Who can't have weight loss injections — and why the rules exist

The biggest misconception: that failing the BMI cut-off is the main reason people can't use these medicines

Most people searching this question assume the answer is about body weight — that weight loss injections are only off-limits because someone's BMI is too low. That's understandable; eligibility criteria get a lot of coverage. But BMI is a threshold for access, not the reason these medicines are clinically unsuitable. The real contraindications are medical, not numerical.

Both Mounjaro and Wegovy have a set of absolute contraindications, situations where the medicine should not be used regardless of BMI. There is also a larger group of conditions that don't automatically rule treatment out but do require a prescriber to think carefully. Getting these right is exactly why clinical assessment exists. If you want to understand the eligibility picture from the other direction, our page on who does qualify covers the licensed criteria in full.

So: the most important question isn't "is my BMI high enough", it's "is there anything in my medical history that changes the risk profile of this treatment?" That's what the sections below address.

Situations where weight loss injections are not recommended or not licensed

Pregnancy, breastfeeding, and trying to conceive. UK guidance is clear: GLP-1 receptor agonist medicines are not recommended during pregnancy or while breastfeeding, and women who are actively trying to conceive should not use them. The MHRA advises that effective contraception should be used throughout treatment and for a wash-out period afterwards before attempting conception. This is one of the first things a prescriber checks. If your situation changes during treatment, contact your prescriber promptly, don't simply leave the pen in the fridge door and carry on.

Under-18s. Neither Mounjaro nor Wegovy holds a UK licence for weight management in people under 18. A prescriber cannot legally issue a prescription for this indication in that age group.

Medullary thyroid carcinoma and MEN2. A personal history of medullary thyroid carcinoma (MTC), or a family history of it, is listed as a contraindication in the prescribing information for both medicines. The same applies to Multiple Endocrine Neoplasia type 2 (MEN2). This is a non-negotiable exclusion, not a discussion point. The NHS patient information page for tirzepatide lists the conditions you should tell a prescriber about before starting.

Severe gastrointestinal disease. Gastroparesis (delayed gastric emptying) and other significant GI motility disorders can interact with the way these medicines slow digestion, and prescribers are cautious. Inflammatory bowel disease and previous bowel surgery are also flagged for discussion.

Pancreatitis history. Both medicines are associated with an infrequent but serious risk of acute pancreatitis. In January 2026, the MHRA issued a Drug Safety Update specifically highlighting this risk for GLP-1 medicines and reinforcing the importance of stopping treatment and seeking urgent care for severe, persistent stomach pain that radiates to the back. Anyone with a history of pancreatitis needs a careful prescriber conversation before starting, this is not a blanket ban in all cases, but it warrants real scrutiny.

Conditions that need extra care, not automatic exclusion

A number of situations don't rule these medicines out but do change how a prescriber approaches the consultation. Diabetic retinopathy, for example, can worsen with rapid changes in blood glucose, relevant mainly where someone has type 2 diabetes alongside a weight-management prescription. Kidney function matters too: severe renal impairment affects how some medicines behave, and a prescriber will review this.

People on certain other medications also need individual assessment. For those taking oral contraceptives alongside Mounjaro specifically, NHS England's guidance on weight management injections advises adding a non-oral method of contraception for the first four weeks of treatment and for four weeks after each dose increase, because tirzepatide slows gastric emptying in a way that may reduce pill absorption. Semaglutide does not carry the same documented interaction, but the precaution is worth raising with a prescriber regardless.

Heart rate: both medicines can cause a small increase in resting heart rate, which is a consideration in people with certain cardiac arrhythmias. Eating disorders with active restriction are also approached with particular care, a prescriber will ask about this, because appetite suppression in that context carries different risks. If you have questions about a specific situation not covered here, our frequently asked questions page covers a range of circumstances, or you can get in touch with our team directly.

Why a clinical review exists, and what happens when a prescriber says no

These contraindications and cautions are exactly why these medicines require a prescription. An algorithm reading a BMI score cannot ask whether you had pancreatitis three years ago, whether you're on the combined pill, or whether you're planning a pregnancy. A real prescriber can, and at nume, every consultation is read by a GPhC-registered Independent Prescriber on the same day it is submitted, not passed through automated scoring.

If a prescriber determines that treatment isn't suitable, that is a clinical decision made in your interest. It is not always permanent: some situations change (a resolved pregnancy, a condition brought under control), and our page on why a prescription might be declined explains the common reasons and what the options might be. For context on what the private route involves and what a transparent price covers, the cost breakdown for weight loss injections is worth reading before you decide whether to proceed.

Weight management is a clinical area, not a consumer product category. The rules around who these medicines aren't suitable for exist because the medicines are powerful and the consequences of using them in the wrong situation can be serious. If you're unsure whether your circumstances make you a candidate, our guide to whether you can have weight loss injections is a useful starting point, and if you want a fuller picture of who can use weight loss injections based on medical and lifestyle factors, that page sets out the detail alongside the clinical criteria for who can get weight loss injections through a regulated UK service. If you think you may be suitable and want a qualified clinician to assess your specific history, you can start a free consultation with our prescribers today.