The U.S. Surgeon General on Thursday urged individuals and families at risk of opioid abuse to keep a medication on hand that reverses the effects of an overdose.

The medication, naloxone, has become increasingly available at pharmacies without a prescription and is widely carried by police and emergency personnel. The advisory from Surgeon General Jerome Adams—the first surgeon general’s public health advisory in 13 years—reflects growing concern about the scope of an epidemic that saw a 21% increase in opioid overdose deaths...