This article is provided for general information purposes only and does not constitute medical advice. I am not a medically qualified professional, and the content should not be relied upon as a substitute for professional medical guidance. Always consult a GP or healthcare provider before starting any medication or weight management programme.
Is Mounjaro Safe?
Mounjaro (tirzepatide) is rapidly gaining attention in the UK as a groundbreaking weekly injection for both type 2 diabetes and weight management. With compelling results in clinical trials, patients and clinicians alike are asking if Mounjaro is safe?
This article explores the safety profile of Mounjaro, based on findings from clinical research, regulatory reviews in the UK by the MHRA and in the US by the FDA, along with real-world use. If you’re considering this treatment, and have questions, here’s what you need to know.
What Is Mounjaro?
Mounjaro is the brand name for tirzepatide, developed by Eli Lilly & Co. It’s the first medicine to activate both GIP (glucose-dependent insulinotropic polypeptide) and GLP-1 (glucagon-like peptide-1) receptors, which are the two hormones that help regulate appetite, insulin release, and digestion.
Originally approved in May 2022 by the FDA for type 2 diabetes, Mounjaro has since received MHRA approval for weight loss and weight management in the UK, granted on 8 November 2023.
The full history of Mounjaro, its timeline and background to Eli Lilly & Company can be found in this article.
Why Was Mounjaro Approved?
The MHRA and FDA based their decisions on strong results from clinical trials. In particular, the SURMOUNT and SURPASS programmes demonstrated:
- HbA1c reductions of up to 2.4 percentage points
- Weight loss of up to 22.5% of total body weight
- Better outcomes than semaglutide (Ozempic/Wegovy) and long-acting insulin
These outcomes were achieved through a combination of the Mounjaro metabolic effects; appetite suppression, and slowed gastric emptying, all contributing to sustained weight reduction and blood sugar control.
How Does Mounjaro Work?
Mounjaro mimics two naturally occurring gut hormones:
- GIP helps enhance insulin secretion and reduce glucagon after eating
- GLP-1 delays gastric emptying and suppresses appetite in the brain
The combined action of these pathways leads to improved glucose regulation, reduced food intake, and weight loss, more effectively than GLP-1 alone.
What Are the Common Side Effects of Mounjaro (tirzepatide)?
Most side effects of Mounjaro are mild and gastrointestinal in nature, especially during the early dose titration stages. The most frequently reported side effects include:
- Nausea
- Diarrhoea
- Constipation
- Vomiting or indigestion
- Loss of appetite
These side effects tend to resolve over time, particularly if the dose is increased gradually as per medical guidance, which varies from one patient to another, and is important to listen to professional advice..
Are There Any Serious Risks?
In rare cases, Mounjaro may cause more serious side effects, including:
- Pancreatitis (inflammation of the pancreas)
- Gallbladder issues
- Thyroid C-cell Tumours – seen in animal studies, but not yet confirmed in humans (correct at the time of publishing)
- Severe Hypoglycaemia when combined with insulin or sulfonylureas
The MHRA and FDA both include warnings about the theoretical risk of thyroid cancer, advising that Mounjaro should not be used by patients with a personal or family history of medullary thyroid carcinoma (MTC) or MEN 2. If you have any concerns, consult your GP or a qualified medical practitioner.
Who Should Not Take Mounjaro?
- Anyone with a history of MTC or MEN 2
- People with known allergies to tirzepatide or formulation ingredients
- Pregnant or breastfeeding women
- Those with severe gastrointestinal disorders
Additional Safety Considerations
- Start low, go slow: Mounjaro should be initiated at 2.5 mg weekly and increased gradually to minimise any potential side effects.
- Monitoring is essential: Regular checks for blood glucose, kidney function, and body weight are recommended.
- Contraceptive caution: Mounjaro may reduce the effectiveness of oral contraceptives. A backup method (eg. condom) is advised for 4 weeks after starting or increasing the dose.
Reporting and Long-Term Data
The MHRA encourages all patients to report suspected side effects via the Yellow Card Scheme. In the US, adverse reactions are monitored through the FDA’s FAERS system.
Additional long-term safety data are expected from the ongoing SURPASS-CVOT study, a major cardiovascular outcomes trial due to complete in 2026.
Conclusion: Is Mounjaro Safe?
For most eligible adults, Mounjaro has a favourable safety profile when used as prescribed. While mild digestive issues are common, serious risks are rare. However, patients with thyroid conditions, pancreatitis, or certain genetic syndromes should not take it.
As with any medication, it’s essential to consult a healthcare professional before starting Mounjaro to ensure it’s appropriate for your circumstances.
We have a number of articles on this topic, specifically aimed at cyclists, so check them out of you’re looking for more info; Cycling on Mounjaro and Exercising on Mounjaro
Disclaimer: This article is provided for general information only and does not constitute medical advice. I am not a medically qualified professional. Always seek personalised advice from a doctor or licensed prescriber before starting or stopping any medication.
