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Promethazine: 7 things you should know

Medically reviewed by Carmen Fookes, BPharm. Last updated on July 13, 2022.

1. How it works

  • Promethazine may be used to treat various conditions such as allergies, rhinitis, nausea or vomiting, or insomnia.
  • Promethazine 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. Promethazine 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 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 12.5mg, 25mg, and 50mg tablets and rectal suppositories.
  • Generic promethazine is available.

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. Other hazardous tasks or tasks that require mental alertness may also be affected. Avoid alcohol.
  • Heart rate disturbances, dry mouth, confusion.
  • Rarely, respiratory depression (unusually slow and shallow breathing); children are more at risk. Avoid in children aged less than 2 years.
  • FD&C Yellow No. 5 (tartrazine) is contained in some products. This may cause allergic-type reactions (including bronchial asthma) in certain susceptible persons; people with an aspirin hypersensitivity may be more at risk.
  • 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. Should be used with caution in people with bone-marrow depression.
  • 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, and genitourinary problems, who are immunocompromised, bone marrow depression, or have heart or liver disease. Avoid in people who are comatose.
  • Has also been associated with Neuroleptic Malignant Syndrome (a potentially fatal condition associated with fever, rigidity, altered mental status, blood pressure, and heart rate changes).
  • May interact with several 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.
  • Promethazine should only be used during pregnancy if the potential benefits outweigh the risks to the fetus. Use of promethazine within two weeks of delivery may inhibit platelet aggregation in the newborn. It is not known if promethazine 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

  • Promethazine may be used to relieve allergy symptoms and nausea. Sedation is the main side effect.

5. Tips

  • Administer without regard to meals. But if stomach upset occurs; administer with meals.
  • When used as a sedative, administer just before bedtime. When used to prevent motion sickness, administer 30 minutes to one hour before travel.
  • Available in tablet, solution, syrup, or suppository form. Use the lowest dose possible to relieve your symptoms. Do not take more than the recommended amount.
  • Do not use in children under the age of 2 years as several cases of respiratory depression (marked slow-down in breathing) have been reported, some fatal.
  • Caution when giving to children over 2 years. Use the lowest possible dose under medical advice.
  • Avoid prolonged exposure to the sun.
  • Report any unusual muscle movements to a doctor.
  • May cause drowsiness and affect your ability to drive or operate machinery. Do not perform hazardous tasks if promethazine affects you in this way.
  • Suppositories are administered into the rectum. Wash your hands and then remove the promethazine 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.
  • Alcohol is best avoided while taking promethazine because it may increase the risk of sedation and respiratory depression.
  • Avoid excessive sun exposure or artificial ultraviolet light while receiving promethazine; seek medical advice if skin redness or skin eruptions develop. Wear sun-protective clothing and consider 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 promethazine during pregnancy or breastfeeding unless your doctor has told you it is safe to do so.

6. Response and effectiveness

  • Promethazine'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 promethazine may either decrease its effect, affect how long it works, increase side effects, or have less of an effect when taken with promethazine. 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 promethazine include:

  • 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 promethazine.

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 promethazine. You should refer to the prescribing information for promethazine for a complete list of interactions.


  • Promethazine. Revised 06/2022.

Further information

Remember, keep this and all other medicines out of the reach of children, never share your medicines with others, and use promethazine 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 13, 2022.