GENERIC NAME: promethazine and codeine
BRAND NAME: (Phenergan with Codeine: This brand no longer is available in the U.S.)
DRUG CLASS AND MECHANISM: Promethazine is in a class of drugs called phenothiazines which also includes chlorpromazine, and trifluoperazine; however, unlike the other drugs in this class, promethazine is not used as an anti-psychotic but rather as an anti-histamine, sedative, antiemetic (anti-nausea), and cough suppressant.
Cells in the body release histamine during several types of allergic reactions. When histamine binds to its receptors on other cells, it stimulates changes within the cells that lead to release of other chemicals that cause sneezing, itching, and increased mucus production. Antihistamines such as promethazine compete with histamine for one of the receptors for histamine (the H1 receptor) on cells; however, when antihistamines bind to the receptors they do not stimulate the cells. Instead, they prevent histamine from binding and stimulating the cells. Promethazine also blocks the action of acetylcholine, a neurotransmitter that nerves use to communicate with one another, on its receptors (anticholinergic effect), and this may explain its benefit in reducing the nausea of motion sickness. It is used as a sedative because it causes drowsiness as a side effect. The cough suppressant effects may be due to is anticholinergic effects.
Codeine is a weak narcotic pain-reliever and cough suppressant similar to morphine and hydrocodone. In fact, a small amount of codeine is converted to morphine in the body. The precise mechanism of action of codeine is not known; however, like morphine, codeine binds to narcotic receptors in the brain (opioid receptors) that are important for transmitting the sensation of pain throughout the body and brain. Codeine increases tolerance to pain and decreases discomfort, but the pain still is apparent to the patient. In addition to reducing pain, codeine also causes sedation (drowsiness) and depresses breathing. The FDA approved promethazine and codeine in January 1952.
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