Chemically, nothing. All three drugs are derived from the opium plant; however, they differ by way of form. Heroin, a Schedule I drug of abuse, can be found in many formats, including powder, pill and liquid. Codeine, which is present in some cold medicines, is converted by the body to morphine, which is usually aqueous. All of these variations of the opium plant are highly addictive and should not be administered without the approval of a medical professional.