Before taking this medicine. You should not take Cheratussin AC if you are allergic to codeine or guaifenesin. In some people, codeine breaks down rapidly in the liver and reaches higher than normal levels in the body. Consumer information about the medication oral guaifensin with codeine (Cheratussin AC, Tussi-Organidin NR, Mytussin AC) side effects, drug interactions, recommended dosages, and storage information. Read more about the prescription drug oral guaifensin with codeine. Learn about Cheratussin AC (Generic Robitussin AC), dosing, proper use and what to know before beginning treatment C Phen ® (as a combination product containing Chlorpheniramine, Phenylephrine)see Phenylephrine; C Phen DM ® (as a combination product containing Chlorpheniramine, Dextromethorphan, Phenylephrine)see Phenylephrine Codeine is an opiate used to treat pain, as a cough medicine, and for diarrhea. It is typically used to treat mild to moderate degrees of pain. Greater benefit may occur when combined with paracetamol (acetaminophen) or a nonsteroidal anti-inflammatory drug (NSAID) such as aspirin or ibuprofen. Evidence does not support its use for acute cough. 2 Answers - Posted in: cheratussin ac, codeine - Answer: Codeine is an opiate, and any opiates will show up on a drug screen.