Trimethobenzamide (Intramuscular)

Classified as an antiemetic, Trimethobenzamide may work by decreasing activity in the area of the brain that causes nausea and vomiting.


Trimethobenzamide is normally prescribed to treat nausea and vomiting after surgery. Treating these symptoms can prevent dehydration. It may be taken orally or intramuscularly, and should not be used by children unless recommended by a doctor, as side effects may be more serious in children. Pediatric patients should also consult their doctor before taking Trimethobenzamide.

Symptoms associated with gastroenteritis (stomach flu) may also be alleviated using Trimethobenzamide.

Conditions treated

  • Nausea and Vomiting

Type of Medicine

  • Antiemetic

Side Effects

The most common side effects experienced by patients taking Trimethobenzamide have been drowsiness and dizziness. Blurred vision, muscle cramps, headaches, diarrhea, unusual tiredness, and depression have also been reported. Many people taking this medication do not experience serious side effects.

Some side effects may occur that do not need immediate medical attention, as they may lessen as the body adjusts to the medication. If the aforementioned side effects are severe, or they continue or worsen, the patient should consult his or her doctor immediately.

In rare cases, patients have experienced mouth sores, confusion, slow speech, yellowing of the skin or eyes, coma, dark urine, and seizures. If the patient experiences any of these symptoms, they should consult a healthcare professional immediately.

Serious allergic reactions to Trimethobenzamide are rare. Side effects associated with an allergic reaction may include rash, itching/swelling, severe dizziness, and trouble breathing. If the patient notices any of these or similar side effects, they should consult their doctor or pharmacist.


Trimethobenzamide should only be used to treat nausea and vomiting. Do not use more than directed by a doctor, as doing so may increase the chance of side effects. This medication may be administered either orally via capsule or intramuscularly as a shot.

The patient may receive Trimethobenzamide intramuscularly via a shot given by a trained health professional. This method may be used a few times until the patient's condition improves, and, if necessary, the patient may switch to oral medicine as prescribed by a doctor. The rest of this description refers to taking the medication orally, as a shot of this medication will always be given by a medical professional.

Dose size and frequency depend on the particular needs of the patient and doctor's recommendation. Factors considered are medical condition, age, and response to therapy. Although there are standard dose sizes and frequencies with this medication, it is important that the patient follows the instructions of their doctor and take exactly as much as directed.

The average dose for a Trimethobenzamide capsule is 300 milligrams (mg) to be taken three or four times a day, as needed. Patients should not use more than directed by their doctor.

Capsules should be taken at about the same time every day. Patients should follow instructions on the prescription label carefully.

If a patient misses a dose, he or she should take it as soon as possible. However, if it is almost time for the next dose, the patient should not double dose. Taking a double dose will increase the chance of side effects.

There is no standard dose size for children, as they have a higher probability of experiencing side effects from this medication. A doctor will determine if this medication is appropriate based on the particular case and prescribe a dose accordingly. It is important that children do not use more than the prescribed dosage.

If overdose is suspected, the patient should contact a poison control center or emergency room immediately. In the United States, an emergency room can be reached by calling 911. A local poison control center can be located by calling 1-800-222-1222.

If symptoms do not improve or worsen from use of Trimethobenzamide, the patient should consult their doctor.

Major Drug Interactions

The patient's doctor may be aware of any possible drug interactions and may already be monitoring them. However, it is important that the patient discloses to their doctor all medications in use so that the doctor can make an informed decision about prescribing medication. The use of alcohol, tobacco, recreational drugs, as well as herbal products may be relevant when considering use of this medication.

Especially relevant to Trimethobenzamide is the use of over the counter drugs, drowsiness being one of the most common side effects. The use of other medications may augment this symptom.

