After adjustment for covariates, women with obesity taking prescription opioids had higher odds of low red blood cell count (OR = 1.8, 95% CI: 1.1–2.8), and two additional significant effects emerged: higher odds of high transferrin receptor (OR = 2.2, 95% CI: 1.3–3.9), as well as lower odds of low HDL (OR = 0.6, 95% CI: 0.5–0.9). Here, TFRC is linked to obesity due to melanocortin 4 receptor deficiency.