Side effect guide
Find your symptom. Each card says what helps at home, how long to expect and the signs which mean you need help the same day.
Usually mildNausea
What helps. Most common in the week after a dose or a step up. Eat small, bland meals, stop eating when you feel full, and avoid fatty or sugary food. Ginger or peppermint tea helps some people. Nausea usually eases within two to three weeks.
Get help the same day if: Vomiting for more than 24 hours, or being unable to keep fluids down.
Watch closelyVomiting
What helps. Occasional vomiting after a dose is common. Sip fluids often, rest, and return to small meals once settled. Tell your clinical team at your next check-in.
Get help the same day if: Vomiting for more than 24 hours, blood in vomit, or signs of dehydration such as dark urine and dizziness.
Usually mildConstipation
What helps. Food moves more slowly on GLP-1 treatment. Drink 2 litres of fluid a day, add fibre gradually, walk daily, and ask your pharmacy team about a gentle laxative if nothing passes for three days.
Get help the same day if: No bowel movement for a week with stomach swelling or pain.
Usually mildDiarrhoea
What helps. Usually short lived after a step up. Drink extra fluid, eat plain food, and avoid alcohol, caffeine and artificial sweeteners until your gut settles.
Get help the same day if: Diarrhoea for more than 48 hours, or with fever or blood.
Usually mildHeartburn or reflux
What helps. Eat earlier in the evening, avoid lying down for two hours after meals, and raise the head of your bed. Over-the-counter antacids are safe to use alongside treatment.
Get help the same day if: Pain or difficulty swallowing, or black stools.
Watch closelyStomach pain
What helps. Mild cramping after meals is common. Severe pain which spreads to your back, does not ease, and comes with vomiting can be pancreatitis, which is rare but serious.
Get help the same day if: Severe stomach pain which does not ease, especially with vomiting or fever. Call 999 or go to A&E.
Usually mildTiredness
What helps. Common in the first weeks as you eat less. Keep protein up, drink enough, and keep moving gently. Tiredness usually passes as your body adjusts.
Get help the same day if: Extreme weakness, confusion or fainting.
Watch closelyDizziness
What helps. Often linked to eating or drinking too little. Have regular small meals and fluids. If you take blood pressure medicine, your dose may need review as you lose weight.
Get help the same day if: Fainting, or dizziness with a racing heart or chest pain.
Usually mildHeadache
What helps. Usually from dehydration or low food intake. Drink more fluid, do not skip meals, and use paracetamol if needed.
Get help the same day if: A sudden severe headache, or one with vision changes, stiff neck or confusion.
Usually mildInjection site reaction
What helps. Redness, itching or a small lump at the site is common and fades within days. Rotate sites each week and let the pen reach room temperature before injecting.
Get help the same day if: Spreading redness, heat, pus or fever.
Usually mildHair shedding
What helps. Linked to rapid weight loss rather than the medicine. Shedding usually starts around month three and regrows within six months. Keep protein at 1.2 to 1.6 g per kg of body weight.
Get help the same day if: Patchy bald areas or shedding with a rash, which need a GP review.
Watch closelyShakiness or sweating
What helps. GLP-1 treatment alone rarely causes low blood sugar. The risk rises if you also take insulin or a sulfonylurea. Eat something with carbohydrate and tell your prescriber.
Get help the same day if: Confusion, seizure or loss of consciousness. Call 999.
Can be urgentPain under the right ribs
What helps. Rapid weight loss raises the risk of gallstones. Pain under the right ribs after fatty meals, with nausea, needs a same-day GP review.
Get help the same day if: Severe pain with fever, yellowing of the skin or eyes, or dark urine. Call 999 or go to A&E.
Can be urgentRash, swelling or wheeze
What helps. A mild rash can be watched. Swelling of the face, lips or throat, or trouble breathing, is an emergency.
Get help the same day if: Any swelling of the face, lips or throat, or difficulty breathing. Call 999.
Watch closelyLow mood
What helps. Changes in appetite and routine can affect mood. Tell your clinical team at any time. Treatment can be paused or stopped.
Get help the same day if: Thoughts of harming yourself. Call 999, go to A&E, or call Samaritans on 116 123.
Questions about this tool
Is this medical advice?
This page gives general information about common side effects of GLP-1 weight loss medicines. Contact your own prescriber or pharmacist for advice about symptoms. Do not wait for an online reply if you need urgent help.
How long do side effects last?
The duration depends on the medicine, symptom and individual. Gastrointestinal symptoms can occur during dose escalation, but do not assume that persistent or worsening problems are harmless. Ask your prescriber or pharmacist for advice and follow the leaflet’s urgent warning instructions.
Should I stop treatment if I feel unwell?
Seek advice according to the severity of your symptoms. Call 999 for a life-threatening emergency; use NHS 111 for urgent advice when needed. For other concerns, contact your prescriber or pharmacist before deciding what to do about the next dose.
How do I report a side effect?
Tell your prescriber or pharmacist about suspected side effects. You can also report them through the MHRA Yellow Card scheme, including the medicine and what happened. Reporting helps monitor safety but does not replace medical advice or urgent care.
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Page information
- Summary
- Fifteen common symptoms on Mounjaro, Wegovy and the GLP-1 tablets, each with what helps at home and the signs which need same-day or emergency care.
- Publisher
- Aero Clinic, operated by AERO HEALTHCARE LTD.
- Editorial update
- Clinical review
- Pending. An editorial update is not a clinical sign-off.
Cite as: Side effect guide, Aero Clinic (https://www.cagri.co.uk), AERO HEALTHCARE LTD. https://www.cagri.co.uk/symptom-guide. Editorial update: 4 November 2026. Clinical review pending.