Before you start any prescription weight loss injection, it is essential to know who should not take GLP-1 medicines. Drugs such as Wegovy, Ozempic, Mounjaro, Zepbound and Saxenda help many adults lose weight and improve metabolic health, but they are not safe for everyone. Some people must avoid them completely (contraindications), and others can use them only with extra caution or monitoring (warnings and precautions). This guide explains both groups in plain language, the reasons behind the rules and how a prescriber checks your suitability.
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It is general information and does not replace the patient information leaflet or your clinician’s advice. If anything below applies to you, discuss it openly in your consultation.
In This Guide
- Absolute Contraindications: Who Should Not Take GLP-1 Medicines
- Conditions Needing Caution or Specialist Advice
- Who Should Not Take GLP-1 for Weight Loss Based on BMI or Age?
- Medicines That Can Interact With GLP-1 Treatment
- Warning Signs to Stop and Seek Urgent Help
- How a Prescriber Checks Your Suitability
- What If You Are Not Eligible?
- Never Use Unregulated Products to Get Around the Rules
Absolute Contraindications: Who Should Not Take GLP-1 Medicines
1. Personal or family history of medullary thyroid carcinoma (MTC)
Semaglutide, tirzepatide and liraglutide carry a boxed warning because they caused thyroid C-cell tumours in rodents. It is unknown whether they cause these tumours or medullary thyroid carcinoma in humans, so they are contraindicated in anyone with a personal or family history of MTC. The warning also covers symptoms to report, such as a lump or swelling in the neck, hoarseness, difficulty swallowing and shortness of breath.
2. Multiple Endocrine Neoplasia syndrome type 2 (MEN 2)
MEN 2 is a rare inherited condition that increases the risk of thyroid and other endocrine tumours. People with this syndrome must not use these medicines.
3. Known allergy to the active ingredient or any excipient
A serious hypersensitivity reaction to semaglutide, tirzepatide, liraglutide or other ingredients is a contraindication. Signs of allergy include swelling of the face, lips or throat, rash, itching, trouble breathing and fainting.
4. Pregnancy
Weight loss GLP-1 medicines are not recommended in pregnancy. If you plan to conceive, your prescriber will advise when to stop. Read more in our article on GLP-1 medicines, pregnancy and contraception.
5. Breastfeeding
There is not enough safety data, so these medicines are not recommended while breastfeeding.
Conditions Needing Caution or Specialist Advice
| Condition | Why caution is needed |
|---|---|
| History of pancreatitis | GLP-1 medicines have been associated with pancreatitis. Persistent severe abdominal pain needs urgent review. |
| Gallstones or gallbladder disease | Rapid weight loss and GLP-1 treatment increase the risk of gallstones and cholecystitis. See GLP-1 and the gallbladder. |
| Type 2 diabetes using insulin or sulfonylureas | Higher risk of low blood sugar. Doses of other medicines may need to be reduced. |
| Diabetic retinopathy | Rapid improvement in blood sugar may temporarily worsen retinal disease with semaglutide. |
| Kidney disease or dehydration risk | Vomiting and diarrhoea can cause acute kidney injury. |
| Severe gastrointestinal disease, including gastroparesis | These medicines slow stomach emptying and may worsen symptoms. |
| History of eating disorders | Appetite suppression can worsen disordered eating. |
| Depression or suicidal thoughts | Weight loss products carry a warning to monitor mood and behaviour. |
| Heart rate and heart disease | Heart rate can rise slightly. Your doctor will weigh benefits and risks. |
| Planned surgery or anaesthesia | Delayed stomach emptying may increase the risk of aspiration. Tell your care team. |
Who Should Not Take GLP-1 for Weight Loss Based on BMI or Age?
Prescribing criteria also exclude people who do not meet the clinical threshold. Weight loss indications generally apply to adults with a BMI of 30 or above, or 27 or above with at least one weight-related condition. Using these medicines for cosmetic weight loss in people with a normal BMI is not appropriate and carries risks without a clear benefit. Some products are approved for adolescents from 12 years, but treatment is specialist-led. Older adults need careful assessment because of frailty, muscle loss and dehydration risk. See our guides to eligibility for weight loss injections and who qualifies for prescription weight loss medication.
