Ashwagandha (Withania somnifera) has demonstrated thyroid-stimulating properties in multiple clinical studies, which creates an important interaction consideration for anyone taking thyroid medication. Research published in the Journal of Alternative and Complementary Medicine showed that ashwagandha supplementation significantly increased serum T4 and T3 levels in subclinical hypothyroid patients. This thyroid-boosting effect, while potentially beneficial for some, can be problematic when combined with thyroid hormone replacement medications like levothyroxine (Synthroid) or liothyronine (Cytomel).
For individuals on thyroid medication, adding ashwagandha without adjusting their prescription dose could lead to hyperthyroid symptoms including anxiety, rapid heart rate, tremors, weight loss, and insomnia. Conversely, for those with hyperthyroidism or Graves' disease, ashwagandha's thyroid-stimulating effects could worsen their condition. The interaction is not immediately dangerous in most cases, but it can gradually shift thyroid levels outside the therapeutic range that your doctor has carefully optimized.
If you are interested in ashwagandha's stress-relieving and adaptogenic benefits while on thyroid medication, work with your endocrinologist to monitor thyroid function with periodic TSH and free T3/T4 blood tests. Your thyroid medication dose may need adjustment. Never start or stop ashwagandha while on thyroid medication without informing your prescribing physician.
How They Interact
Ashwagandha's withanolides stimulate thyroid function by enhancing the hypothalamic-pituitary-thyroid (HPT) axis, potentially increasing TSH-stimulated synthesis and release of T4 and T3 from the thyroid gland. It may also enhance peripheral conversion of T4 to T3 by upregulating hepatic 5'-deiodinase activity.
Timing Advice
If approved by your doctor, take thyroid medication first thing in the morning on an empty stomach as prescribed. Ashwagandha can be taken later in the day with food. Separate by at least 2-4 hours to minimize absorption interference.
Our Recommendation
Do not start ashwagandha while on thyroid medication without consulting your endocrinologist. If combining under medical supervision, monitor thyroid function (TSH, free T3, free T4) every 6-8 weeks initially. Be alert for symptoms of hyperthyroidism. Those with Graves' disease or hyperthyroidism should avoid ashwagandha entirely.