The rate of drug overdose deaths continues to increase in the United States, according to a new report from the Centers for Disease Control and Prevention (CDC).

The death rate for drug overdoses reached 19.9 cases per 100,000 people last summer, compared with 16.7 per 100,000 the previous summer, HealthDay reports.

The CDC also found an increase in drug overdose deaths for the 12-month period ending in September 2016, compared with the same period a year before—18.5 overdose deaths per 100,000, up from 16.1 deaths per 100,000.

Of the 52,404 overdose deaths in 2015, the CDC found 33,091 involved opioids. Prescription or synthetic opioid pain relievers were involved in more than two-thirds of opioid-related overdose deaths.