Ashwagandha Appears to Raise Thyroid Hormone Levels. Medication Users Should Monitor
Clinical studies show ashwagandha increases T3 and T4 concentrations. For those on levothyroxine or other thyroid drugs, that amplification warrants monitoring.
Ashwagandha (Withania somnifera) is one of the most widely studied adaptogenic herbs, with clinical evidence supporting its effects on stress, cortisol, and sleep. Less discussed is its effect on the thyroid — a finding that matters for the large number of people taking thyroid medication.
What the studies found
Multiple clinical trials have found that ashwagandha supplementation increases circulating thyroid hormone concentrations. A study published in the Journal of Alternative and Complementary Medicine found that 600mg of ashwagandha root extract daily for eight weeks produced significant increases in serum T3 (triiodothyronine) and T4 (thyroxine) compared with placebo in patients with subclinical hypothyroidism.
A separate trial in people with bipolar disorder also noted thyroid hormone changes with ashwagandha supplementation, which prompted investigators to raise caution about use in thyroid-sensitive populations.
The mechanism is not fully established. Ashwagandha may increase the conversion of T4 to the more active T3, reduce thyroid hormone degradation, or directly stimulate production. Whatever the pathway, the effect on measurable hormone levels has been confirmed across multiple studies.
Why this matters for people on thyroid medication
The most commonly prescribed thyroid medication is levothyroxine, a synthetic form of T4. Dosing is calibrated to bring a patient’s thyroid hormone levels into the normal range and to manage symptoms of hypothyroidism such as fatigue, weight gain, and cold intolerance.
If ashwagandha simultaneously raises thyroid hormone levels, the combined effect could push T3 and T4 above the normal range. Excess thyroid hormone — hyperthyroidism — causes symptoms including palpitations, weight loss, insomnia, anxiety, and, over time, bone density loss and cardiac arrhythmias.
The risk is not theoretical. For someone whose levothyroxine dose was carefully titrated over months, adding an adaptogen that independently raises thyroid hormone without adjusting the prescription dose or monitoring lab values introduces genuine uncertainty.
Who needs to be careful
People taking levothyroxine or other thyroid hormones (including liothyronine, dessicated thyroid extract, and combination formulations) should discuss ashwagandha with their prescribing endocrinologist or GP before starting. Periodic thyroid function tests during the period of co-use would allow early detection of any drift outside the target range.
People who have had thyroid cancer and are on suppressive thyroid hormone therapy (where maintaining a specific TSH level is clinically important) should be especially cautious.
Reference
- Examine.com. "Ashwagandha: Thyroid Interactions." examine.com
