Police said they are seeking a formal arrest warrant for the 45-year-old doctor, surnamed Kim, who practices in the affluent Gangnam district of southern Seoul.
A spokesman for the Seocho police precinct told AFP the 30-year-old victim, surnamed Lee, had called Kim to complain she was having trouble sleeping.
At the hospital where he works, Kim administered a five-milligram dose of sedative without a prescription to try to ease her insomnia.
He told police he later found Lee dead when he returned to check on her.
After trying to resuscitate her, Kim said he put the body in a wheelchair and covered the face with a surgical mask. He placed the corpse in Lee’s Audi and drove the car to a riverside park where he abandoned it.
Kim surrendered to police a few hours after a passer-by discovered the body in the car. Police said he is currently accused only of dumping the body but investigations are continuing.