Promethazine hydrochloride Oral / IV / Suppository / IM (Phenergan®)

Author: OncoLink Team
Last Reviewed: April 10, 2024

Pronounce: proe-METH-a-zeen

Classification: phenothiazine derivative; H1 receptor blocking agent; antiemetic

About: Promethazine hydrochloride Oral / IV / Suppository / IM (Phenergan®)

Promethazine hydrochloride is a phenothiazine derivative that works by changing the actions of certain chemicals in your brain. Promethazine is also an antihistamine. It blocks the effects of histamine, a naturally occurring chemical in your body. By affecting these chemicals in the body, promethazine can:

  • Help treat nausea and vomiting associated with surgery or chemotherapy/radiation.
  • Treat or prevent motion sickness.
  • Help treat symptoms of allergic reactions, such as itching or runny nose, sneezing, itchy/watery eyes, hives, and skin rashes.
  • Be used as a sedative or sleep aid.

Because of how promethazine works in your body, tell your care team if you have a history of or current respiratory (lung) diseases or problems, such as asthma, COPD (chronic obstructive pulmonary disease), sleep apnea, myasthenia gravis, Parkinson’s disease or a history of seizures.

How this Medication Comes

This medication comes as tablets, oral syrup, intramuscular (as a shot, IM), and intravenous (given in a vein, IV) formulations.

How to Take Promethazine

Promethazine can be given on as needed or scheduled basis and should be taken as prescribed by your provider. The dose and how often you take promethazine will depend on why you were prescribed it. You should not drink alcohol while taking promethazine. You should not drive a car or operate heavy machinery until you know how promethazine affects you.

This medication can be affected by certain foods and medications, so they should be avoided. Be sure to tell your healthcare provider about all medications and supplements you take including but not limited to: anticholinergic agents including aclidinium, glycopyrrolate, ipratropium, umeclidinium, tiotropium, metoclopramide, potassium supplement pills, and CNS depressants including buprenorphine and opioid pain medications.

It is important to make sure you are taking the correct amount of medication every time. Before every dose, check that what you are taking matches what you have been prescribed.

Storage and Handling

All oral versions (tablets, syrup) of promethazine should be stored in the original, labeled container at room temperature. The syrup version of promethazine should be in a light-protected bottle with the lid tightly closed at all times. Keep containers out of reach of children and pets.

Where do I get this medication?

The oral form of promethazine is available through retail/mail order pharmacy. Your oncology team will work with your prescription drug plan to identify an in-network retail/mail order pharmacy for medication distribution. You can work with your provider’s office if this medication needs a prior authorization. The intravenous or intramuscular form would be provided to you in a healthcare setting as ordered by your medical team.

Insurance Information

The oral form of this medication may be covered under your prescription drug plan. Patient assistance may be available to qualifying individuals without prescription drug coverage. Co-pay cards, which reduce the patient co-pay responsibility for eligible commercially (non-government sponsored) insured patients, may also be available. Your care team can help you find these resources, if they are available. Administration of the intravenous or intramuscular form in either the outpatient or inpatient setting would be covered under your medical benefits.

Possible Side Effects of Promethazine

This medication is given to manage and/or prevent side effects of your cancer treatment. If you are having side effects from this medication you should talk to your team about if this medication is necessary for your treatment or if there are other options to help manage the side effect this medication is treating. These are some of the most common side effects:

Central Nervous System (CNS) Effects

Because of how this medication works and its effects on neurotransmitters in the brain, promethazine may cause drowsiness, fatigue, sedation, ringing in your ears, feeling nervous, double vision, dizziness, and weakness. If these effects make it hard to carry out daily life, talk with your provider. If you or a caretaker notice you are having a hard time staying awake, or have shallow breathing, call 911 right away.

Anticholinergic Effects

Because of how this medication works, promethazine may cause constipation, dry mouth, blurred vision, or urinary retention. These side effects may be worse if you are elderly and/or are on other medications with similar effects. If these effects make it hard to carry out daily life, talk with your provider.

Less common, but important side effects can include:

  • Respiratory Depression: Promethazine should not be given to patients under 2 years of age. Tell your care team before taking promethazine if you have a history of or current respiratory (lung) diseases or problems. Signs of respiratory depression are slow, shallow breaths, which causes a low oxygen level in your blood. Signs of over-sedation are mental confusion, having a hard time moving, muscle weakness, and having a hard time concentrating. If you or a caretaker notice any of these signs, call 911.
  • Severe Tissue Injury: Promethazine, when given IV or IM, can cause severe irritation and damage to the tissue around the site it was given. Signs of tissue injury can be burning, pain, thrombophlebitis (swelling of a vein that causes a clot), tissue necrosis (death of tissue), and gangrene (death of tissue due to a lack of blood supply to the area). If you have pain, redness, blistering or itching in the skin around or near the injection site during or after receiving promethazine, tell your care provider right away.
  • Lower Seizure Threshold: Promethazine may lower seizure threshold. It should be used with caution in persons with seizure disorders or in persons who are using concomitant medications, such as pain medications or local anesthetics, which may also affect seizure threshold.
  • Bone-Marrow Suppression: Chronic use of promethazine may lower white blood cells and platelets in patients on cytotoxic chemotherapy. Your healthcare team will monitor your labs and adjust and hold this medication as necessary.
  • Neuroleptic Malignant Syndrome (NMS): Promethazine has been linked to a very serious side effect called Neuroleptic Malignant Syndrome (NMS). Signs of NMS are a very high fever, tight or rigid muscles, a change in mental status, a change in pulse or blood pressure, sweating, and irregular heart rhythms. Tell your provider right away if you have any of these symptoms.

Reproductive Concerns

You should consult with your healthcare team prior to becoming pregnant, fathering a child, or breastfeeding while receiving this medication because fetal risk cannot be ruled out in these situations. Risk versus benefits should be weighed and discussed with your healthcare team.


September 1, 2023

Coming Soon: Medicare Drug Price Negotiations

by Christina Bach, MSW, LCSW, OSW-C

July 19, 2022

Managing Side Effects with South Asian Foods

by OncoLink Team

April 29, 2022

Tomorrow is National Prescription Drug Take-Back Day!

by Christina Bach, MSW, LCSW, OSW-C