Bolstered by a huge increase in cases involving heroin, the rate at which Americans die from drug overdoses has more than doubled since the end of the millennium.

The Centers for Disease Control and Prevention released data Friday showing the nation’s overdose rate at 16.3 per 100,000 people in 2015 — more than 2.5 times the rate it was in 1999.

The numbers show overdose deaths afflict middle-aged adults and white people the most. Heroin leads the charge, accounting for a quarter of the overdose deaths, more than triple the rate at which it killed in 2010.

States across the country have pledged to curb drug abuse through public policy. In Wisconsin, policy makers launched an opioid task force and facilitated lower prices on an anti-overdose drug. The American Society of Addiction Medicine recently praised New Jersey Gov. Chris Christie and the state’s legislature for mandating insurance cover up to six months of addiction treatment.