TFRC and obesity due to melanocortin 4 receptor deficiency: After adjustment for covariates, younger women taking opioids had higher odds of class III obesity (OR = 2.1, 95% CI: 1.2–3.7), high serum transferrin receptor (OR = 2.3, 95% CI: 1.2–4.30), and low percent transferrin saturation (OR = 2.6, 95% CI: 1.7–4.2) than unexposed younger women.