A new study finds the percentage of drivers involved in fatal car crashes who tested positive for prescription opioids rose seven-fold between 1995 and 2015.

Researchers from Columbia University analyzed data from nearly 37,000 drivers who died within one hour of a motor vehicle crash. They found 24 percent had drugs in their system, of which 3 percent were prescription opioids, HealthDay reports. Among drivers who tested positive for prescription opioids, 30 percent also had high blood alcohol levels, and 67 percent had traces of other drugs.

The findings appear in the American Journal of Public Health.

“Prescription opioids as potent pain medications can cause drowsiness and impair cognitive functions. The 700 percent rise in the prevalence of prescription opioids detected in fatally injured drivers is cause for great concern,” lead researcher Guohua Li, MD, DrPH, said in a statement.