Medicines That Can Interact With GLP-1 Treatment
- Insulin and sulfonylureas. Higher risk of hypoglycaemia.
- Oral contraceptives with tirzepatide. May be less effective after starting and dose increases.
- Warfarin. Monitor INR more closely.
- Medicines with narrow therapeutic windows, such as levothyroxine, because absorption may change.
- Other GLP-1 products. Never combine two GLP-1 medicines.
Read GLP-1 drug interactions for more information.
Warning Signs to Stop and Seek Urgent Help
Seek urgent medical attention if you experience severe, persistent abdominal pain that may spread to the back, repeated vomiting, yellowing of the skin or eyes, signs of allergic reaction, a neck lump or trouble swallowing, vision changes, symptoms of severe low blood sugar such as confusion or fainting, or thoughts of self-harm. Do not wait for the next appointment. Our guides on Wegovy side effects and Mounjaro side effects list symptoms and management tips.
How a Prescriber Checks Your Suitability
The assessment usually includes your weight and height, medical history, family history, current medicines, allergies, pregnancy plans, mental health and lifestyle. Some prescribers request blood tests or examine blood pressure and heart rate. Be honest, because accurate information protects you. Our article on what to expect in an online weight loss consultation lists typical questions. Online services should follow the same rules; see the safe buying guide.
What If You Are Not Eligible?
Being told you cannot use a GLP-1 medicine is not the end of the road. Alternatives may include structured lifestyle programmes, dietitian support, other approved medicines such as orlistat or naltrexone-bupropion, treatment for underlying conditions, or referral to bariatric services. Our article on the Mysimba guide explains one non-GLP-1 option and the orlistat comparison explains another.
Never Use Unregulated Products to Get Around the Rules
If you are ineligible, buying pens from unregulated sellers to bypass the checks puts you at serious risk. Counterfeit pens have caused harm, and research-labelled compounds are not approved medicines. Read whether it is legal to buy research peptides and the compounded semaglutide guide for the risks.
For official safety information, see the FDA drug resources. If you have questions about your suitability, contact our team to start a clinician-reviewed assessment.
Understanding the Thyroid Warning: Who Should Not Take GLP-1 Because of Cancer Risk
The thyroid warning is the best-known reason people are told who should not take GLP-1 medicines. In rodent studies, semaglutide, liraglutide and tirzepatide caused thyroid C-cell tumours at exposures higher than those used in people. Rodent C-cells respond to GLP-1 differently from human thyroid tissue, and large human studies have not shown a clear increase in thyroid cancer. Even so, regulators require the boxed warning because medullary thyroid carcinoma is rare but serious, and the data cannot rule out a risk. If you have a first-degree relative with MTC or a known RET gene mutation, you should not use these products. Papillary thyroid cancer in the family is generally not the same as MTC, but you should still tell your prescriber so they can classify your risk correctly. Ask relatives what type of thyroid cancer they had if you are unsure.
Who Should Not Take GLP-1 If They Have Gastrointestinal Disease?
These medicines work partly by slowing gastric emptying. That helps with fullness but can worsen symptoms in people with diabetic gastroparesis, severe reflux, inflammatory bowel disease flares, bowel obstruction or a history of major stomach surgery. Reports of ileus (bowel paralysis) and aspiration during anaesthesia led to updated warnings. If you have persistent bloating, vomiting undigested food or early satiety before treatment, tell your prescriber. They may recommend investigations first or advise against treatment. Even in people without bowel disease, constipation can be severe in a minority, so know how to manage it with fibre, fluids and pharmacist-approved remedies.
Mental Health Considerations
Some weight management labels advise monitoring for depression, suicidal thoughts and unusual changes in mood or behaviour. Regulators in several regions have reviewed the evidence and not found a clear causal link with semaglutide, but caution remains sensible. If you have a history of severe depression, self-harm or an active eating disorder, a prescriber should discuss risks and support options. Contact your care team if you notice a significant change in mood, loss of interest, or thoughts of self-harm, and call emergency services in a crisis. Treating obesity can improve mental wellbeing for many people, but the effect is individual.
