Is Mounjaro Safe?

In most cases, the answer is yes, provided that:

• There is a clinical need (i.e. to treat obesity)
• It is prescribed by a healthcare professional
• It is used as directed

Mounjaro should only be used with a prescription, as it may not be safe otherwise and can cause side effects, some of which may be serious.

Most side effects are mild and improve over time but monitoring them and reporting any concerns to your doctor or pharmacist helps ensure safe treatment.

All patients must start on the lowest 2.5mg dose, as the dosing schedule is designed to introduce tirzepatide gradually and minimise side effects.

You can remain on a lower dose for longer if you are tolerating it well, seeing benefits, and continuing to lose weight.

Before approval, Mounjaro underwent rigorous testing in large clinical trials (called SURMOUNT), looking at how well it works for weight loss.

Surmount trials (for weight loss)

Across SURMOUNT 1-4, the Mounjaro obesity trials enrolled over 5,000 participants.

This represents one of the largest clinical programmes ever conducted for a weight-loss medication

Across all trials, Mounjaro demonstrated a favourable and consistent safety profile:

Most common side effects

• Nausea (32%)
• Diarrhoea (23%)
• Vomiting (12%)
• Constipation (6%)

These gastrointestinal side effects were:

• Most likely during dose increases
• Mostly mild to moderate
• Tended to improve over time

Serious adverse events

• Occurred in roughly 5–7% of tirzepatide users
• Similar rates to placebo, indicating no major safety signal

Discontinuation due to side effects

• Ranged from 4–7% depending on dose
• Higher at 10mg and 15mg, but still low overall

No unexpected safety concerns

Across the entire SURMOUNT programme, no new or unexpected safety issues emerged.

Weight loss results

Average weight loss after 72 weeks:

• 5 mg: 15%
• 10 mg: 19.5%
• 15 mg: 20.9%
• Placebo: 3.1%

Key findings:

Across thousands of patients, the SURMOUNT trials show that Tirzepatide demonstrated:

• Unmatched weight-loss results, with many losing 15–22% of their body weight
• A predictable, largely mild side-effect profile, dominated by GI symptoms
• Low discontinuation rates, similar to placebo
• No unexpected or new safety concerns, even at higher doses
• Sustained results, with weight returning only when treatment stopped

Clinical trials are only part of the picture. Since Mounjaro’s approval, real-world data and post-marketing surveillance by bodies like the MHRA and FDA continue to track the safety profile of Mounjaro.

So far, these findings are consistent with trial data:

• Most people tolerate Mounjaro well
• Certain risks require close attention, especially in people with underlying conditions
• Most of the risks are associated with counterfeit weight loss injections sold by unregulated services

The most common safety risks of Mounjaro are digestive problems such as:

• Nausea
• Vomiting
• Diarrhoea
• Constipation

These happen because Mounjaro slows down how quickly food leaves the stomach, which helps control appetite but can also upset the digestive system.

Some people may also experience mild bloating or stomach discomfort, especially when starting treatment or increasing the dose. These effects usually lessen as the body adjusts over time.

Although uncommon, serious risks are possible, which is why medical supervision is important.

Pancreatitis (Inflammation of the pancreas)

Mounjaro has been associated with rare cases of pancreatitis [1]. Anyone with a history of pancreatitis should discuss this risk with their prescriber and seek advice if they develop severe upper abdominal pain which radiates into the back.

Gallbladder problems

Significant weight loss, whether from lifestyle changes or medication, can increase the risk of gallstones or gallbladder inflammation. Symptoms include a sudden, intense abdominal pain in the upper right or centre of the abdomen, which can spread to the back or shoulder. This is not unique to Mounjaro but a potential risk, given the rapid rate of weight loss.

Thyroid tumours

Animal studies have shown an increased risk of thyroid tumours with this class of medication. While it’s unclear if this risk applies to humans, people with a personal or family history of medullary thyroid carcinoma (MTC) or MEN2 should not take Mounjaro.

Hypoglycaemia (low blood sugar)

On its own, Mounjaro rarely causes low blood sugar. But when used with other diabetes medications like insulin, the risk increases, so dose adjustments may be needed.

Gastrointestinal issues and kidney risks

Common effects like nausea or vomiting are usually mild but can lead to dehydration. In severe cases, this can put stress on your kidneys. Staying hydrated and monitoring kidney function is important, especially for those with pre-existing kidney disease.

Mounjaro may require additional medical supervision, or may not be suitable at all, if you:

• Have a history of pancreatitis
• Have history of gallstones or gallbladder disease
• Have severe kidney or liver disease
• Have a family history of MTC or MEN2
• Are pregnant or breastfeeding
• Have type 1 diabetes
• Are pregnant or planning to become pregnant (Mounjaro should be stopped 2 months before)
• Are breastfeeding
• Have an allergy to tirzepatide

Certain habits or health conditions can increase the safety risks associated with Mounjaro, including:

• Skipping meals or undereating can worsen nausea, vomiting, and increase the risk of low blood sugar.
• Not drinking enough water may lead to dehydration, which can place strain on your kidneys.
• Taking more than your prescribed dose or injecting more frequently than recommended increases the risk of side effects.
• Using other medications without checking first may be unsafe, as some drugs can raise the risk of low blood sugar or affect how your stomach functions.
• Using Mounjaro without a prescription is not recommended and may be unsafe.

• Use Mounjaro exactly as directed and do not change your dose or stop treatment without medical advice.
• Inject on the same day each week, at any time of day, with or without food.
• Do not use a higher dosage pen and try to inject a smaller amount to save money
• Rotate injection sites each week to reduce irritation or tissue changes.
• Ensure the liquid is clear and colourless, with no particles or cloudiness.
• Keep Mounjaro pens refrigerated (2°C–8°C) until use. Do not freeze or expose to direct heat or sunlight.
• Each pen is for single patient use only, even if the needle is changed.
• Seek medical advice if you experience severe gastrointestinal symptoms, signs of pancreatitis, or low blood sugar.
• Attend regular reviews to monitor your blood glucose, weight, and overall response to therapy.

Mounjaro is generally safe for most people when prescribed and monitored by a healthcare professional, and it is among the most effective treatments for weight loss available today.

While it has been thoroughly tested in clinical trials, it is not entirely risk-free.

Personalised care is key. Understanding your individual risk factors, following medical guidance, and staying alert to any unusual symptoms. With proper supervision, Mounjaro can be a safe and transformative part of your weight-management journey.