Mounjaro and nasal congestion: should you be concerned?

How common is nasal congestion with tirzepatide, and why does it happen?

The honest answer is: uncommon, but real. In the SURMOUNT-1 trial, which randomised over 2,500 adults with obesity to tirzepatide or placebo over 72 weeks, upper respiratory tract symptoms including nasal congestion were captured in adverse-event reporting. The frequency sits in the 'infrequent' bracket, meaning it showed up in fewer than one in a hundred participants. That's a small figure, but if you're the one person in a hundred, it still needs answering.

The mechanism isn't fully pinned down, but it's plausible. GIP and GLP-1 receptors (both activated by tirzepatide) have been identified in respiratory tissue, and changes in how those receptors are stimulated may trigger mild local inflammation. Gastric slowing, another tirzepatide effect, can occasionally encourage post-nasal drip as a downstream result. Some people also experience a mild immune-like response as the body adjusts to a new medicine, which can manifest as congestion. For a more detailed look at how tirzepatide interacts with digestion and the gut, the overview of how Mounjaro affects digestion covers that territory.

The NHS tirzepatide medicines page lists nasal and sinus symptoms among less common side effects and advises telling your pharmacist or doctor if they bother you or don't settle.

Timing matters: when nasal symptoms are most likely to appear

Many people who notice a blocked or runny nose on Mounjaro report it in the first week or two after starting, or after a dose step-up. That timing is important. The body's adjustment period after a dose increase is when most tolerability side effects (nausea, fatigue, GI discomfort) are also at their peak. Nasal symptoms that arrive alongside those and then fade as the dose settles are probably part of the same picture.

If your congestion appears weeks into a stable dose and there's no dose change to explain it, the cause is more likely seasonal, environmental, or a separate respiratory infection. UK winters being what they are, a blocked nose in January is rarely a pharmacological event. Keeping a rough note of when symptoms started relative to your most recent pen helps your prescriber make that distinction quickly. Your prescriber may have asked you about timing as part of your initial clinical questionnaire.

One practical thing worth knowing: your Mounjaro pen lives in the fridge, so if you're feeling under the weather, it's easy to conflate mild cold symptoms with a treatment side effect. Separating the two (timing, whether others around you are ill, whether you have a temperature) gives you a cleaner picture to relay.

When to raise it with your prescriber or a doctor

Mild congestion that comes and goes is low priority in the side-effect hierarchy for a medicine like tirzepatide. It doesn't require stopping treatment, and there's no MHRA Drug Safety Update specifically addressing nasal symptoms with GLP-1 medicines (as opposed to the January 2026 update on pancreatitis, which covers a different concern). But there are times when you should not simply wait and see.

Contact your prescriber or GP promptly if: congestion is accompanied by significant facial pain or pressure around the sinuses; you develop a high fever alongside nasal symptoms; symptoms are getting worse rather than settling; or you have a history of chronic sinusitis and your usual pattern is changing. These features point toward sinusitis or another condition that needs its own treatment, independent of your Mounjaro use. Do not adjust your dose or timing because of nasal symptoms without speaking to your prescriber first. If you're unsure whether your experience is typical or needs attention, our Mounjaro questions and answers page covers a range of situations like this where knowing when to act is the key judgement call.

The MHRA Yellow Card scheme lets you report any suspected side effect directly to the regulator, it genuinely helps build the evidence base for medicines like tirzepatide, which carries a Black Triangle (▼) status indicating it is under enhanced monitoring.

The bigger context: nasal symptoms versus the side effects that actually need attention

Putting nasal congestion in proportion matters. The side effects that carry the most clinical weight with tirzepatide are gastrointestinal (nausea, vomiting, diarrhoea, reflux) and the more serious but rare ones: signs of pancreatitis (severe stomach pain radiating to the back), gallbladder symptoms, or significant allergic reactions. Nasal congestion sits well below all of those on any clinical priority list. For a full picture of what to watch for across the whole side-effect profile, the Mounjaro indigestion and GI symptoms page is a useful companion read, as the gut-related effects share some of the same timing patterns.

The reason to take nasal symptoms seriously at all isn't because they're dangerous; it's because they're manageable, and your prescriber can help you decide whether they warrant anything beyond watchful waiting. That's exactly what aftercare is for. If you haven't yet started treatment and are weighing up whether the side-effect profile is right for you, our page covering common Mounjaro questions is a good place to work through any remaining uncertainties before you take the next step. Check your eligibility with our prescribers and get your questions answered before you begin.