Withanolides are a group of naturally occurring steroidal lactones found primarily in Withania somnifera (ashwagandha), a herb widely used in Ayurvedic medicine. The traditional use of ashwagandha includes support for overall vitality, stress reduction, and improvement of various bodily functions, including those of the thyroid gland. In recent years, several scientific studies have investigated the effects of withanolides and ashwagandha extracts on thyroid function.

Clinical research, though limited in scale, suggests that ashwagandha supplementation may have a beneficial effect on thyroid hormone levels, particularly in cases of subclinical hypothyroidism. For example, a randomized, double-blind, placebo-controlled study published in 2018 demonstrated that ashwagandha root extract (standardized for withanolide content) improved serum thyroid stimulating hormone (TSH), T3, and T4 concentrations in adults with subclinical hypothyroidism. The proposed mechanisms include modulation of the hypothalamic-pituitary-thyroid axis and reduction of oxidative stress, both of which can influence thyroid function.

However, the body of evidence is still emerging, and most studies involve small sample sizes or are preclinical (animal or in vitro). Therefore, while there is a scientific basis for the use of withanolides in supporting thyroid health, the evidence is not yet robust or conclusive, warranting a moderate rating.