WEIGHT LOSS GUIDE
Side effects: what's normal and when to seek help
Understand what to expect as your body adjusts, how to manage common effects, and the warning signs that need urgent attention.
Understanding side effects
When you start a GLP-1 medicine, it’s natural to pay close attention to how you feel — and to notice things you’d usually ignore. That heightened awareness usually settles over the first few weeks. Side effects can also vary week to week as your body adjusts; that fluctuation is normal and doesn’t mean the medicine is being tolerated less well.
And you don’t need to feel unwell for treatment to be working. Some people have a bumpier start; others barely notice anything. Both are normal responses to the same medicine.
Common effects and how to manage them
Because the medicine slows stomach emptying, food stays longer and can trigger queasiness. It helps to drink plenty of fluids, get fresh air, eat small frequent meals, and cut back on sugary or fatty foods and strong smells.
Sip water and try ginger or peppermint tea; stick to bland foods like toast, rice and bananas. Contact your GP or 111 if it lasts more than a couple of days, you show signs of dehydration, or you use oral contraception and vomited within 3 hours of your pill.
Stay hydrated, eat small frequent meals, and consider oral rehydration salts. Contact your GP or 111 if it lasts over a week, there’s blood, you’re dehydrated, or you use oral contraception and it has lasted over 24 hours.
Drink plenty of fluids, eat high-fibre foods (prunes, figs, oats), and stay active. See your GP if it doesn’t improve or you notice blood.
Often linked to dehydration. Drink fluids, use simple pain relief like paracetamol, and get enough sleep. Contact your GP or 111 if it lasts more than a few days, worsens, or comes with vision changes.
Often it’s the sudden drop in how much you’re eating rather than the medicine itself. Make sure you’re eating enough nutrient-dense food with enough protein, and keep a regular sleep routine.
Mild redness, itching, a small lump or bruise are common and harmless. Rotate your injection site each week. See your GP if you notice spreading redness, warmth, pus, or a fever.
Tingling or pins-and-needles, reported more often at the Wegovy 7.2 mg dose. It’s not nerve damage and usually settles. Avoid tight clothing and friction, moisturise, and stay hydrated. Seek advice if it persists or disrupts daily life.
Usually caused by rapid weight loss rather than the medicine directly, and typically temporary. Aim for gradual loss (0.5–1 kg/week) and ensure enough protein, iron and B vitamins.
More likely if you have type 2 diabetes and take other glucose-lowering medicines. Treat symptoms promptly with something sugary, then a longer-lasting snack. Speak to your GP if episodes are frequent.
Serious effects to watch for
Pancreatitis — severe, persistent stomach pain (often radiating to the back), especially with repeated vomiting, needs urgent attention. Serious allergic reaction — difficulty breathing or swelling of the lips, tongue or throat is a medical emergency. Gallbladder problems — severe pain under the right ribs, sometimes with vomiting, fever or a rapid heartbeat.
When to seek urgent help
- Severe or persistent stomach pain, or vomiting blood or something like coffee granules
- Difficulty breathing, or swelling of the lips, tongue or throat
- Severe pain under the right ribs spreading to the shoulder or back, with vomiting or fever
- Sudden weakness, facial drooping, trouble speaking or vision changes
Contact your GP or NHS 111, or in an emergency call 999.
A note on other medicines and conditions
Many people on GLP-1 treatment also take other medicines or manage existing conditions, and for most this is completely safe. Your prescriber reviews your history before prescribing. If anything changes — you start or stop a medicine, or your health changes — let the clinical team know so treatment stays safe.
Ready to start?
Complete a short online consultation and a prescriber will check whether treatment is right for you.
This guide is general information and does not replace the advice of your prescriber or the patient information leaflet supplied with your medicine. If you feel unwell or have urgent concerns, contact your GP, NHS 111, or in an emergency call 999.
