Cadillac Police Officers pulled a vehicle over early Saturday morning on S. Mitchel St. for driving without headlights on.
Police say there were two men in the car and the driver admitted to drinking and driving.
When asked to step out of the vehicle for a breath test, the driver sped away, leading officers on a short chase.
It ended on Laurel St. when the vehicle drove off the road and crashed into a retaining wall, a parked vehicle and a tree.
Police say both men ran from the crashed vehicle.
The passenger has not been found.
The driver was arrested and taken to Munson Hospital Cadillac for medical treatment.
Officers say it appears the driver may have ingested a lethal dose of illegal narcotics during arrest.
He died at the hospital.
Illegal drugs, a handgun and a large amount of cash were also found.
The Michigan State Police is now investigating the death and a medical examiner is conducting an autopsy.
This case is an active ongoing investigation.