Why Do I Have Diarrhoea on Wegovy — and How Long Does It Last?

Why semaglutide slows your gut and what that means day-to-day

Semaglutide works by activating GLP-1 receptors in the brain and gut, which reduces appetite and slows the rate at which food leaves the stomach. That change in gut motility is the mechanism behind most of Wegovy's gastrointestinal side effects. Slower gastric emptying is actually central to how the medicine produces its effect, but the bowel doesn't always respond uniformly, some people experience constipation, others loose stools or diarrhoea, and some move between the two during the titration period.

The NHS semaglutide medicines page lists diarrhoea as a very common side effect, meaning it affects more than 1 in 10 users. If you are curious about the biology behind that figure, our page on why you get diarrhoea on Wegovy explains what is happening in the gut in plain terms. The pattern most people describe is loose stools that are worst on the day of or the day after an injection, particularly during the first month or after moving to a higher dose. For many, it has largely settled before the next dose increase is due.

Practical steps that consistently help: eating smaller portions (which Wegovy itself tends to nudge you towards), avoiding very fatty or heavily spiced food during a flare, and keeping fluid intake steady throughout the day rather than drinking large amounts at once. Keeping a brief note of when symptoms peak can be useful to share with your prescriber at review. For a fuller picture of the broader side-effect profile, the Wegovy side effects overview covers the complete range.

Dose increases: the riskiest moments for your stomach

Diarrhoea (along with nausea and stomach cramps) is reliably more likely in the first two to four weeks at each new dose level. The titration schedule for Wegovy is deliberately gradual, starting at 0.25mg and stepping up roughly every four weeks, specifically to allow the gut to acclimatise. Even so, some people find certain steps harder than others; the jump from 1.7mg to 2.4mg is the one prescribers hear about most often.

If a particular dose increase brings persistent loose stools that are disrupting daily life, that is worth raising with your prescriber. In some cases, staying at a lower dose for an additional month is the right clinical call, a decision the prescriber makes based on your individual picture, not something to adjust unilaterally. The mechanism behind Wegovy-related diarrhoea and the evidence on semaglutide and loose stools are explored in more detail on those pages if you want the deeper background.

One practical point worth flagging: if you take your injection on a Friday evening, the peak gut-reaction window often lands on the weekend. Several people on treatment find that suits them, any rough morning means they are not caught out at work or on the school run. Others do the opposite and choose a weekday so they can contact their prescriber promptly if something feels off. There is no medically superior day; choose what fits your week.

When to get medical help, and how to report side effects

Most diarrhoea on Wegovy is unpleasant but not dangerous. There are, however, specific situations where you should act quickly. The NHS England guidance on weight management injections is clear that severe or persistent GI symptoms warrant prompt clinical review, particularly because significant fluid loss can affect kidney function.

Seek medical help promptly if you experience any of the following: diarrhoea that has lasted more than a few days without any improvement; signs of dehydration such as dizziness, a dry mouth or very dark urine; inability to keep fluids down; severe abdominal pain, especially any that radiates to the back (which can signal pancreatitis, a rare but serious side effect of GLP-1 medicines that the MHRA highlighted in a 2026 Drug Safety Update). If symptoms are sudden and severe, NHS 111 or your GP are the right first contacts. Do not simply stop the medicine without advice, as that is itself a clinical decision.

You can also report any suspected side effect directly to the MHRA through the Yellow Card scheme. Reporting is open to patients as well as healthcare professionals, and it is one of the ways regulators track how medicines perform in the real world beyond trial conditions. If you want to review what else can occur during treatment, the full list of possible Wegovy side effects covers every category with the same level of balance.

Talking to a prescriber, before and during treatment

Side-effect discussions are a normal, central part of any responsible prescribing process. At nume, a GPhC-registered Independent Prescriber reads every consultation personally (not a software triage system) on the same day the form is submitted. That review covers your health history, any medicines you already take, and whether semaglutide is the right fit, including how you might be likely to tolerate the GI effects given your individual picture.

If you are already on Wegovy and struggling with diarrhoea, the aftercare team is available seven days a week. If you are still weighing up whether the treatment is right for you, more background on how Wegovy works and the broader context of weight-loss treatment options may help before you decide. Prescription weight-loss medicines are reviewed against your full picture; a prescriber is always the right person to judge whether, and at what pace, treatment should continue. Check your eligibility with our clinical team, the consultation is free, and it is where side-effect questions like this one are properly answered.