Codeine is an opiate used to treat pain, cough and diarrhea. It is commonly combined with paracetamol (acetaminophen), aspirin or ibuprofen. Codeine is also used recreationally and produces a high similar to, but milder than a morphine high. Common side effects include drowsiness and constipation. Serious side effects may include breathing difficulties and addiction.

Codeine is available in tablet / capsule and syrup forms. In many countries, medications containing codeine are sold on an over-the-counter basis without need for prescription. This ease of access has often contributed to misuse.

While not nearly as strong as morphine or heroin, codeine is still an opiate. This means that continued use can manifest physical withdrawals, mental withdrawals, and ultimately, addiction. Heroin addicts may use codeine to ward off the effects of withdrawal when their drug of choice is unavailable or unaffordable.