Yes. Misuse of promethazine-codeine cough syrup slows down the central nervous system, which can slow or stop the heart and lungs. Mixing it with alcohol greatly increases this risk.
Overdose can be treated with CPR and certain medications depending on the person's symptoms, but the most important step to take is to call 911. The drug naltrexone can be given to stop an opioid overdose if codeine was taken.