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Phenergan: 7 things you should know

Medically reviewed by Carmen Fookes, BPharm. Last updated on July 14, 2022.

1. How it works

  • Phenergan is a brand (trade) name for promethazine which may be used to treat various conditions such as allergies, rhinitis, nausea or vomiting, or insomnia.
  • Promethazine (Phenergan) works on histamine-1 (H1) receptors. H1-receptors are present in the bronchial tubes and in the circulatory system. The attachment of histamine to these receptors causes bronchoconstriction and increased vascular permeability, which leads to plasma leakage. H1-receptors are also present on T cells, B cells, monocytes, and lymphocytes, and stimulation of these receptors induces pro-inflammatory effects. Phenergan can also be used to treat nausea and motion sickness and may have weak effects on other receptors such as dopamine, although this is estimated to be 1/10th that of chlorpromazine.
  • Promethazine (Phenergan) belongs to the class of medicines known as phenothiazines.

2. Upsides

  • May be used in the treatment of rhinitis (vasomotor and allergic), conjunctivitis due to allergies or foods, mild urticaria (itchy rash), and other allergic reactions. May also be used together with epinephrine for more severe allergic reactions (such as anaphylaxis) after the acute event has been controlled.
  • May be used for the prevention or treatment of motion sickness.
  • May be used as a sedative pre- or post-operatively or in women during labor. Relieves apprehension and produces a light sleep from which a person can be easily aroused.
  • May be used in the prevention and control of nausea associated with surgery or anesthesia.
  • Available as an oral tablet, an oral syrup, a compounding powder, in an injectable form, and as a suppository (for rectal use).
  • Available as 12.5mg, 25mg, and 50mg tablets and rectal suppositories.
  • Phenergan is available as a generic under the name promethazine.

3. Downsides

If you are between the ages of 18 and 60, take no other medication or have no other medical conditions, side effects you are more likely to experience include:

  • Drowsiness, which may affect a person's ability to drive or operate machinery. Avoid alcohol and performing hazardous tasks.
  • Heart rate disturbances, dry mouth, confusion, tinnitus (a ringing in the ears), double vision, anxiety, and dizziness have also been reported.
  • Rarely, respiratory depression (unusually slow and shallow breathing); children are more at risk. Avoid in children aged less than 2 years because fatalities have been reported.
  • Rarely may cause unusual symptoms such as oculogyric crisis (prolonged upward deviation of the eyes) torticollis (head involuntarily turned to one side) and tongue protrusion. Confusion, tinnitus (ringing in the ears), hyperexcitability, and seizures have also been reported.
  • Occasionally, paradoxical reactions (the opposite of what is to be expected) may occur. Symptoms include excitability and nightmares. Children and elderly people may be more prone to these effects.
  • May not be suitable for some people including those with pre-existing breathing difficulties (such as asthma, COPD, sleep apnea), a history of seizures, a sulfite allergy, glaucoma, genitourinary problems, who are immunocompromised, bone marrow depression, or with heart or liver disease. Avoid in people who are comatose.
  • May interact with a number of other drugs including antidepressants, antipsychotics, and other drugs that cause sedation.
  • Rarely has been associated with a potentially fatal symptom complex known as Neuroleptic Malignant Syndrome (NMS), sometimes in combination with antipsychotics. Symptoms include fever, muscle rigidity, altered mental status, irregular or fast pulse, or cardiac dysrhythmias.
  • Phenergan should only be used during pregnancy if the potential benefits outweigh the risks to the fetus. Use of Phenergan within two weeks of delivery may inhibit platelet aggregation in the newborn. It is not known if Phenergan is excreted into human milk.

Note: In general, seniors or children, people with certain medical conditions (such as liver or kidney problems, heart disease, diabetes, seizures) or people who take other medications are more at risk of developing a wider range of side effects. View complete list of side effects

4. Bottom Line

  • Phenergan may be used to relieve allergy symptoms, nausea, or as a sleeping aid. Sedation is the main side effect.

