After controlling for covariates, women taking opioids had higher odds of Class II (OR = 1.6, 95% CI = 1.1–2.3) or III obesity (OR = 1.6, 95% CI = 1.1–2.5), and lower levels of serum folate, iron, and transferrin saturation. This evidence concerns the gene TF and obesity due to melanocortin 4 receptor deficiency.