The Complications of Wegovy Worth Knowing Before You Start

The complications you'll almost certainly encounter — and why they usually settle

Ask anyone who has been on Wegovy for six months, and they'll tell you the first few weeks are the roughest. Nausea is the most commonly reported effect, followed by loose stools, constipation (which some people find surprises them after hearing the nausea stories), indigestion, reflux, and burping. Fatigue and mild headaches appear too, particularly after starting or stepping up to the next dose in the schedule.

These effects are directly linked to how semaglutide works: slowing gastric emptying means food stays in the stomach longer, which presses on receptors that signal fullness, and nausea. The discomfort is real, but for the majority of people on the dose schedule set out in the Wegovy SmPC, it improves meaningfully within days to two weeks. The Wegovy treatment page has context on the titration process, which is specifically designed to keep these effects manageable by starting low.

Injection-site reactions (redness, mild swelling, a small itch) are also common and almost always trivial, particularly if you rotate injection sites correctly. The technique matters more than most people realise at the start; the guide to Wegovy injection technique walks through the practicalities that reduce site reactions. One misconception worth gently setting aside: some people assume the side effects get steadily worse with each dose increase. In practice, they tend to peak briefly after a new dose and then fall back, rather than accumulating over time.

Rarer but serious: the complications that need quick action

There is a group of complications that are uncommon but not negligible, and the right response to them is medical help, not waiting to see if they pass. Acute pancreatitis sits at the top of that list. In January 2026, the MHRA's Drug Safety Update for GLP-1 medicines drew attention to pancreatitis as a known risk: the signal to act is severe, persistent abdominal pain that radiates toward the back, with or without vomiting. Go to A&E or call 999 if that happens, do not manage it at home.

Gallbladder problems, including gallstones and gallbladder inflammation, are another recognised complication, particularly with rapid weight loss. Sharp pain under the right ribcage, especially after eating, deserves assessment. Dehydration from severe or prolonged vomiting and diarrhoea can strain the kidneys; staying hydrated during a GI episode matters, and if you cannot keep fluids down you need clinical input.

Allergic reactions (rash, swelling around the mouth or throat, difficulty breathing) are rare but serious; stop the injection and seek emergency help. For people with a history of diabetic retinopathy, a rapid change in blood glucose levels can worsen eye symptoms; this is worth discussing with a prescriber before starting. Contact details for the nume clinical team are on the contact page if you have questions between consultations.

Who faces a higher baseline risk, and why clinical assessment exists

Not every complication risk is equal across patients. Your personal and family health history shapes how the risk profile looks for you specifically. A personal or family history of medullary thyroid carcinoma, or of multiple endocrine neoplasia type 2 (MEN2), makes Wegovy unsuitable under its licensed terms. A history of pancreatitis, certain inflammatory bowel conditions, or gastroparesis requires careful prescriber consideration.

The full semaglutide indications page covers the licensed criteria in detail. Beyond absolute contraindications, there are interactions with other medicines that can alter how complications present; the Wegovy medication interactions guide is worth reading if you take other regular medicines, including oral contraceptives, where absorption timing matters with a GLP-1.

This is precisely what clinical assessment is for. At nume, a GPhC-registered Independent Prescriber reads your consultation personally (your health history, current medicines, and relevant background) before any prescription is issued. Every repeat order goes through the same review. The cost of that safety infrastructure is part of what you pay for; the treatment overview page sets out what's included at one transparent price.

When to get medical help, and the Yellow Card route if something unexpected happens

Being clear-eyed about warning signs makes treatment safer. Seek urgent help for: severe or persistent abdominal pain (especially pain radiating to the back); signs of a serious allergic reaction; inability to keep fluids down for more than 24 hours; significant worsening of mood or any thoughts of self-harm. Less urgent but worth a prescriber call: prolonged constipation, unexplained vision changes, or any new symptom that doesn't fit the typical GI pattern and doesn't resolve.

The MHRA's Yellow Card scheme lets patients report suspected side effects directly to the regulator, something the NHS actively encourages, because Wegovy still carries a Black Triangle (▼) status requiring additional monitoring. You do not need a GP to submit a Yellow Card report; you can do it yourself online. If you are new to treatment and wondering where to start the whole process, the guide to obtaining Wegovy safely in the UK explains the legitimate prescription route and what to watch for from unverified sellers. For a clinical conversation about your specific situation, you can start your free consultation with nume at any point.