Who should not take weight loss injections — and why it matters

You've been told Mounjaro or Wegovy might help, but something in your history gives you pause

This is a familiar starting point. Someone's GP has mentioned weight loss injections, or they've read about the results, and they're interested. Then they remember a thyroid scare years ago, or a bout of pancreatitis, or the fact they're hoping to start a family soon. Those hesitations are worth taking seriously.

Tirzepatide and semaglutide work by mimicking gut hormones that regulate appetite and blood sugar. That mechanism is effective, but it also means the medicines interact with systems throughout the body. A clear picture of who qualifies requires an equally clear picture of who does not.

The NHS medicines information for tirzepatide sets out several categories of people for whom treatment is not recommended or is outright contraindicated. At the top of that list: anyone who has had, or whose close family members have had, medullary thyroid carcinoma or Multiple Endocrine Neoplasia type 2. These are rare conditions, but the thyroid signal from animal studies in this drug class means prescribers treat the history seriously. You'll be asked directly.

Pancreatitis is another firm stop. The MHRA's Yellow Card scheme is the route for reporting suspected reactions, and the regulator's January 2026 Drug Safety Update specifically flagged acute pancreatitis as a known, infrequent but potentially serious effect of GLP-1 medicines. Anyone with a current episode or a recent history of acute pancreatitis would not receive a prescription without thorough clinical review.

Life stages where neither injection is recommended

Pregnancy sits at the top of this list. Neither Mounjaro nor Wegovy is recommended during pregnancy, while breastfeeding, or in the weeks before trying to conceive. The NHS guidance on weight management injections advises using contraception throughout treatment and for a defined period afterwards before attempting conception. For tirzepatide specifically, there is an added consideration for people on oral contraceptive pills: the pill's absorption may be reduced during the first four weeks of treatment and for four weeks after each dose increase, so a non-oral method such as condoms should be added during those windows.

This is not a minor caveat. It affects real family planning decisions, and our prescribers discuss it properly rather than burying it in a leaflet. If you're considering your options and the timing of treatment matters to you, it's worth stepping back to consider whether weight loss injections are the right choice for you at this point in your life before you start.

Under-18s are not candidates for either medicine for weight management. The licensing is unambiguous: these treatments are for adults only. If you're enquiring on behalf of a younger family member, the right conversation is with their GP or paediatric team.

Medical conditions that shift the risk-benefit balance

Beyond the absolute contraindications, several conditions move a prescription into a detailed clinical conversation rather than a straightforward yes or no. Severe kidney disease, serious gastrointestinal conditions such as gastroparesis or inflammatory bowel disease, and certain eating disorders all require careful thought. The concern with GI conditions is partly practical: nausea and vomiting are among the most common early side effects, and in someone with an already-compromised digestive system, that added burden can become significant.

Eating disorders deserve particular care. GLP-1 medicines reduce appetite markedly, and for someone with a current or recent history of restrictive eating, that effect may interact with existing patterns in ways that are hard to predict. A prescriber would want to understand the full picture before proceeding. If this applies to you, Beat, the UK's eating disorder charity, provides support and guidance that sits alongside any clinical conversation.

Diabetic retinopathy is another condition flagged in prescribing information for semaglutide: rapid changes in blood sugar control can affect the eyes, so anyone with active or poorly-controlled diabetic eye disease would be assessed with particular attention.

A full overview of how weight loss injections work sets the mechanism in context if you're still forming a view. And if cost is part of your thinking, what private treatment actually includes is worth understanding before comparing headline prices.

What happens if you're unsure about your own situation

Most people who fill in our consultation form have already Googled their own condition and found partial answers. The honest reality is that many of the questions above don't have a blanket answer: they depend on the specifics of your history, how well-controlled a condition is, and what other medicines you take. That's precisely what a prescriber is for.

At nume, every consultation is read by a GPhC-registered Independent Prescriber on the same day, a real clinician, not automated software. If your history raises a question, they'll ask it. If something in your picture means treatment isn't right for you, they'll say so. You can verify our pharmacy registration at the GPhC register (registration number 9012878).

If you'd like to look at the broader landscape of options before deciding anything, our weight loss treatment overview covers what's available for different situations. And if you have questions before starting a consultation, our FAQs cover the ones we hear most often, including how long you should expect to stay on treatment before you see lasting results. When you're ready, check your eligibility with a free consultation and let a prescriber give you a straight answer based on your actual health.