Is Mounjaro Safe? Side Effects & Long-Term Use Risks

Mounjaro is a once-weekly injectable medication that contains the active ingredient tirzepatide. It’s approved in the UK to help manage blood sugar levels in type 2 diabetes and promote weight loss in overweight or obese people.

Safety concerns surrounding Mounjaro are on the rise due to reports of misuse, including illegally getting the medication without a prescription, ignoring the dosage schedule, or use by individuals who do not meet the prescribing guidelines. There are also some concerns about the long-term safety of using weight loss medications, like Mounjaro.

In this guide, we will address the common safety concerns surrounding Mounjaro, including who should and should not use it, explore potential side effects, and discuss the possible long-term risks associated with tirzepatide.

Yes, Mounjaro is generally considered safe when used correctly and under medical supervision. Despite being relatively new for weight loss, Mounjaro has been used long-term as a diabetes treatment – the original purpose for glucagon-like peptide-1 (GLP-1) agonists.

The first GLP-1 medication for diabetes was approved in 2006, while Saxenda, now Nevolat, was approved in 2014 for weight loss, followed by Wegovy. Although they’re different medications, they all mimic the effects of the natural hormone GLP-1, helping you to lose weight by:

• reducing appetite
• slowing gastric emptying
• improving insulin sensitivity

Mounjaro is the only dual-agonist as it mimics GLP-1 and gastric inhibitory peptide (GIP), which is thought to further enhance these effects and improve weight loss results.

Studies into Mounjaro's safety

For Mounjaro, being approved as a weight loss medication means it has undergone rigorous clinical testing to assess its safety and efficacy.

Tirzepatide, the active ingredient in Mounjaro, was first studied in more than 6,200 type 2 diabetes patients as part of the SURPASS clinical trial program. In total, there were 5 trials (SURPASS 1 to 5). It was found to help blood glucose levels return to normal in up to 62% of people treated with the highest dose of 15mg per week, but participants were also losing weight. This led to the SURMOUNT trials, where Mounjaro was assessed for its benefits on weight loss.

Several SURMOUNT trials have been carried out since 2022. The first study demonstrated that, at the maximum maintenance dose over 72 weeks, the average weight loss was 22.5%. The study also concluded that there were no major safety concerns, with the most common side effects being mild to moderate gastrointestinal events.

These extensive studies and their results helped confirm that Mounjaro is a safe and effective treatment, leading to the Medicines and Healthcare products Regulatory Agency (MHRA) approval of its use for weight loss in 2023.

The best way to ensure the safety of Mounjaro is to take it exactly as it is prescribed.

Before you start treatment, a doctor must assess your suitability and ensure you are eligible for treatment. To get a prescription for Mounjaro from Superdrug Online Doctor, you must have a body mass index (BMI) of:

• 30kg/m2 or more (obese)
• 27kg/m2 or more (overweight) and a weight-related health issue such as high blood pressure

Everyone must start on the lowest 2.5mg per week dose and slowly titrate up (increase the dose) to allow your body to get used to the active ingredient and reduce the chance of side effects. For example, here is what a typical Mounjaro treatment journey looks like:

Any medication can cause side effects, including Mounjaro. By following the dosage schedule and taking it exactly as prescribed, you can lower the chances of getting them. The most common Mounjaro side effects are usually mild and improve as your body gets used to the medication.

Common Mounjaro side effects include:

• feeling sick (nausea)
• diarrhoea
• being sick (vomiting)
• stomach pain
• constipation

However, there are some less common but more serious side effects. They are:

• pancreatitis, or an inflamed pancreas (can affect up to 1 in 100 people) – causes severe stomach and back pain that does not go away
• severe allergic reactions (affects up to 1 in 1,000 people and is a medical emergency) – includes symptoms such as breathing or swallowing difficulties, and rapid swelling of the lips, tongue, or throat

There are some serious risks and warnings associated with Mounjaro, and it’s important to understand these before starting treatment. These effects are also possible if you take Mounjaro when you do not need it, and in the most severe cases, they can be life-threatening. These serious risks are:

Thyroid tumours

In pre-clinical studies in rats only, tirzepatide caused thyroid C-cell tumours. There have been no cases of thyroid cancer linked to this drug in humans.

The relevance for humans is considered to be low, but cannot be completely excluded. If you develop any of the following symptoms, speak to your GP straight away:

• a lump or swelling in the neck
• hoarseness
• swallowing issues
• shortness of breath

Low blood sugar

Mounjaro lowers blood glucose levels (hypoglycaemia), especially if you are taking any other diabetes medications. Symptoms can include:

• headache
• drowsiness
• weakness
• confusion

Your doctor may reduce the dose of your other diabetic medications before starting Mounjaro.

Pancreatitis

An inflamed pancreas is an uncommon side effect of GLP-1 agonists, including Mounjaro. It can affect up to 1 in 100 people and causes symptoms such as severe pain in the stomach and back, which does not go away. If you experience any of these symptoms, you should contact your doctor straight away.

Gallbladder problems

An uncommon side effect of Mounjaro, affecting up to 1 in 100 people, is cholecystitis or an infection of the gallbladder. It has been found in people who are prescribed Mounjaro for weight loss and can cause symptoms such as intense pain in the upper abdomen, yellowing of the skin (jaundice), and a fever.