Special Populations: Children, Older Adults and Kidney or Liver Disease
Children under 12 should not use these medicines. Adolescents may be considered for some products under specialist care. Older adults may be more sensitive to dehydration and muscle loss, so doses are increased cautiously. People with mild to moderate kidney or liver disease may not need dose changes, but severe disease requires specialist input, and dehydration from vomiting is a risk for kidney function. People who have had weight loss surgery, have unstable heart conditions, or are undergoing cancer treatment need individual assessment. If you fall into one of these groups, ask your prescriber who should not take GLP-1 treatment in your situation, and make sure your specialist and your prescriber communicate.
Key Takeaways on Safety Screening
The big exclusions are personal or family medullary thyroid cancer, MEN 2, allergy to the ingredients, pregnancy and breastfeeding. Many other conditions need caution, including pancreatitis, gallbladder disease, severe gastrointestinal problems, diabetic eye disease, kidney problems and mental health concerns. Honest answers during your consultation are the best protection. If you are not eligible, ask about alternatives rather than seeking unregulated products.
Talking to Your Prescriber Honestly
Bring a list of diagnoses, surgeries, medicines and family cancers, and mention anything that worries you, from gut symptoms to mood. Honest answers let your prescriber decide who should not take GLP-1 treatment in practice, and make sure that you receive a plan that is safe, realistic and tailored to you.
Editorial Standards and Sources
This guide was prepared by the Weight Lose Solution clinical content team. Medicine information is checked against official product labels and published trial data, and we update articles when guidance changes. It is educational only: prescription treatments are dispensed after an online assessment and approval by a licensed physician, and your own prescriber always takes priority.
Key sources used across our guides:
- Wilding JPH et al. Once-weekly semaglutide in adults with overweight or obesity (STEP 1). New England Journal of Medicine, 2021.
- Jastreboff AM et al. Tirzepatide once weekly for the treatment of obesity (SURMOUNT-1). New England Journal of Medicine, 2022.
- U.S. Food and Drug Administration drug information and approved product labelling.
- World Health Organization obesity and overweight fact sheet.
Related Guides and Next Steps
Continue your research with these related guides from our clinical content team:
- Buying weight loss injections in the UK
- Buying weight loss injections in South America
- How to inject a weight loss pen step by step
- What to do after a missed dose
- Breaking a weight loss plateau on GLP-1
- How GLP-1 injections work
- Semaglutide vs tirzepatide
- Browse prescription weight loss medications
Frequently Asked Questions About Who should not take GLP-1
Who should not take Wegovy or Mounjaro?
People with a personal or family history of medullary thyroid carcinoma, those with MEN 2, anyone allergic to the ingredients, and people who are pregnant or breastfeeding should not use them.
Can I take GLP-1 medicines if I have had pancreatitis?
It requires caution and specialist judgement. Many prescribers avoid these medicines after pancreatitis, so discuss your history openly.
Are GLP-1 injections safe with diabetes?
They are approved for type 2 diabetes, but if you use insulin or sulfonylureas the risk of low blood sugar is higher and doses may need adjusting.
Can someone with a normal BMI use weight loss injections?
No. They are intended for adults with obesity or overweight with weight-related conditions. Using them for cosmetic weight loss is not appropriate.
Is it safe to take GLP-1 medicines with an eating disorder history?
Appetite suppression can worsen disordered eating, so your prescriber will assess risks and may recommend specialist support or alternative treatment.
What should I do if I develop severe abdominal pain on treatment?
Stop injecting and seek urgent medical care, because severe persistent abdominal pain can signal pancreatitis or gallbladder disease.
Medical disclaimer: this article is for general education and is not medical advice. Prescription treatments are dispensed only after an online health assessment and approval by a licensed physician. Always follow the guidance of your own prescriber and the patient information leaflet.