Promethazine is an antihistamine. It blocks the effects of the naturally occurring chemical histamine in your body.

Take Promethazine exactly as prescribed by your doctor. Do not take it in larger amounts or for longer than recommended. Follow the directions on your prescription label.
This medication can cause you to have unusual results with certain medical tests. Tell any doctor who treats you that you are using Promethazine.

Get emergency medical help if you have any of these signs of an allergic reaction: hives; difficulty breathing; swelling of your face, lips, tongue, or throat.
Stop using Promethazine and call your doctor at once if you have any of these serious side effects:
twitching, or uncontrollable movements of your eyes, lips, tongue, face, arms, or legs; tremor (uncontrolled shaking), drooling, trouble swallowing, problems with balance or walking; feeling restless, jittery, or agitated; high fever, stiff muscles, confusion, sweating, fast or uneven heartbeats, rapid breathing; feeling like you might pass out; seizure (convulsions); pale skin, easy bruising or bleeding, fever, sore throat, flu symptoms; decreased night vision, tunnel vision, watery eyes, increased sensitivity to light; hallucinations, agitation; nausea and stomach pain, skin rash, and jaundice (yellowing of the skin or eyes); urinating less than usual or not at all; joint pain or swelling with fever, swollen glands, muscle aches, chest pain, vomiting, unusual thoughts or behavior, and patchy skin color; or
slow heart rate, weak pulse, fainting, slow breathing (breathing may stop).
Less serious Promethazine side effects may include:
dizziness, drowsiness, anxiety; blurred vision, dry mouth, stuffy nose; ringing in your ears; weight gain, swelling in your hands or feet; impotence, trouble having an orgasm; or constipation.

Tell your doctor if you are using any of the following medicines:
lithium (Eskalith, Lithobid);
atropine (Atreza, Sal-Tropine), belladonna (Donnatal, and others), benztropine (Cogentin), dimenhydrinate (Dramamine), methscopolamine (Pamine), or scopolamine (Transderm-Scop);
blood pressure medication such as guanadrel (Hylorel), guanethidine (Ismelin), propranolol (Inderal), and others;
a blood thinner such as warfarin (Coumadin);
bronchodilators such as ipratropium (Atrovent) or tiotropium (Spiriva);
bladder or urinary medications such as oxybutynin (Ditropan, Oxytrol), solifenacin (Vesicare), and others;
an MAO inhibitor such as isocarboxazid (Marplan), tranylcypromine (Parnate), phenelzine (Nardil), or selegiline (Eldepryl, Emsam); or
medicines to treat Parkinson's disease, restless leg syndrome, or pituitary gland tumor (prolactinoma); or
medicine to treat stomach ulcer or irritable bowel syndrome, such as dicyclomine (Bentyl), glycopyrrolate (Robinul), hyoscyamine (Anaspaz, Cystospaz, Levsin, and others), mepenzolate (Cantil), or propantheline (Pro-Banthine).
Tell your doctor about all your prescription and over-the-counter medications, vitamins, minerals, herbal products, and drugs prescribed by other doctors.

Seek emergency medical attention if you think you have used too much of this medicine. Overdose symptoms may include severe drowsiness, dizziness, dry mouth, large pupils, flushing, nausea, vomiting, shallow breathing, and fainting.

Stop using Promethazine and call your doctor at once if you have twitching or uncontrollable movements of your eyes, lips, tongue, face, arms, or legs. These could be early signs of dangerous side effects. Promethazine should not be given to a child younger than 2 years old. Phenergan can cause severe breathing problems or death in a child younger than 2.

Take the missed dose as soon as you remember. If it is almost time for your next dose, skip the missed dose and take the medicine at the next regularly scheduled time. Do not take extra medicine to make up the missed dose.

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.

Store this medication at room temperature away from moisture, heat, and light.

Do not use Promethazine if you have severe asthma, emphysema, or other breathing problem, or if you are allergic to Promethazine or other phenothiazines such as chlorpromazine (Thorazine), fluphenazine (Permitil), perphenazine (Trilafon), prochlorperazine (Compazine, Compro), thioridazine (Mellaril), or trifluoperazine (Stelazine).