What is the difference between robitussin with codeine and promethazine with codeine?

Robitussin with codeine contains guaifenesin, which is an ingredient that is used to treat chest congestion by increasing chest secretions and making it easier for the patient to cough up the secretions.

Promethazine is a drug that is used to treat nausea and vomiting.

Codeine is used in both preparations to treat cough