Can weight loss injections cause kidney stones?

What clinical trials and regulatory guidance have found so far

The large phase-3 trials (SURMOUNT-1 for tirzepatide and STEP 1 for semaglutide) were not designed to detect kidney stone formation as a primary endpoint, so the absence of a signal there does not settle the question definitively. What they do show is that kidney function, measured by eGFR and urine albumin-to-creatinine ratio, held stable or improved in most participants over the study period. The NHS medicines information for tirzepatide does not list kidney stones among the recognised side effects, and the same is true of the NHS semaglutide page. The MHRA's ongoing pharmacovigilance includes the Black Triangle monitoring applied to both medicines, which means any emerging signal would be captured and communicated via a Drug Safety Update. That transparency is worth knowing about.

Where the picture is genuinely less clear is in sub-populations. People with pre-existing kidney stone disease, those who form uric acid or calcium oxalate stones, and those who are prone to dehydration may face a different risk profile from participants in the general trials. That uncertainty is not a reason to avoid treatment; it is a reason to discuss it properly. Our detailed look at weight loss injections and kidney stones covers the emerging evidence in full.

The dehydration pathway — the risk that is most concrete

The clearest mechanism worth taking seriously is dehydration. Nausea, vomiting, and reduced appetite are among the most commonly reported early side effects of both tirzepatide and semaglutide, particularly in the first few weeks of treatment or after a dose increase. If fluid intake drops significantly during this period, urine becomes more concentrated, and concentrated urine is a well-established precursor to stone formation in people who are susceptible.

This is not a theoretical concern. The MHRA's January 2026 Drug Safety Update for GLP-1 medicines highlighted acute kidney injury as a potential consequence of severe gastrointestinal illness during treatment, driven largely by dehydration. The practical message is straightforward: staying well hydrated matters especially in the weeks your body is adjusting. If vomiting is frequent or prolonged, contact your prescriber rather than waiting for your next scheduled review. A question our prescribers hear regularly is whether pausing the medicine during a period of illness is appropriate, the answer depends on individual circumstances, so early contact is always the right move.

For a broader picture of how these medicines interact with kidney function, our page on weight loss injections and kidney problems covers acute and longer-term renal considerations.

Weight loss itself, diet shifts, and urinary chemistry

Rapid weight loss, by any method, changes urinary composition. Fat metabolism increases urinary oxalate excretion in some people; protein intake patterns shift; uric acid excretion can rise. These are the same changes that bariatric surgery programmes monitor closely, and they are worth knowing about on any effective weight-loss treatment. The SURMOUNT-1 trial recorded average body-weight reductions of around 20–21% at the 15mg tirzepatide dose over 72 weeks, published in the New England Journal of Medicine, meaningful weight change that brings metabolic shifts alongside it.

Diet changes matter too. Eating less overall, cutting highly processed food, and increasing protein are all common alongside treatment, and each affects urinary chemistry differently. If you have a history of specific stone types, a renal dietitian can advise on foods that shift risk, something a prescriber can refer you to. People who have already been told they are prone to kidney stones should also consider asking about hydration targets specifically, not just general advice to drink more.

If pre-existing kidney disease is part of your history, the considerations are different again. Our page on weight loss injections and kidney disease addresses that clinical picture directly, as does our guidance on whether these medicines are appropriate when kidney disease is already present.

Who to speak to, and when

If you have never had a kidney stone and your kidney function is normal, the evidence available does not suggest kidney stones as a significant risk from weight loss injections. The sensible precaution is straightforward: keep your fluid intake up, report any prolonged vomiting to your prescriber promptly, and flag any history of stones before you begin.

If you have had kidney stones before, or if your GP has mentioned that you have raised oxalate or uric acid levels, raise this explicitly at your consultation. A prescriber can weigh up whether additional monitoring is appropriate. Never assume a prior stone history rules out treatment, it rarely does, but it does change how treatment is managed. For context on how different injections compare in this and other respects, our guide to choosing the right weight loss injection covers the clinical factors a prescriber considers.

Gallstones are a related concern worth raising at the same time, as rapid weight loss carries a recognised gallstone risk. Our page on weight loss injections and gallstones covers what is known there. And if you would like to understand how a nume consultation handles pre-existing medical history (including kidney conditions) the team at our clinical team can walk you through it. Ready to talk it through? Speak to our prescribers through a free consultation, and bring your full history with you.