Promethazine is in a group of drugs called phenothiazines (FEEN-oh-THYE-a-zeens). It works by changing the actions of chemicals in your brain. Promethazine also acts as an antihistamine. It blocks the effects of the naturally occurring chemical histamine in your body.
Promethazine is used to treat allergy symptoms such as itching, runny nose, sneezing, itchy or watery eyes, hives, and itchy skin rashes.
Promethazine also prevents motion sickness, and treats nausea and vomiting or pain after surgery. It is also used as a sedative or sleep aid.
Promethazine is not for use in treating symptoms of asthma, pneumonia, or other lower respiratory tract infections.
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severe drowsiness, weak or shallow breathing;
a light-headed feeling, like you might pass out;
confusion, agitation, hallucinations, nightmares;
fast or slow heartbeats;
jaundice (yellowing of the skin or eyes);
uncontrolled muscle movements in your face (chewing, lip smacking, frowning, tongue movement, blinking or eye movement);
easy bruising or bleeding (nosebleeds, bleeding gums);
sudden weakness or ill feeling, fever, chills, sore throat, mouth sores, red or swollen gums, trouble swallowing; or
severe nervous system reaction--very stiff (rigid) muscles, high fever, sweating, confusion, fast or uneven heartbeats, tremors, feeling like you might pass out.
Side effects such as confusion and severe drowsiness may be more likely in older adults.
Common side effects may include:
ringing in your ears;
dry mouth; or
tired feeling, sleep problems (insomnia).
The average dose is 25 mg taken before retiring; however, 12.5 mg may be taken before meals and on retiring, if necessary. Single 25-mg doses at bedtime or 6.25 to 12.5 mg taken three times daily will usually suffice. After initiation of treatment in children or adults, dosage should be adjusted to the smallest amount adequate to relieve symptoms. The administration of promethazine hydrochloride in 25-mg doses will control minor transfusion reactions of an allergic nature.