Kidney function changes

There have been some reports of Mounjaro affecting kidney function through the gastrointestinal side effects it can cause, such as feeling or being sick or diarrhoea, which can lead to dehydration. It’s important to monitor yourself for signs of dehydration, especially if you get any of these side effects and drink plenty of fluids throughout your treatment.

Who should avoid taking Mounjaro for weight loss?

You should tell your doctor before taking Mounjaro if you:

• are allergic to tirzepatide or any other ingredients (do not take Mounjaro)
• have severe problems with digesting food or food remains in your stomach for longer than normal
• have ever had pancreatitis
• have eye problems such as diabetic retinopathy or macular oedema
• are using a sulphonylurea or insulin to manage diabetes

Most people who meet the prescribing guidelines for Mounjaro find that it’s a safe and effective treatment. However, it’s not suitable for everyone.

Despite its approval, Mounjaro is still a relatively new weight loss medication, and long-term safety data is limited.

The National Institute for Health and Care Excellence (NICE) states that if you have not lost at least 5% of your starting body weight within 6 months of starting Mounjaro, you should consider stopping, as it may not be working for you.

Following this guidance also ensures that you are not taking the medication unnecessarily and reduces the risk of any long-term health concerns that may arise in the future.

You can minimise the chance of side effects and ensure you are taking Mounjaro safely and properly by:

✓ only requesting it from reputable and regulated online services

✓ making sure you get it with a prescription from a licensed doctor or healthcare professional

✓ always following your doctor's instructions and advice when taking it

✓ starting with the lowest dose and titrating up slowly (at least every 4 weeks until you reach the maintenance dose)

✓ staying hydrated, especially during the first few weeks and if you experience side effects

✓ monitoring any new or worsening symptoms, and contacting your doctor if you are concerned

✓ injecting your medication at the same time each week

✓ avoiding combining Mounjaro with other GLP-1 medications

✓ following lifestyle changes, such as diet and exercise plans

Compared to other weight loss injections, like Wegovy and Nevolat, Mounjaro has shown the most significant weight loss results. It’s believed that this is because Mounjaro has a dual action by binding to both GLP-1 and GIP receptors, enhancing its appetite suppression effects.

However, individual tolerance and side effects can vary from person to person. Find out more about the ways Mounjaro, Wegovy, and Nevolat compare in this table:

Are weight loss injections safer than weight loss tablets?

Weight loss injections often result in more significant weight loss than pills, but both can have side effects, and neither is safer than the other. The safety of injections or pills will depend on any underlying health conditions you have, current medication, and how your body responds to the active ingredients.

Weight loss pills, like orlistat, Xenical, and Mysimba, require a prescription from a doctor before you can obtain them. They will assess your suitability to make sure they are safe for you to take.

alli, an over-the-counter orlistat pill, can be purchased without a prescription, but a pharmacist will ask you some medical questions to make sure that it is suitable for you to take.

When taken as prescribed, Mounjaro is safe for weight loss. Yet, like all medications, it can cause side effects, most of which are mild and will go away as your body gets used to Mounjaro.

The long-term safety of using GLP-1 agonists to help you lose weight, including Mounjaro, is not fully known because the current evidence is limited. However, current clinical trials have not identified any serious adverse effects.

If you are worried about any adverse events or are currently experiencing Mounjaro side effects that are causing you concern, it’s important to speak to your doctor for further advice.

Does Mounjaro affect your kidneys?

Yes, Mounjaro can indirectly affect kidney function, mainly through dehydration caused by being sick or having diarrhoea. If you are using Mounjaro, you should stay hydrated and contact your doctor if you’re concerned or have any existing kidney issues.

Is Mounjaro safe to take for weight loss if you don’t have diabetes?

Yes, Mounjaro has been approved for weight loss in the UK, even for people who do not have diabetes. You will need to meet specific prescribing guidelines to get it privately: a BMI of over 30, or over 27 with one or more weight-related conditions.

The NHS has its own set of prescribing guidelines and is currently focused on providing Mounjaro to those most ‘in need’.

Which is safer, Mounjaro or Ozempic?

Both Mounjaro and Ozempic are GLP-1 agonists and have similar safety profiles. They can also cause similar side effects. However, Mounjaro is available for both weight loss and diabetes treatment, while Ozempic is licensed to manage type 2 diabetes in the UK.

Is it safe to take Mounjaro while pregnant?

No, it’s not safe to use Mounjaro while you are pregnant. It’s not known if tirzepatide can affect your unborn child. If you are, think you might be, or are planning to get pregnant, tell your doctor before taking Mounjaro.

Is Mounjaro safe to take while breastfeeding?

No, it’s not recommended to use Mounjaro while you are breastfeeding because it is not known if tirzepatide passes into breast milk.

Does Mounjaro lower blood sugar in non-diabetics?

Yes, Mounjaro can lower blood sugar levels and improve insulin resistance, even in people without diabetes. This is one of the ways it can help support weight loss, and is also one of the reasons why your doctor will monitor your treatment and response carefully.