Among men who inject drugs, methadone maintenance therapy (MMT) may contribute to bone loss through its association with reduced circulating free testosterone and estradiol, according to study results published in Journal of the Endocrine Society. In this cross-sectional study, researchers aimed to explore the underlying associations between MMT, BMD, and sex hormones among individuals who inject drugs. Still, this association became nonsignificant after adjustment for estradiol and free testosterone, suggesting a mediating effect of sex hormones. Methadone and heroin use were strongly associated with low free testosterone among men, with obesity further increasing the risk. The study authors concluded, “MMT use may contribute to decreased lumbar spine BMD in a population of men who inject drugs, which appears to be mediated by both testosterone and estradiol.