The UK government has announced that GPs in England will receive bonuses of up to £3,000 per year to increase prescriptions of Mounjaro (tirzepatide), the NHS-approved weight loss injection.
The UK government has a new plan: pay GPs up to £3,000 a year in bonuses to prescribe Mounjaro, a weekly weight loss injection, and an extra £1,000 for referring patients to weight loss programmes. With £25 million behind it, the scheme rolls out in April 2026.
The idea is to make the drug available based on medical need, not wealth — since many people are already paying privately for it. But the announcement has stirred controversy, with doctors’ groups warning about inequality and already-stretched workloads.
And beyond the politics, there’s a more pressing question: is this drug actually safe?
Here’s what the science says.
So what is Mounjaro?
Mounjaro (tirzepatide) was originally developed for type 2 diabetes and was eventually approved for weight loss. In clinical trials, patients lost around 20% of their body weight over 72 weeks — which is genuinely impressive.
Currently, you need a BMI of 40 or above (or 37.5 for some ethnic groups) plus at least four obesity-related health conditions to qualify. From April, that threshold drops to BMI 35, potentially opening the door to around 220,000 more patients by 2028.
The side effects most people experience: stomach trouble
The most common complaints are digestive — nausea, vomiting, diarrhoea, constipation, and stomach pain. These aren’t rare blips. A 2025 analysis of the US drug safety database found nearly 66,000 adverse event reports for tirzepatide between 2022 and early 2025, with digestive problems making up the largest share.
UK data tells a similar story: 65% of side effects reported to the MHRA in 2025 were gastrointestinal. Most weren’t classed as serious, but still made up 43% of serious outcomes and 55% of reports linked to a fatal outcome. In other words, what starts as an upset stomach can, occasionally, become something much more dangerous.
Pancreatitis: rare but serious
In October 2025, Mounjaro’s maker Eli Lilly updated the drug’s leaflet to include an explicit warning about acute pancreatitis — a painful and potentially life-threatening inflammation of the pancreas. The update tells patients to stop the drug immediately and seek urgent help if they experience severe, persistent abdominal pain. Anyone with a history of pancreatitis should talk to their doctor before starting it.
Vision loss: an alarming emerging risk
This is perhaps the most worrying development to come out of real-world use. A 2025 study in JAMA Ophthalmology found a link between tirzepatide and a condition called NAION — essentially an optic nerve stroke that can cause permanent vision loss. Researchers think the drug’s rapid correction of blood sugar may cause the optic nerve to swell.
This wasn’t a one-off finding. An earlier 2024 study found a similar risk across the whole class of GLP-1 drugs. By late 2025, two more studies had confirmed worse vision outcomes over two years in patients taking these medications. In the US, legal action has already begun.
Gallstones and thyroid concerns
Rapid weight loss is a well-known trigger for gallstones, and Mounjaro is no exception. In clinical trials, gallbladder disease occurred in 0.6% of patients taking the drug, compared to 0% in the placebo group.
There’s also a black-box warning — the most serious type the FDA issues — about thyroid tumours. Animal studies showed a clear link between the drug and thyroid cancer in rats. It’s not yet known whether the same applies to humans, but the drug is not recommended for anyone with a personal or family history of certain thyroid cancers.
Wrong doses: the biggest safety signal of all
Here’s a finding that doesn’t get enough attention: the single most reported problem with tirzepatide in the US safety database isn’t nausea or pancreatitis — it’s patients being given the wrong dose. Reports of dosing errors grew nearly eightfold between 2022 and 2024, reaching almost 10,000 cases.
This matters enormously as prescribing is scaled up rapidly. Without proper patient education and careful monitoring, errors will multiply.
What about pregnancy, older patients, and children?
Women hoping to get pregnant are advised to stop Mounjaro at least two months beforehand, as animal studies suggest it may harm fetal development. Women on the pill should also switch contraception temporarily, as the drug slows digestion and can make the pill less effective.
Older patients tend to be more sensitive to the drug’s effects, and its safety in children under 10 hasn’t been established.
So should we be worried?
None of this means Mounjaro is a dangerous drug that shouldn’t be prescribed. For people with severe obesity, the health benefits — reduced risk of heart disease, diabetes, and early death — are real and well-evidenced. For the right patients, it can be life-changing.
But this is a powerful drug with a safety profile that is still evolving. Some of the most serious risks, like vision loss, only came to light years after it was approved, through real-world use. And the biggest safety warning in the global database is about patients being given the wrong dose.
Paying GPs bonuses to maximise prescriptions creates pressure to prescribe quickly rather than carefully. Rushed consultations mean less time for thorough screening, checking for contraindications, and setting up proper monitoring — exactly what this drug requires.
The bottom line
Mounjaro is a genuine breakthrough in treating obesity. But it comes with real risks that deserve real attention. Making it more widely available is a worthy goal — but only if that rollout comes with proper patient education, regular check-ins, and enough GP time to do the job properly.
Bonuses without safeguards don’t just cut corners. They could turn a promising treatment into a public health problem.
Scientific Sources
NIH PubMed Central Alsulami et al. (2025). Real-World Safety Concerns of Tirzepatide: A Retrospective Analysis of FAERS Data (2022–2025). Healthcare, 13(18), 2259. PMC12469573.
Jama Network JAMA Ophthalmology (2025). Tirzepatide and nonarteritic anterior ischaemic optic neuropathy (NAION).
Jama Network JAMA Ophthalmology (2024). GLP-1 receptor agonists and NAION risk in type 2 diabetes patients.
The Pharmaceutical Journal The Pharmaceutical Journal (November 2025). ‘Life-threatening condition’ added to Mounjaro patient information leaflet.
Science Direct Safety profile of tirzepatide: A real-world pharmacovigilance analysis of EudraVigilance database
This blog post is for informational purposes only and does not constitute medical advice. Always consult a qualified healthcare professional before starting or stopping any medication.
