As of 2015, it is only possible to purchase codeine from a pharmacy with a prescription from a doctor, according to MedicineNet. Doctors prescribe codeine for mild-to-moderate pain and to suppress coughs, and it can be combined with acetaminophen or aspirin to increase its pain-relieving effectiveness.
Codeine is a narcotic pain reliever. MedicineNet states that it works similarly to morphine and hydrocodone by binding to opioid receptors in the brain that transmit pain signals. A small amount of codeine converts to morphine in the body. Patients taking codeine are still aware of their pain, but the drug decreases discomfort and increases pain tolerance.
Codeine slows breathing and may cause drowsiness, cautions MedicineNet. Other common side effects include lightheadedness, nausea, shortness of breath, constipation, abdominal pain and rash. Codeine impairs physical and mental abilities, and people taking the drug should use caution when driving or operating other machinery. Combining codeine with alcohol or sedatives such as alprazolam may cause brain impairment or confusion, and patients should not combine these drugs.
The Food and Drug Administration is investigating the safety of codeine to treat coughs in children under age 18, as of July 2015, according to MedlinePlus. Codeine may cause slow or difficult breathing, and children who already have breathing problems or those who have recently had tonsils or adenoids removed may be more susceptible to these side effects.