Promethazine-codeine cough syrup is a medication that contains codeine. Codeine is an opioid that acts as a cough suppressant. It can also produce relaxation and euphoria when consumed at a higher-than-prescribed dose. It also contains promethazine HCl, an antihistamine that additionally acts as a sedative. Although only available by prescription, promethazine-codeine cough syrup is sometimes diverted for abuse.

Dextromethorphan (DXM) is a cough suppressant found in many over-the-counter cold medicines. It may produce dissociative effects or hallucinations when taken in a high dose. 

Source: NIDA

NIDA Fact Sheet