5. Tips

  • Phenergan is available as tablets or suppositories. Use the lowest dose possible to relieve your symptoms. Do not take more than the recommended amount.
  • Administer tablets without regard to meals. But if stomach upset occurs; administer with meals.
  • Phenergan may cause drowsiness and affect your ability to drive or operate machinery. Do not perform hazardous tasks if Phenergan affects you in this way.
  • Suppositories are administered into the rectum. Wash your hands and then remove the Phenergan suppository from the foil packaging. Moisten the suppository with cold water. Lie down on your side with one knee pulled up to the chest and use your finger to push the suppository into the rectum.
  • When taking Phenergan to aid sleep, administer just before bedtime. When used to prevent motion sickness, administer 30 minutes to one hour before travel.
  • Do not use in children under the age of 2 years as a number of cases of respiratory depression (marked slow-down in breathing) have been reported, some fatal.
  • Caution when giving to children older than 2 years. Only give after medical advice at the lowest effective dose.
  • Alcohol is best avoided while taking Phenergan because it may increase the risk of sedation and respiratory depression.
  • Avoid excessive sun exposure or artificial ultraviolet light while receiving Phenergan; seek medical advice if skin redness or skin eruptions develop. Wear sun-protective clothing and consider an SPF30+ sun protection when outside if exposure to sunlight is unavoidable.
  • Report any unusual facial or body movements to a doctor. Also seek urgent medical advice if you develop confusion, hallucinations, an irregular heartbeat, a yellowing of the skin or eyes, or any other side effects of concern.
  • Do not use Phenergan during pregnancy or breastfeeding unless your doctor has told you it is safe to do so.

6. Response and effectiveness

  • Phenergan's effects are noticeable within 20 minutes of oral administration. Its effects last for 4-6 hours, although they may persist for up to 12 hours in some people.

7. Interactions

Medicines that interact with Phenergan may either decrease its effect, affect how long it works for, increase side effects, or have less of an effect when taken with Phenergan. An interaction between two medications does not always mean that you must stop taking one of the medications; however, sometimes it does. Speak to your doctor about how drug interactions should be managed.

Common medications that may interact with Phenergan include:

  • anticholinergics, such as benztropine
  • antidepressants, such as amitriptyline, clomipramine, desipramine, doxepin, escitalopram, imipramine, or nortriptyline
  • antifungals, such as voriconazole
  • antipsychotics, such as haloperidol, thioridazine, or ziprasidone
  • barbiturates, such as phenobarbital
  • benzodiazepines, such as diazepam, oxazepam, and temazepam
  • bupropion
  • diabetes medications, such as glimepiride, glyburide, glipizide, or insulin
  • diuretics, such as furosemide
  • droperidol
  • famotidine
  • heart medications, such as amiodarone, felodipine, sotalol, quinidine, or procainamide
  • HIV medications, such as efavirenz or saquinavir
  • medications used to treat ADHD such as dextroamphetamine or lisdexamfetamine
  • metoclopramide
  • mifepristone
  • monoamine oxidase inhibitors, such as isocarboxazid, selegiline, or tranylcypromine
  • moxifloxacin
  • nilotinib
  • opioids, such as oxycodone, methadone, morphine, or codeine
  • Parkinson's disease medications, such as selegiline
  • pimozide
  • potassium chloride or potassium citrate
  • sedatives, or any medication that causes sedation, such as sleeping pills, muscle relaxants, or other antidepressants
  • St John's wort
  • tamoxifen
  • topiramate
  • tramadol
  • other medications that contain promethazine
  • other medications used to treat allergies.

Alcohol may enhance the sedative effects of Phenergan.

May cause false-negative or false-positive results in pregnancy tests that are based on immunological reactions between HCG and anti-HCG.

Note that this list is not all-inclusive and includes only common medications that may interact with Phenergan. You should refer to the prescribing information for Phenergan for a complete list of interactions.


Further information

Remember, keep this and all other medicines out of the reach of children, never share your medicines with others, and use Phenergan only for the indication prescribed.

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.

Copyright 1996-2023 Revision date: July 14, 2022.