Mounjaro side effects: what the Canadian product monograph says

Most common side effects

The product monograph says that the most frequently reported adverse reactions in clinical trials were gastrointestinal disorders, including nausea, diarrhea and vomiting. In general, these reactions were mild or moderate in severity.

The majority of reports of nausea, vomiting and/or diarrhea occurred during dose escalation and decreased over time.

The patient information also lists belching, bloating of the stomach, change in taste, feeling tired, gas and increased heart rate. It lists injection site reactions, reflux or heart burn, unusual skin sensations and weight loss.

In patients aged 10 to less than 18 years, the monograph reports a higher incidence of vomiting, abdominal pain and hypoglycemia than in adults.

The numbers below are from 2 placebo-controlled trials in adults with type 2 diabetes. Each line gives the share of patients on Mounjaro 5 mg, 10 mg and 15 mg, then on placebo.

• Nausea: 12.2%, 15.4% and 18.3%. Placebo: 4.3%.
• Diarrhea: 11.8%, 13.3% and 16.6%. Placebo: 8.9%.
• Decreased appetite: 5.5%, 9.6% and 11.2%. Placebo: 1.3%.
• Vomiting: 5.1%, 5.0% and 9.1%. Placebo: 2.1%.
• Dyspepsia: 8.0%, 7.5% and 5.4%. Placebo: 2.6%.
• Constipation: 5.9%, 5.8% and 6.6%. Placebo: 1.3%.
• Abdominal pain: 5.9%, 4.6% and 5.4%. Placebo: 4.3%.

Serious warnings and precautions box

The box in the product monograph is about the risk of thyroid C-cell tumors. Tirzepatide, the medicinal ingredient in Mounjaro, increased the risk of thyroid C-cell tumors in rats. It is not known if the risk seen in rats applies to humans.

The box says that it is uncertain if Mounjaro may increase your risk of thyroid C-cell tumors, including medullary thyroid carcinoma.

The box says: do not use Mounjaro if you have a personal or family history of medullary thyroid cancer (MTC). It says the same for Multiple Endocrine Neoplasia syndrome type 2 (MEN 2).

The monograph gives these examples of symptoms of thyroid tumors: a mass in the neck, dysphagia, dyspnea and persistent hoarseness.

Who must not use Mounjaro

The monograph says that Mounjaro should not be used in patients with type 1 diabetes, or for the treatment of diabetic ketoacidosis.

Mounjaro is not indicated for use in patients less than 10 years of age.

If a patient wishes to become pregnant, the monograph says that Mounjaro should be discontinued at least 1 month before a planned pregnancy.

The patient information says not to use Mounjaro in these cases:

• You are allergic to tirzepatide, to any ingredient in Mounjaro or to a component of its container. This includes benzyl alcohol, the preservative in Mounjaro KwikPen.
• You or a member of your family has ever had medullary thyroid cancer (MTC).
• You have Multiple Endocrine Neoplasia syndrome type 2 (MEN 2).
• You are pregnant. The patient information says that Mounjaro may harm your unborn baby.

Other warnings in the monograph

The monograph also describes these risks:

• Pancreatitis: if pancreatitis is suspected, Mounjaro should be discontinued. If pancreatitis is confirmed, Mounjaro should not be restarted.
• Low blood sugar: patients who take Mounjaro with a sulfonylurea or insulin may have an increased risk of hypoglycemia.
• Gallbladder disease: in placebo-controlled trials, 0.6% of patients on Mounjaro and 0% of patients on placebo reported acute gallbladder disease.
• Kidney problems: nausea, vomiting and diarrhea can cause dehydration. Dehydration can lead to kidney problems, such as sudden kidney failure.
• Eye disease: fast improvements in blood sugar control may lead to a temporary worsening of diabetic eye disease.
• Malnutrition: malnutrition has been reported in patients who receive Mounjaro, including severe, serious and fatal events.
• Heart rate: Mounjaro causes an increase in heart rate.
• Oral birth control: the monograph advises patients who use it to switch to a non-oral method, or to add a barrier method. The barrier method is for 4 weeks after the start and for 4 weeks after each dose increase.
• Anesthesia: the patient information says to tell your healthcare professional that you take Mounjaro before a procedure with general anesthesia or deep sedation.
• Benzyl alcohol: Mounjaro KwikPen contains 5.4 mg benzyl alcohol in each 0.6 mL dose. Benzyl alcohol may cause allergic reactions.
• Other incretin medicines: the use with other GLP-1 receptor agonists or with DPP-4 inhibitors has not been studied. Mounjaro should not be used with them.

When to stop and get medical help

The patient information says to stop Mounjaro and get medical help right away if you have any symptoms of a serious allergic reaction. This can include itching, rash or difficulty breathing.

It says to urgently contact your healthcare professional if you have a sudden loss of vision or rapidly worsening eyesight. It says to speak to your healthcare professional immediately if you have severe and on-going pain in the stomach area. It says to call your healthcare professional right away if you have thoughts or behaviours of harming or killing yourself.

For a suspected overdose, it says to contact a healthcare professional, a hospital emergency department or a regional poison control centre immediately. This applies even if there are no signs or symptoms. The monograph also gives the toll-free number of Health Canada: 1-844-764-7669.

The table of serious side effects lists gastrointestinal problems as very common and diabetic retinopathy as common. It lists severe low blood sugar as uncommon. The frequency of malnutrition is unknown. For these four, the table says to talk to your healthcare professional in all cases.

For the side effects below, the table says to stop taking Mounjaro and get immediate medical help:

• Rare: acute pancreatitis (sudden inflammation of the pancreas). Symptom: prolonged severe abdominal pain with or without vomiting.
• Rare: dehydration that can cause sudden kidney failure. Symptoms: dark yellow and strong-smelling pee, feeling extremely thirsty, feeling dizzy or lightheaded.
• Rare: sudden gallbladder problems. Symptoms: severe abdominal pain, yellowing of your skin, or high fever with chills.
• Frequency unknown: anaphylactic reaction or angioedema (serious allergic reaction). Symptoms: breathing problems, swelling of the throat and face, fast heartbeat.
• Frequency unknown: gastroparesis (slow stomach emptying). Symptoms: pain, severe nausea and vomiting, prolonged belching and prolonged bloating.
• Frequency unknown: ileus (slow movement of food through intestines). Symptoms: inability to tolerate an oral diet, abdominal bloating and pain, severe nausea and vomiting.
• Frequency unknown: non-arteritic anterior ischemic optic neuropathy (NAION, an eye condition). Symptoms: sudden decreased vision (blurring or cloudiness) or permanent loss of vision.

Ask a health professional

This page repeats what the Canadian product monograph says. It is not medical advice. Ask your pharmacist or your prescriber what applies to you.