Who is not suitable for weight loss injections

What the licensed criteria and regulatory guidance rule out absolutely

The SmPCs for both Mounjaro (tirzepatide) and Wegovy (semaglutide) (the documents that set the legal boundaries of prescribing) specify a number of absolute contraindications. The clearest is a personal or family history of medullary thyroid carcinoma (MTC), a rare form of thyroid cancer. Related to this, anyone with Multiple Endocrine Neoplasia type 2 (MEN2) must not use either medicine; this is a genetic syndrome that dramatically raises lifetime MTC risk, and GLP-1 receptor agonists have shown thyroid C-cell changes in animal studies. These are hard stops, not matters for clinical discretion.

A serious hypersensitivity reaction to the active substance or any excipient is a second absolute bar. If someone has previously had an anaphylactic or severe allergic response to tirzepatide or semaglutide, re-exposure is not appropriate.

The NHS's guidance on weight management injections also flags that people with a history of pancreatitis should discuss this carefully with their prescriber before starting. Pancreatitis is not automatically a hard contraindication in all cases, but it is a significant precaution, anyone with prior episodes needs careful individual assessment. The MHRA's January 2026 Drug Safety Update reinforced that acute pancreatitis is a recognised, potentially serious effect of this drug class, and prescribers take prior history seriously.

People under 18 are outside the licensed indication for both medicines, as are those with type 1 diabetes, for whom neither Mounjaro nor Wegovy is approved. If you are considering your options and want to understand the full eligibility picture, our page on who qualifies for a weight loss injection covers the positive criteria in depth.

Pregnancy, breastfeeding, and planning a family

This is one of the most commonly asked-about contraindications, and the guidance is unambiguous. Neither tirzepatide nor semaglutide is recommended during pregnancy or breastfeeding. Animal studies have raised concerns about developmental effects at therapeutic doses, and because there is no adequate safety data in human pregnancy, prescribers will not issue a prescription to someone who is pregnant or nursing.

Trying to conceive sits in the same category. The MHRA advises using effective contraception while on these medicines. For tirzepatide specifically, there is an additional point that many people miss: women taking oral contraceptive pills should use a barrier method for the first four weeks of treatment and for four weeks after each dose increase, because the slowing of gastric emptying can reduce pill absorption during that window. This does not appear to apply to semaglutide to the same degree, but the contraception conversation belongs in every consultation for women of childbearing age. NHS England's guidance on weight management injectable medicines covers this clearly.

A wash-out period before trying to conceive is also recommended; the exact duration should be confirmed with your prescriber. This is not a minor administrative note, it is a patient-safety requirement.

If you carry your medication routine into everyday life (some patients keep a pen at the back of the fridge, others set a reminder linked to their morning coffee), it is worth building the stop-date into that routine well in advance of any planned pregnancy.

Conditions that require careful prescriber assessment, not automatic exclusion

Some circumstances sit between an absolute bar and a straightforward green light. They do not automatically disqualify someone but do require the prescriber to weigh the balance of risk and benefit carefully, and in some cases to decline.

Severe gastrointestinal conditions (including gastroparesis and inflammatory bowel disease in an active flare) are among these. GLP-1 medicines slow gastric emptying, which can worsen gastroparesis significantly. Likewise, anyone with a history of severe, persistent GI illness that required hospitalisation needs to have a frank conversation with a clinician before starting.

Gallbladder disease is another. Rapid weight loss of any kind can precipitate gallstones, and GLP-1 use appears to carry a modestly elevated gallbladder risk. A history of gallstones or cholecystitis does not automatically exclude someone, but it is factored in.

Certain kidney conditions matter too. Severe dehydration from GI side effects (vomiting, diarrhoea) can worsen existing renal impairment; prescribers take baseline kidney function into account. Severe hepatic impairment requires similar consideration, though it is less frequently a limiting factor in practice.

Finally, certain drug interactions warrant attention. If you take other medicines that affect blood glucose, including sulfonylureas or insulin, the combination needs prescriber oversight to manage hypoglycaemia risk. This is not unique to GLP-1 medicines, but it is one reason a thorough medicines review at consultation matters. Understanding the full range of what injectable weight loss treatments involve before you apply means fewer surprises at the assessment stage.

When a prescriber declines, and what that means in practice

It is worth naming this plainly: a responsible prescriber will sometimes say no. That is the system working correctly, not a failure. The GPhC expects Independent Prescribers to use clinical judgement at every consultation, and at nume every application is read by a named clinician rather than processed automatically.

If you have been declined elsewhere, or if you are unsure whether your history makes you unsuitable, the consultation is the right place to raise it. Our clinical team can discuss the specific factor that gives you pause and explain what, if anything, changes it. Sometimes a contraindication is absolute; and our detailed guidance on who should not take weight loss injections can help you understand where your circumstances sit before you speak to a prescriber.

For a broader overview of available routes, the weight loss treatment options page outlines what is licensed in the UK and how the medicines differ from one another. People comparing options also find the guide on choosing between injectables a useful starting point before deciding whether to apply, and our weight loss injectable page covers how these medicines work in practice for those who want a thorough grounding before their consultation. For general questions about the process, our FAQs cover the consultation and aftercare in detail.

If you have read through this page and believe you may be eligible, you can speak to our prescribers through a free consultation, same-day clinical review, no waiting list, and a straight answer on suitability.