CYP2C19 and obesity due to melanocortin 4 receptor deficiency: Due to a possible decrease in efficacy in these patients, the FDA has issued a boxed warning for CYP2C19 poor metabolizers; however, multivariate analysis results indicate that other factors, such as age, sex, obesity, concurrent diseases and drug–drug interactions, may also play a role in the overall between-subject variability in treatment response.