Opioid use disorder is the most lethal substance use disorder in current US epidemiology. Overdose deaths from opioids exceeded 80,000 in recent years — driven largely by illicitly manufactured fentanyl in the unregulated drug supply. The pathway from prescription opioid use to illicit use is well-trodden; many patients trace their disease to acute pain prescribing that transitioned over years.
The mu-opioid receptor is the target of clinical opioids (morphine, oxycodone, hydrocodone, fentanyl, heroin). Full mu agonists produce analgesia, euphoria, respiratory depression, constipation, pupillary constriction. The euphoria drives reward learning; the respiratory depression drives overdose death; the chronic activation drives the tolerance and dependence that define OUD.
Medication-assisted treatment substantially reduces mortality. This is the most consistent finding across the OUD treatment literature. MAT reduces overdose deaths, all-cause mortality, opioid use, criminal activity, and HIV/hepatitis transmission. Untreated OUD carries substantial mortality; MAT changes the trajectory.
Three FDA-approved medications:
Buprenorphine — partial mu-opioid agonist. Office-based prescribing (no special DEA registration required as of 2023). Sublingual film or tablet, daily dosing. Now available as monthly LAI (Sublocade). Ceiling effect on respiratory depression makes overdose less likely than with full agonists. Workhorse of modern OUD treatment.
Methadone — full mu-opioid agonist with long half-life. Once-daily dosing through specialized opioid treatment programs (OTPs). Highly effective; has the strongest mortality reduction evidence. Requires daily clinic visits initially, transitioning to take-home doses with stability.
Naltrexone — mu-opioid antagonist. Monthly LAI (Vivitrol) or oral. If patient uses opioid while on naltrexone, the opioid simply does not work. Requires opioid-free interval before initiation (7-10 days for short-acting opioids, longer for long-acting) to avoid precipitated withdrawal. Best for motivated patients without recent active use.
Naloxone (Narcan) saves lives. Co-prescribed with chronic opioid therapy, distributed in harm reduction programs, available without prescription in many jurisdictions, increasingly available in workplaces, schools, public transit. Universal availability is among the strongest single interventions in the overdose epidemic.
Fentanyl-era considerations: buprenorphine induction in fentanyl-exposed patients carries precipitated withdrawal risk. Modern approaches include microdosing protocols (starting 0.5-2 mg with gradual escalation while continuing low-dose fentanyl) and longer waiting periods before induction. Continue MAT indefinitely — early discontinuation drives relapse and overdose death.
When you encounter a patient with OUD, the treatment is effective and lifesaving. Many patients have never been offered MAT despite its evidence base. Buprenorphine office-based, methadone OTP, naltrexone for motivated abstinent patients — all reduce mortality substantially.