Genetic Polymorphisms on OPRM1 Involved in Multiple Responses of a Methadone Maintenance Population

The opioid receptor, mu 1 (OPRM1) is a gene that encodes for the mu opioid receptor (MOR). The role of the MOR has been well characterized in both physiological and pharmacological animal studies. Its role in heroin-dependent patients under treatment with the synthetic opioid methadone, however, is unclear. Using a Taiwan methadone maintenance treatment cohort, we have discovered that the genetic polymorphisms on the OPRM1 genetic regions were significantly associated with the severity of smoking. We did this by using the plasma nicotine metabolite cotinine concentrations as indicator, self-reports of methadone-induced insomnia, and change-in-libido side effects, as rated by the treatment emergent symptom scale and the plasma concentrations of macrophage-derived chemokine (MDC). Our results suggest that the OPRM1 genetic variants may be indicators for the severity of smoking, the severity of methadone-induced insomnia and change-in-libido side effects, and the plasma levels of MDC-related immune responses.