Does Wegovy Cause Constipation — and What Can You Do About It?

What the STEP 1 trial actually found

The STEP 1 trial, published in the New England Journal of Medicine, enrolled 1,961 adults with obesity over 68 weeks and is the primary evidence base behind Wegovy's UK licence. Gastrointestinal events were the most common side effects across the board, and constipation sat alongside nausea, diarrhoea and vomiting in the list of frequently reported events. Around 24% of people taking semaglutide 2.4mg reported constipation, against roughly 11% of the placebo group, a meaningful gap that reflects the medicine's action on the gut, not coincidence.

The NHS semaglutide medicines page lists constipation as a common side effect, defining common as affecting between one in ten and one in hundred users. In practice, the trial figure is higher than that threshold suggests, which is worth bearing in mind when weighing up treatment. The SmPC and Patient Information Leaflet, available on the electronic Medicines Compendium, contain the full breakdown of frequencies by system, it is the document your prescriber uses when assessing your history.

The mechanism is straightforward. Semaglutide slows gastric emptying, which is partly how it produces the sustained feeling of fullness that drives weight loss. That same slowing extends downstream: transit through the large bowel takes longer, stool spends more time there, and water is absorbed from it, the textbook conditions for constipation. Dose increases tend to amplify this temporarily, which is why symptoms often peak in the first week or two after moving up the titration ladder.

When constipation on semaglutide is something to watch more carefully

Ordinary constipation during Wegovy treatment is uncomfortable but manageable. What matters is recognising the signs that something more serious is happening. If you develop severe, persistent abdominal pain (particularly pain that radiates to your back and comes with or without vomiting) seek medical help promptly. In January 2026, the MHRA issued a Drug Safety Update specifically addressing GLP-1 medicines and acute pancreatitis, noting it as an infrequent but potentially serious side effect that can present with abdominal pain. That is a different clinical picture from straining at the toilet, but the two can be confused.

Signs that warrant a call to your GP or, out of hours, NHS 111, include: abdominal pain that does not settle after a day or two, no bowel movement for more than a week despite trying standard measures, vomiting alongside constipation, blood in the stool, or any symptom that feels severe rather than just inconvenient. People who already have conditions affecting the bowel, such as irritable bowel syndrome, Crohn's disease or a history of bowel obstruction, should discuss this with a prescriber before starting treatment. Wegovy's UK licence and eligibility criteria are assessed individually precisely because medical history shapes the risk picture.

If you are unsure whether what you are experiencing counts as a side effect worth reporting, the MHRA's Yellow Card scheme is open to patients as well as clinicians at yellowcard.mhra.gov.uk. Reporting even mild, resolved side effects helps build the post-market safety picture for newer medicines like Wegovy, which still carries a Black Triangle (▼) status indicating active monitoring.

Practical steps most people find helpful

The good news is that most people can wegovy-related constipation can be eased with sensible changes. Hydration is often the first and most effective lever: the bowel needs water to move stool comfortably, and if nausea has led to reduced eating and drinking, dehydration compounds the problem quickly. Aim to sip water steadily through the day rather than drinking large amounts in one go, especially if nausea is also a factor.

Dietary fibre helps, though the timing matters. If nausea or a dramatically reduced appetite has cut your food intake significantly, overall fibre intake falls with it. Small, fibre-containing meals (vegetables, pulses, oats) are generally easier to manage than large ones during early treatment. Gentle physical activity, even a short daily walk, supports bowel motility in a way that sitting still does not.

Over-the-counter options such as bulk-forming laxatives or osmotic laxatives are commonly used alongside GLP-1 treatment, but the right choice depends on your full medical picture, which is why it is worth raising at your next clinical check-in rather than self-selecting from the pharmacy shelf without context. For more targeted practical advice, our page on how to treat constipation on Wegovy walks through the options in more detail. Some people also find it useful to read about strategies for stopping constipation on Wegovy before it becomes a problem, particularly before planned travel or around times like bank holidays when a pharmacy visit is harder.

The conversation to have with your prescriber

Constipation rarely needs to be endured quietly. A prescriber can consider whether the titration pace suits you, suggest specific interventions, or flag whether your symptoms warrant further investigation. At nume, every repeat order involves a clinical review (a real clinician reads your update, not an automated system) which is precisely when this kind of feedback matters. Withholding troublesome symptoms means the person overseeing your treatment cannot act on them.

If you are still weighing up treatment options and want to understand the broader profile of side effects before committing, our clinical team discusses suitability and what to expect as part of every free consultation. There is no pressure, no prescription automatically issued; it is an assessment of whether treatment is right for you and, if so, how to manage it safely. You can also read about other GI side effects such as burping on Wegovy, which some people experience alongside constipation, especially in the early weeks.

For a broader view of what to expect from semaglutide as a treatment, the cost and what it includes page covers the service structure, while our about us page sets out the clinical oversight behind everything we do.