, Hayashi 2024, Kamal 2022)
  • Who is at risk. NCCIH says ashwagandha is not recommended for people with thyroid disorders, lists thyroid hormone medicines among those it might interact with, and advises avoiding it in pregnancy and while breastfeeding. Rare liver injury has been reported, usually 2 to 12 weeks after starting, with jaundice (yellow skin or eyes) and itching. (NCCIH, LiverTox)

What to do

  • Talk to your prescriber or pharmacist before you start ashwagandha. If you go ahead, ask whether your TSH should be rechecked, since levothyroxine is adjusted by blood tests. Tell them if you later quit the herb, too.
  • Get medical help for a racing or irregular heartbeat, chest pain, tremor, heat intolerance, weight loss you can't explain, or yellow skin or eyes.
  • Don't use ashwagandha in place of your thyroid medicine. In one case report, a woman who did this became seriously ill.
  • Don't stop or change a prescribed medicine on your own.
  • If you're pregnant, planning a pregnancy or breastfeeding, ask your doctor or midwife first.

Sources

  1. US National Library of Medicine. Synthroid (levothyroxine sodium) tablets: prescribing information. DailyMed, revised 02/2024. DailyMed
  2. Sharma AK, et al. Efficacy and Safety of Ashwagandha Root Extract in Subclinical Hypothyroid Patients: A Double-Blind, Randomized Placebo-Controlled Trial. J Altern Complement Med. 2018. PubMed 28829155 · doi:10.1089/acm.2017.0183
  3. Gannon JM, et al. Subtle changes in thyroid indices during a placebo-controlled study of an extract of Withania somnifera in persons with bipolar disorder. J Ayurveda Integr Med. 2014. PubMed 25624699 · doi:10.4103/0975-9476.146566
  4. van der Hooft CS, et al. [Thyrotoxicosis following the use of ashwagandha]. Ned Tijdschr Geneeskd. 2005. PubMed 16355578
  5. Hayashi M, et al. Painless Thyroiditis by Withania somnifera (Ashwagandha). Cureus. 2024. PubMed 38559552 · doi:10.7759/cureus.55352
  6. Kamal HI, et al. Ashwagandha as a Unique Cause of Thyrotoxicosis Presenting With Supraventricular Tachycardia. Cureus. 2022. PubMed 35475098 · doi:10.7759/cureus.23494
  7. National Center for Complementary and Integrative Health. Ashwagandha. Last updated March 2023. NCCIH
  8. LiverTox: Clinical and Research Information on Drug-Induced Liver Injury. Ashwagandha. NIDDK, updated 3 December 2024. NCBI Bookshelf