Death rates from drug overdoses started to rise years before the current opioid crisis began, a new study suggests.

Drug overdose deaths have been increasing for almost 40 years, involving drugs including methamphetamine and cocaine, The Wall Street Journal reports. The type of drug and the demographics of those who die from overdoses have shifted over the years, the researchers report in Science. As the use of one drug declines, another drug attracts new groups of people from different geographic regions, they found. The researchers conclude prevention efforts must extend beyond control of specific drugs to address deeper factors driving the epidemic.

“The current epidemic of overdose deaths due to prescription opioids, heroin and fentanyl appears to be the most recent manifestation of a more fundamental, longer-term process,” senior author Donald S. Burke, M.D., of the University of Pittsburgh said in a news release. “Understanding the forces holding these multiple individual drug epidemics together in a tight upward exponential trajectory will be important in revealing the root causes of the epidemic, and this understanding could be crucial to prevention and intervention strategies.”