Opioid use disorder is highly prevalent and can be fatal. At least 2.1 million Americans 12 years and older had opioid use disorder in 2016, and approximately 47,000 Americans died from opioid overdoses in 2017. Opioid use disorder is a chronic relapsing condition, the treatment of which falls within the scope of practice of family physicians. With appropriate medication-assisted treatment, patients are more likely to enter full recovery. Methadone and buprenorphine are opioid agonists that reduce mortality, opioid use, and HIV and hepatitis C virus transmission while increasing treatment retention. Intramuscular naltrexone is not as well studied and is harder to initiate than opioid agonists because of the need to abstain for approximately one week before the first dose. However, among those who start naltrexone, it can reduce opioid use and craving. Choosing the correct medication for a given patient depends on patient preference, local availability of opioid treatment programs, anticipated effectiveness, and adverse effects. Discontinuation of pharmacotherapy increases the risk of relapse; therefore, patients should be encouraged to continue treatment indefinitely. Many patients with opioid use disorder are treated in primary care, where effective addiction treatment can be provided. Family physicians are ideally positioned to diagnose opioid use disorder, provide evidence-based treatment with buprenorphine or naltrexone, refer patients for methadone as appropriate, and lead the response to the current opioid crisis.