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Who this guide applies to
This guide covers the shared practical issues that can arise with GLP-1 and related weight-management medicines, including semaglutide (Wegovy), liraglutide (Saxenda) and the dual GIP/GLP-1 medicine tirzepatide (Mounjaro).
These medicines are not identical. Doses, devices, missed-dose rules, storage instructions, interactions and some side effects differ. Follow the instructions for your own prescribed medicine and check its patient leaflet when the advice needs to be product-specific.
Quick answer
Nausea, diarrhoea, vomiting, stomach pain and constipation can happen with GLP-1 and related weight-management medicines. Stomach and bowel side effects are commonly more noticeable when first starting treatment and during dose increases. For many people they become less troublesome over time.
Not everyone gets side effects, and you do not need to put up with symptoms that are severe, persistent or getting worse.
Why can symptoms feel worse after a dose increase?
GLP-1 and related medicines use different dose schedules, but digestive side effects can become more noticeable when treatment starts or the dose is increased. This often improves as the body adjusts.
Do not copy a dose schedule from another medicine or another person. Only increase your dose according to the plan given by your own prescriber.
When during the week might symptoms feel worse?
Some patients report that side effects are more noticeable during the first three or four days after their weekly injection and ease as they approach the next dose. This is a patient-reported pattern, not a timetable that everyone will follow.
The timing varies between medicines and between people. Use the instructions for your own medicine rather than assuming that every weekly injection follows the same pattern.
If symptoms are mild and manageable
Side effects often improve as your body adjusts. Continue with simple supportive steps and give things time if you feel able—but this is not a test of endurance. Do not increase your dose yourself, and ask the clinical team for help if symptoms are troublesome, persistent or worsening.
- Take only the dose you have been prescribed.
- Choose smaller meals and stop when comfortably full.
- Drink regularly, particularly if you have vomiting or diarrhoea.
- Keep your prescribing team updated in the way they have asked.
- Ask for advice before the next planned review if symptoms are not settling.
Do not wait for a routine check-in
Seek urgent medical advice if you cannot keep fluids down, are passing very little urine, feel faint or very unwell, or have severe or persistent abdominal pain. Do not take another dose of your medicine and seek urgent medical help for severe persistent stomach pain, with or without nausea and vomiting, because this can be a sign of pancreatitis.
Read the fuller guide
See Managing side effects from GLP-1 and related medicines for a fuller symptom-by-symptom guide.
Official and clinical sources
MHRA: GLP-1 medicines—what you need to know
Guy’s and St Thomas’ NHS Foundation Trust: managing side effects with diet
First published July 2026. Scope and content reviewed 30 October 2026 against current MHRA, NHS and NICE guidance. Review earlier if product information changes.
Prepared for the Pathfields Healthy Living Portal.