- Most side effects are gut-related and tend to ease over the first few weeks.
- Manage nausea with smaller portions, plainer food, eating slowly and stopping when full — not by changing your dose yourself.
- Severe, persistent tummy or back pain (especially with vomiting) can signal pancreatitis — seek urgent help.
- Sudden vision change: the MHRA now lists a very rare eye condition (NAION) as a side effect — sudden sight loss needs emergency eye care.
- Report side effects via the MHRA Yellow Card scheme, and speak to your pharmacist or GP if anything bothers you.
Which medicines this covers
Semaglutide is a GLP-1 receptor agonist. In the UK it is sold under three brand names, and the side-effect profile is broadly the same across them because they share the same active ingredient:
| Brand | Form | Licensed use in the UK |
|---|---|---|
| Wegovy | Weekly injection | Weight management (obesity) |
| Ozempic | Weekly injection | Type 2 diabetes |
| Rybelsus | Daily tablet | Type 2 diabetes |
For how these differ, how to access them and current UK supply, see our guide to Wegovy & Ozempic availability. You can follow official supply signals on our pages for semaglutide, Wegovy and Ozempic.
Common side effects
The NHS lists the common side effects of semaglutide as feeling sick (nausea) and being sick (vomiting), constipation, diarrhoea, feeling tired, itchy or red skin where you inject, and hair loss. These tend to be worst when you first start and shortly after each dose increase, and usually improve as your body gets used to the medicine.
If a common side effect bothers you or does not go away, the NHS advises speaking to your pharmacist or doctor — do not simply push through it or change your dose on your own.
Managing the common gut side effects
The gut symptoms are the main reason people struggle with semaglutide. General, non-medicine steps that many people find help include:
- Eat smaller portions and stop as soon as you feel full — the medicine slows stomach emptying, so large meals feel worse.
- Choose plainer, blander food when you feel sick, and go easy on rich, greasy, very sweet or spicy meals.
- Eat slowly and sit upright for a while after eating rather than lying down.
- Sip fluids through the day, especially if you have vomiting or diarrhoea, to avoid becoming dehydrated.
- For constipation, more fibre, fluids and gentle activity can help; ask your pharmacist before using any laxative.
- Avoid alcohol where you can — the NHS notes it can increase side effects like feeling or being sick.
Serious side effects and red flags
Some reactions are uncommon or rare but need prompt medical attention. Seek help from your GP, NHS 111, an eye casualty unit or A&E as appropriate if you notice:
| Warning sign | What it may mean | What to do |
|---|---|---|
| Severe, persistent pain in your stomach or back, often with vomiting | Inflamed pancreas (acute pancreatitis) | Get urgent medical help |
| Sudden change in eyesight — sudden sight loss, or vision that gets worse very quickly, in one or both eyes | May include NAION, a very rare eye nerve condition | Urgently attend eye casualty (if available) or A&E |
| Swollen throat or tongue, difficulty breathing, widespread rash | Serious allergic reaction (anaphylaxis) | Call 999 / emergency help |
| Shakiness, sweating, confusion, feeling very hungry (mainly if you also take insulin or a sulfonylurea) | Low blood sugar (hypoglycaemia) | Treat low sugar; speak to your diabetes team |
| Severe upper-tummy pain, feeling sick, sometimes with a high temperature or yellowing of the skin/eyes | Gallbladder problems (e.g. gallstones) | Get medical advice promptly |
In people with diabetes, rapid improvements in blood sugar can sometimes be linked to a temporary worsening of diabetic eye disease (retinopathy) — discuss eye monitoring with your diabetes team. If you are ever unsure whether a symptom is serious, call NHS 111, and call 999 for anything life-threatening such as difficulty breathing.
Pregnancy, contraception and breastfeeding
The NHS advises that semaglutide is not used during pregnancy, as there is not enough information to say it is safe for your baby. If you are planning a pregnancy, the guidance is to stop using semaglutide at least 2 months before you start trying to conceive, and to use contraception while you are taking it. If you think you might be pregnant, speak to your prescriber. This is a decision to make with your GP or specialist, not alone.
Reporting side effects
Report any suspected side effect — including vision changes — through the MHRA Yellow Card scheme. Reporting helps the MHRA monitor the safety of these medicines. For a plain-English overview of the medicine, see the NHS page on semaglutide, and always follow the patient information leaflet in your pack.
Related reading
Wegovy & Ozempic in the UK
The difference, access routes, shortages and safety essentials.
Mounjaro (tirzepatide) in the UK
Availability, price changes and the NHS rollout.
Does it cause muscle loss?
What the trials show about GLP-1 medicines and lean mass.
Orforglipron: the oral GLP-1
Where the once-daily tablet stands for UK availability.
Stay ahead of semaglutide supply changes
MediWatch checks official DHSC and NHS data daily and alerts you if your medication is affected.
Search shortages free →Official sources: NHS: semaglutide (side effects, pregnancy, alcohol) · MHRA Drug Safety Update: semaglutide and NAION (5 Feb 2026) · MHRA Yellow Card scheme
MediWatch is not medical advice. Always follow your prescription label and patient information leaflet, and ask a pharmacist, GP, specialist, NHS 111, or emergency services if you are unsure or unwell. Data checked daily against official sources.