Substance use disorders involving illicit and prescription drugs are a serious public health issue. In the United States, millions of individuals need treatment for substance use disorders but few receive it. The rising number of drug overdose deaths and the changing legal status of marijuana pose new challenges. In this position paper, the American College of Physicians maintains that substance use disorder is a treatable chronic medical condition and offers recommendations on expanding treatment options, the legal status of marijuana, addressing the opioid epidemic, insurance coverage of substance use disorders treatment, education and workforce, and public health interventions.