The patient should notify their doctor if they are taking any of the following:

  • antihistamines (e.g. diphenhydramine)
  • anti-seizure drugs (e.g. carbamazepine)
  • medicine for sleep or anxiety (e.g. alprazolam, diazepam, zolpidem)
  • muscle relaxants
  • narcotic pain relievers (e.g. codeine)
  • psychiatric medicines (e.g. chlorpromazine, risperidone, amitriptyline, trazodone)
  • barbiturates

The above list is not exhaustive, and patients are encouraged to disclose to their doctor all the medications (including over the counter) and supplements they are taking. Drugs that are meant to treat anxiety and depression, including sedatives, hypnotics, opiates, anxiolytics, antipsychotics, and anticholinergics may interact with Trimethobenzamide. If the patient is taking or has taken any of these types of medications, it is important to notify their doctor. The doctor will then be able to determine the regimen of the patient based on their individual needs.

The use of alcohol and Trimethobenzamide together will increase drowsiness and the related effects of both substances. It is not recommended that they are taken concurrently.


The patient should tell their doctor of any allergies that they have before taking Trimethobenzamide. This medication may contain inactive ingredients which may induce a reaction in the patient. Thus, the patient should tell their doctor of all allergies, including past medications, foods, dyes, preservatives, and animals. The patient should read all labels carefully to prevent an allergic reaction.

Conditions that affect the brain and/or liver like Reye's Syndrome, encephalitis, and liver disease should be brought to the attention of the doctor. The patient should also alert their doctor of kidney and intestinal problems, or the past occurrence of high fever, dehydration, or electrolyte imbalance.

If the patient experiences drowsiness or blurred vision as a result of using the medication, they should refrain from driving or operating machinery. The use of alcohol in concurrence with Trimethobenzamide may exacerbate these effects.

Use of Trimethobenzamide in children and the elderly has not been sufficiently studied for a standard recommendation of its use. Due to the toxicity of this medication, children may not respond well, especially if they have chickenpox or the flu. The elderly may have problems processing this medication due to declining liver function. The patient (or their guardian) and the doctor should determine the potential pros and cons of using Trimethobenzamide based on their individual needs.

There are no definitive studies on the effects of the medication during pregnancy and breastfeeding. Preliminary studies seem to point to no adverse effects.

As of April 2007, suppositories containing Trimethobenzamide have no longer been marketed in the United States, by order of the Food and Drug Administration (FDA). They have not been shown to treat nausea and vomiting.


Trimethobenzamide should be stored in a tightly closed container (ideally in the one that it came in) at room temperature. It should be kept away from heat, moisture, and direct light. If the patient's bathroom is not properly ventilated or temperature controlled, it may not be a good environment for storage. The medication should also be kept from freezing.

It is important to keep Trimethobenzamide out of reach of children.

Medication that is no longer needed or has expired should not be flushed down the toilet. The patient should talk to their doctor or visit the Food and Drug Administration's website for more information about how to dispose of medicine.


Trimethobenzamide is a drug that is often prescribed after surgery to alleviate nausea and vomiting, though it may in some cases be recommended by a doctor for symptoms related to gastroenteritis, or stomach flu. Designed to decrease activity in the part of the brain that causes nausea and vomiting, Trimethobenzamide can be administered by a healthcare professional as a shot, or taken as a tablet at home.

Side effects are rarely serious and are most commonly drowsiness and/or dizziness. More serious side effects could occur, and the patient is encouraged to consult their healthcare professional immediately if they experience any difficulties. Trimethobenzamide may interact with other medications and therefore it is essential that the patient is upfront with their doctor about their past medical history, their current health regimen, and their lifestyle. Typical symptoms like drowsiness may be made worse by the consumption of alcohol or tobacco and the patient should take care to not drive or operate machinery when feeling impaired.

When taken correctly, Trimethobenzamide relieves discomfort during post-op recovery or helps with symptoms of the stomach flu. Preventing nausea and vomiting can be instrumental in avoiding further health complications related to dehydration. The patient and doctor should work closely together to determine proper dosage and maintain communication about the status of symptoms to ensure that the medication is effectively and safely administered.

Last Reviewed:
December 24, 2017
Last Updated:
April 03, 2018
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