Semaglutide Risks: What to Expect, What to Watch For

Step 1, The first few weeks: the GI risks most people actually experience

Start here, because this is where semaglutide's risk profile is most visible. The dose schedule begins low (0.25 mg, moving up roughly every four weeks) specifically to reduce the likelihood of severe gastrointestinal symptoms. Even so, nausea is common. Vomiting, loose stools, constipation, indigestion, reflux and persistent burping can all occur. If you've been wondering about that unpleasant sulphurous sensation, the sulfur burp experience on Wegovy is worth reading separately.

For most people these effects are self-limiting. They are most noticeable in the days following an injection, particularly after moving to a higher dose. Eating smaller portions, staying well hydrated, and avoiding fatty or very rich foods helps. The NHS medicines guidance on semaglutide (the NHS semaglutide page) describes the full side-effect list along with practical management advice.

There is one practical risk buried inside the GI picture that is easy to overlook: if vomiting or diarrhoea is prolonged, dehydration becomes a real concern, and dehydration puts stress on the kidneys. Drinking enough fluid is not just comfort advice. It is part of managing this medicine safely.

Step 2, Ongoing risks that don't always announce themselves clearly

Gallbladder problems sit in the middle tier of semaglutide risks: more serious than everyday nausea, less common than GI upset, and easy to dismiss at first because symptoms can be vague. Gallstones and gallbladder inflammation have been reported in clinical trials and in post-marketing surveillance. Upper right abdominal pain, particularly after eating, is worth mentioning to a doctor, not panicking about, but not ignoring either.

Pancreatitis deserves its own mention. In January 2026, the MHRA issued a Drug Safety Update specifically about GLP-1 medicines and acute pancreatitis, confirming it as a known but infrequent risk requiring vigilance. The warning sign is severe, persistent stomach pain that radiates into the back, sometimes accompanied by vomiting. This is not the ordinary nausea of dose adjustment; it is different in character and intensity. Anyone experiencing it should stop the injection and seek urgent medical attention. The full breakdown of Wegovy risks and side effects covers the pancreatitis picture in more detail.

There are also interactions worth knowing about before you start. Women using oral contraceptives should add a non-oral method of contraception for the first four weeks of tirzepatide treatment, and for four weeks after each dose increase; NHS guidance notes the evidence base for this interaction is stronger for tirzepatide than for semaglutide, but it is worth raising at consultation. Anyone taking oral medications with narrow timing requirements should discuss absorption timing with their prescriber, since semaglutide slows gastric emptying.

Step 3, When to get medical help without waiting

Most side effects can be managed with a call or message to your prescriber. Some cannot wait. Seek urgent medical help if you experience any of the following.

Severe, persistent abdominal pain reaching into your back, with or without vomiting: possible pancreatitis. A serious allergic reaction, swelling of the face, lips or throat, difficulty breathing, a widespread rash: stop the injection and call 999 or attend A&E. Signs of severe dehydration after prolonged vomiting or diarrhoea: rapid heartbeat, very little urine, extreme dizziness. Sudden changes in vision if you have a history of diabetic retinopathy. Low mood, thoughts of self-harm or suicidal thoughts: call your GP, 111 or the Samaritans (116 123) immediately.

If you are having surgery (planned or emergency) tell your anaesthetist and surgical team that you take semaglutide. Delayed gastric emptying affects anaesthetic safety. NHS England's guidance on weight-management injections covers this explicitly, and it is not a warning to skip. The semaglutide risks and benefits page puts the full picture alongside the clinical evidence for weight reduction, for anyone weighing the decision.

Step 4, Reporting and what happens next

Semaglutide still carries a Black Triangle (▼) designation in the UK, meaning the MHRA actively wants reports of suspected side effects, including ones that seem minor. Yellow Card reporting at yellowcard.mhra.gov.uk takes about ten minutes and directly informs the ongoing safety picture for this medicine. It is worth doing.

If a side effect is affecting your daily life, a prescriber can often adjust the dose or timing rather than stopping treatment entirely. That conversation matters. At nume, our prescribers discuss suitability and side effects as part of every consultation, if you want to start that conversation, it is free and takes place the same working day. You can also read more about how the Wegovy side effects profile compares across doses, or explore the risks of taking semaglutide from a broader clinical angle. Anyone who has questions about what is included in our service can find the detail on the about us page.