Semaglutide and infection risk: what the evidence actually shows

You notice something feels off a few weeks in, here's what the data says

Picture this: you're three or four weeks into Wegovy and you start getting that familiar burning sensation when you urinate. Your first instinct might be to wonder whether the injection is somehow to blame. According to trial data, you wouldn't be alone in asking. UTIs were reported in a subset of participants across semaglutide studies, and the NHS medicines page for semaglutide lists urinary tract infections among side effects that some people notice. The signal is real, but context matters: the absolute numbers were small, and UTIs are common in the general population regardless of any medicine. If you'd like the fuller picture on the UTI connection specifically, our semaglutide and UTI page goes through the trial figures in more detail.

A question our prescribers hear most weeks is whether having a history of recurrent UTIs should rule someone out from starting semaglutide. It doesn't automatically, but it is exactly the kind of thing a prescriber needs to know about at the consultation stage, so it can be factored into the overall assessment. Telling your prescriber upfront is always the right move.

The yeast infection link, and why blood sugar plays a part

Yeast infections, particularly vaginal candidiasis, have also appeared in post-marketing reports for GLP-1 medicines including semaglutide, a GLP-1 receptor agonist that has become one of the most widely discussed weight-loss medicines in recent years. The mechanism here is indirect. Semaglutide lowers blood-glucose levels in people whose insulin response was previously impaired, and in the short term, while glucose is still fluctuating, conditions can favour the overgrowth of Candida. The gut-slowing effect of GLP-1 medicines may also subtly alter the environment for gut bacteria, though the evidence on this is less settled. If you want to understand the proposed biology in more detail, our page on why semaglutide can cause yeast infections covers it step by step.

For most people this resolves as the body adjusts. Standard treatments (topical antifungals, for example) continue to work normally alongside semaglutide. If you're getting recurrent episodes, though, that is worth a conversation with your GP, not a dose adjustment made on your own. You can read more about how semaglutide works in the body to understand why these effects cluster around the first weeks of treatment.

What semaglutide does not appear to do to your immune system

It's worth being clear about what the evidence does not show. There's no established signal in the clinical trial data that semaglutide broadly suppresses immune function or raises the risk of serious bacterial infections, respiratory infections or anything in that category. The STEP 1 trial (68 weeks, 1,961 adults with obesity) did not flag immune suppression as a concern, and the NICE appraisal of semaglutide for weight management (TA875) does not list immune compromise among the medicine's risks. The specific infection signals that do appear are localised and plausible given the medicine's mechanism, rather than being a sign of global immune weakening.

People sometimes conflate Wegovy with immunosuppressants, medicines that deliberately dial down the immune response. Semaglutide is not in that category. It acts on GLP-1 receptors involved in appetite and blood-sugar regulation. You can find a broader overview of the medicine on our Wegovy page.

When to get medical help, and what not to sit on

Most infections that arise during semaglutide treatment are straightforward and respond to standard care. But a few situations need prompt medical attention. Seek help the same day if you have: a UTI that isn't improving after 48 hours of treatment, a temperature above 38°C alongside other symptoms, or signs of a kidney infection (loin pain, rigors, vomiting). Severe stomach pain that radiates towards the back is a separate concern, the MHRA issued a Drug Safety Update on acute pancreatitis in people taking GLP-1 medicines, and that symptom pattern warrants emergency assessment, not a wait-and-see approach.

If you're unsure whether what you're experiencing is a known side effect or something to flag urgently, the MHRA's Yellow Card scheme lets you report suspected reactions, and our aftercare team is available seven days a week. Wegovy is a prescription-only medicine; dose decisions and any changes to treatment because of an infection should always go through a clinician. If you have questions about cost or what's included in a private consultation, our Wegovy pricing page sets that out clearly. For anyone thinking about starting, our weight-loss overview explains who the available treatments are designed for.