Who Should Not Take GLP-1 Medications?

GLP-1 medications such as Wegovy, Ozempic and Mounjaro have helped many people manage their weight or type 2 diabetes, but they are not suitable for everyone. Whether you're considering treatment privately or through the NHS, it's worth understanding who these medicines are not recommended for before you start.

This guide sets out the groups who should not take GLP-1 medications, the conditions that call for extra caution, and the questions worth raising with a prescriber before treatment begins.

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The short answer

GLP-1 medications aren't suitable if you're pregnant, trying to conceive, breastfeeding, or have a known hypersensitivity to the medicine. A personal or family history of certain thyroid cancers is treated as a significant caution by UK prescribers. Several other conditions, including pancreatitis, severe digestive problems, and advanced kidney or liver disease, call for closer monitoring rather than ruling treatment out outright. Your prescriber should ask about all of this before you start.

A quick recap on GLP-1 medications

GLP-1 receptor agonists, including semaglutide (Wegovy, Ozempic, Rybelsus) and the dual GIP/GLP-1 agonist tirzepatide (Mounjaro), work by mimicking a gut hormone that regulates appetite and blood sugar. They're licensed in the UK for type 2 diabetes and, at higher doses, for weight management in adults who meet specific BMI and health criteria.

Because they affect digestion, blood sugar and appetite regulation throughout the body, they're not appropriate for people with certain medical histories or in certain life stages.

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Who should not take GLP-1 medications

The following groups are generally advised against starting a GLP-1 medication:

People who are pregnant, trying to conceive, or breastfeeding. GLP-1 medications should not be used in pregnancy. For semaglutide, treatment should be stopped at least two months before trying to conceive, due to how long it stays in the body; other GLP-1 medications have shorter recommended washout periods, so this is worth confirming with your prescriber for the specific medicine involved. Breastfeeding is also generally advised against, as safety hasn't been established.
People with a known hypersensitivity to the active ingredient or any excipient. A previous allergic reaction to semaglutide, tirzepatide, or another GLP-1 medicine, or to any of the other ingredients in the pen or tablet, rules out that specific product.
Under-18s, outside of licensed exceptions. Wegovy has a licence for adolescents aged 12 and over with obesity in specific circumstances, but most GLP-1 weight management prescribing is for adults, and eligibility for younger patients is a specialist decision.
People with a personal or family history of medullary thyroid cancer, or multiple endocrine neoplasia type 2 (MEN 2). This isn't listed as a formal contraindication in the UK product information for semaglutide, but it's treated as a significant caution by UK prescribers because of thyroid tumours seen in animal studies, and it's a stated contraindication in some other markets. Anyone with this history should raise it before starting treatment.

Conditions that call for extra caution

These don't necessarily rule treatment out, but they mean closer monitoring, dose adjustment, or a more cautious conversation with a prescriber:

A history of pancreatitis. GLP-1 medications haven't been well studied in people who've previously had pancreatitis, and cases of acute pancreatitis, including rare serious ones, have been reported in people taking this class of drug. Persistent, severe abdominal pain should always be reported promptly.
Gastroparesis or severe digestive conditions. Because GLP-1 medications slow down stomach emptying, they can make gastroparesis symptoms worse and are not recommended if the condition is severe.
Diabetic retinopathy, for people with type 2 diabetes. Rapid improvements in blood sugar control have been linked to a temporary worsening of retinopathy, so people with existing eye complications from diabetes need closer monitoring.
Severe kidney or liver impairment. No dose adjustment is usually needed for kidney or liver impairment, but experience in severe cases is limited, and semaglutide is not recommended in end-stage kidney disease. Gastrointestinal side effects like vomiting and diarrhoea can cause dehydration, which is a particular concern if kidney function is already reduced.
A history of gallbladder disease. Rapid weight loss itself increases the risk of gallstones, and this risk has been observed in GLP-1 clinical trials.
Sudden or unexplained vision changes. A rare eye condition affecting blood supply to the optic nerve (non-arteritic anterior ischaemic optic neuropathy, or NAION) has been linked to semaglutide use in some studies. Anyone experiencing sudden or partial vision loss while on treatment should seek urgent eye assessment, and treatment is usually stopped if NAION is confirmed.
An upcoming general anaesthetic or procedure requiring sedation. Delayed stomach emptying has been linked to a higher risk of aspiration under anaesthesia, so anaesthetists and surgical teams usually need advance notice of GLP-1 use.
People on insulin or sulfonylureas. Combining these with a GLP-1 medication can increase the risk of low blood sugar, and doses may need adjusting when treatment starts.

Not meeting NHS funding criteria versus the medicine's licence

It's worth separating two thresholds that are easy to mix up. The UK licence for semaglutide and tirzepatide as weight management treatments covers adults with a BMI of 30 or above, or a BMI of 27 to 30 alongside a weight-related health condition such as high blood pressure, sleep apnoea or type 2 diabetes. This is the threshold a private prescriber assesses you against.

NICE's criteria for NHS funding are stricter than this. For semaglutide (Wegovy), NICE recommends NHS use, for a maximum of two years, within a specialist weight management service, for adults with a BMI of at least 35 alongside a weight-related condition, or a BMI of 30 to 34.9 who also meet the criteria for referral to specialist weight management services. For tirzepatide (Mounjaro), NICE recommends NHS use for adults with a BMI of at least 35 and a weight-related condition, without requiring a specialist service, which is why it's being rolled out through primary care as well. Both recommend a lower BMI threshold, usually by 2.5 kg/m2, for people from south Asian, Chinese, other Asian, Middle Eastern, Black African or African-Caribbean backgrounds, reflecting the higher health risks seen at a lower BMI in these groups.

Falling outside NICE's thresholds doesn't mean a GLP-1 medication is medically unsafe for you, it means you fall outside the criteria for NHS funding specifically. Many people who meet the medicine's licensed criteria but not NICE's stricter NHS threshold access treatment privately instead, where a prescriber assesses against the licence and any contraindications, not the NHS funding criteria.

What to raise with your prescriber

Before starting a GLP-1 medication, whether via the NHS or a private or online prescriber, it's worth being upfront about:

Any personal or family history of thyroid cancer or MEN 2
Current or planned pregnancy, or breastfeeding
A history of pancreatitis, gallbladder disease, or severe digestive conditions
Diabetes-related eye or kidney complications
All current medications, including insulin, sulfonylureas, and oral contraceptives
Any upcoming surgery or procedures requiring anaesthesia

A responsible prescriber, NHS or private, should ask about these before writing a prescription. If you're offered a GLP-1 medication online without any of this being discussed, that's worth treating as a red flag.