The 21-year-old Toyota Vios driver, whose vehicle collided with a SUV on the Penang Bridge, tested positive for marijuana.
Seberang Prai Tengah district police chief Assistant Commissioner Nik Ros Azhan Nik Abd Hamid said the blood test report also showed that he was driving under the influence of alcohol at the time of the incident, which saw the SUV plunging into the sea.
The driver of the SUV, identified as student Moey Yun Peng, 20, was headed to Perai when it was involved in the collision with the Toyota Vios early Sunday.
Search operation for Moey and his vehicle is still ongoing.