Silymarin Improves Thyroid Function in Lithium-treated Bipolar Patients: A Randomized, Double-blind, Placebo-controlled Pilot Study

Background: Thyroid dysfunction is one of the most important side effects of lithium carbonate. Silymarin is a flavonolignan extracted from the milk thistle Silybum marianum (L.), which has remarkable antioxidant and therapeutic properties. This clinical trial study aimed to evaluate the effect of silymarin on thyroid function and serum antioxidant status in patients with lithium-treated bipolar disorder. Methods: Bipolar patients with a depression episode and a history of at least six months of lithium use were randomly divided into placebo-control (n=18) and intervention (n=19) groups. In addition to standard medication, patients in the intervention and control groups received silymarin (140 mg) and placebo tablets daily for ten weeks, respectively. Finally, thyroid function and serum antioxidant status were evaluated along with clinical signs at the beginning and the tenth week. Results: Following the administration of silymarin, a significant increase was observed in total antioxidant capacity (p = 0.004) and total thiol molecules (p = 0.005) levels in serum compared to the placebo group. Although silymarin had no significant effect on serum triiodothyronine (T3) and lithium levels, it could significantly improve the secretory status of thyroid-stimulating hormone (TSH; p = 0.002) and Thyroxine (T4; p = 0.02) hormones in comparison to the placebo group. Conclusion: The current study showed that silymarin might be effective for thyroid function in lithium- treated bipolar patients by improving body’s antioxidant status.