Shawty Lo's Cause of Death

Shawty Lo died of blunt force trauma -- but he had painkillers on him when he died, and smelled of alcohol ... TMZ has learned.

The rapper's autopsy report reveals Shawty suffered the blunt force injuries to the head when he was ejected from his vehicle in a car crash last month. The Fulton County Medical Examiner also found a prescription bottle on him labeled "Promethazine" ... which was actually filled with Percocet and Vicodin.

The medical examiner goes on to say Shawty's body bag emitted a strong smell of alcohol when opened ... but the official toxicology results are not in yet.

Here's another doozy ... the medical examiner says 2 females were in the car with Shawty at the time of the crash, and asked cops on scene if they could take a bunch of cash out of his pockets. The cops allegedly let 'em do it ... leaving behind around $16.