Problems With GLP-1 Medicines: What to Expect (October 2026)

01 · The core answer

Are the problems with GLP-1 medicines relevant to you?

For most people the problems are manageable and short-lived, but they are real and worth planning for. Like all medicines, Mounjaro can cause side effects, and most are digestive.¹ The most common — affecting more than 1 in 10 people — are nausea, diarrhoea, vomiting, constipation and abdominal discomfort.¹³

Common effects (up to 1 in 10) include indigestion, reduced appetite, dizziness, reflux, burping, hair shedding and injection-site reactions.¹

02 · Your next step

What to do next

If you are considering treatment, the sensible step is a prescriber review of your history, medicines and expectations. Our weight loss clinic explains how that works. The consultation is free and reviewed by a GPhC-registered prescriber.

Related guides: Agonisti glp 1 and Ampk and glp-1 and Trapezoid glp 1 and Wat is glp-1.

Related guide: Mounjaro problems.

03 · Stomach problems

GLP-1 stomach problems and how to ease them

Stomach problems come from the medicine's main action: it slows how quickly the stomach empties.¹ Nausea, vomiting and diarrhoea were more common while the dose was being increased and became less frequent over time.¹

Practical steps help most people: eat smaller meals slowly, stop at the first feeling of fullness, favour plain lower-fat foods while adjusting, stay well hydrated, and avoid lying down straight after eating.¹³ If nausea or vomiting is persistent or you cannot keep fluids down, contact your clinical team — dehydration needs prompt attention.

Constipation is the other regular complaint. Fluids come first, then fibre from vegetables and whole grains, and daily movement. A pharmacist can recommend a suitable laxative if it persists, and you should contact your clinical team for pain, bloating or several days without a bowel movement.¹³

04 · Serious side effects

Serious problems: when to seek help

Serious side effects are uncommon but need urgent attention.¹³ Seek immediate medical help for severe, persistent stomach pain that may spread to your back, with or without vomiting, which could be pancreatitis.¹³

Pain in the upper right abdomen, fever or yellowing of the skin or eyes could be a gallbladder problem — get medical help straight away. Swelling of the face or throat and difficulty breathing are signs of a severe allergic reaction — get medical help straight away.¹³

If you take insulin or a sulfonylurea alongside Mounjaro, watch for low blood sugar, such as shakiness, sweating or confusion. Your prescriber may need to adjust those medicines.¹³ You can report any suspected side effect through the Yellow Card scheme.¹⁹ If you take the contraceptive pill, Mounjaro slows stomach emptying, which can reduce how well it is absorbed. Switch to a non-oral method, or add a barrier method such as condoms, for 4 weeks after starting Mounjaro and for 4 weeks after each dose increase. Mounjaro must not be used during pregnancy, and it should be stopped at least one month before trying to conceive.

05 · Hair, face and skin

Hair shedding, tiredness and "Ozempic face"

Hair loss was reported by 4.9% of people taking tirzepatide in the weight-management trials, compared with 1.0% on placebo.¹ It is linked to rapid weight loss itself rather than a direct drug effect, and for most people it settles as weight stabilises.

Fatigue is most noticeable in the first weeks and after dose increases. It usually reflects the body adjusting and simply eating less, so keep meals balanced, with enough protein, and stay hydrated. Tell your clinical team if tiredness is severe or not settling.

"Ozempic face" is not a drug effect. It is what losing a significant amount of weight quickly can do to facial volume, on any method including diet or surgery. The same applies to loose skin. Protecting lean mass with adequate protein, resistance exercise and a pace guided by your prescriber helps.

06 · Injection and mood

Injection-site reactions and mood

Injection-site reactions were reported by 8.0% of people taking tirzepatide in the weight-management trials, compared with 1.8% on placebo.¹ Mild redness, itching or a small bruise normally settles within a few days. Rotating sites each week helps, and contact your clinical team if a reaction is spreading, hot, very painful, or lasts more than a week.

On mood, the EMA's safety committee reviewed the evidence and concluded in 2024 that it does not support a causal link between GLP-1 medicines and suicidal thoughts, and the MHRA keeps this under continuous review.¹⁷ Even so, big changes in weight, appetite and routine can affect how you feel. Tell your prescriber about any history of depression, and seek help promptly if your mood drops or you have distressing thoughts during treatment.

If you have thoughts of harming yourself or ending your life, get help straight away. Call 999 or go to A&E if you are in immediate danger. In England you can call NHS 111 and choose the mental health option, any time. You can also call Samaritans free on 116 123, day or night. Tell your prescriber about any change in your mood while taking Mounjaro.

07 · Stopping and timing

Why some people stop treatment

Most side effects appear in the first days after starting or increasing a dose, peak early and settle. That is why Mounjaro uses a gradual dose ladder, and if a new dose is hard to tolerate, prescribers can hold the current dose longer before stepping up.¹

In the weight-management trials, 1.9% of people on 5mg, 3.3% on 10mg and 4.3% on 15mg stopped treatment permanently because of gastrointestinal side effects, compared with 0.5% on placebo.¹ Speak to your clinical team rather than pushing through severe symptoms.