The mechanism(s) by which nicotine might be acting are not well established, but studies have suggested that nicotine alters brain circuitry by affecting leptin signalling in the hypothalamus; a role is also implicated for central hypothyroidism induced by a hypothalamic–pituitary dysfunction (Behl et al. 2013; see “Maternal Smoking During Pregnancy/Nicotine Literature Review Documents,” Thayer et al. 2012). This evidence concerns the gene LEP and Central hypothyroidism.