However, considering that the impact of this agent on TSH in hypothyroid patients was moderate, even if metformin reduces plasma prolactin in hypothyroid men with autoimmune thyroiditis and antipsychotics-induced hyperprolactinemia, this effect is probably weak and secondary to the improvement in the hypothalamic–pituitary–thyroid axis activity but not associated with a direct effect on lactotrophic cells and/or the tuberoinfundibular dopaminergic pathway. This evidence concerns the gene PRL and hyperprolactinemia.