Using Mounjaro long term: what the trial data and guidance actually tell us

What the 72-week trial data actually showed

The clearest starting point is SURMOUNT-1, the pivotal phase 3 trial of tirzepatide for weight management, published in the New England Journal of Medicine. Over 72 weeks, adults taking the 15mg dose achieved an average body-weight reduction of around 20–21%. That figure comes from a trial with 2,539 participants (thousands of adults, not a small sample) and it represents one of the largest average reductions recorded for a licensed weight-loss medicine. The results at lower maintenance doses were meaningfully smaller, which is why NICE's guidance, published in December 2024 and updated in September 2025, builds in a formal review point: if someone has not lost at least 5% of their body weight after six months at the highest dose they can tolerate, continuing treatment should be reassessed. That is not a punishment clause; it is an honest recognition that the medicine works well for most people and less well for some, and that continuing a treatment with limited personal benefit carries its own risk.

The trial also followed a sub-group through an extension phase. Participants who stopped tirzepatide regained a substantial proportion of the weight they had lost. This is consistent with what is known about obesity as a chronic condition: the underlying biology does not switch off because a medicine course ends. You can read more about what long-term studies on Mounjaro have examined beyond the 72-week window.

Can you take Mounjaro long term, and what does the licence say?

The short answer is yes, within the terms of the UK marketing authorisation. Mounjaro is licensed as a long-term weight-management medicine for eligible adults, it is not licensed for a fixed maximum duration the way some medicines are. Compare this with Wegovy (semaglutide), for which NICE's recommendation (TA875) explicitly caps NHS use at two years within specialist services. No equivalent two-year cap appears in NICE's tirzepatide recommendation (TA1026). That does not mean treatment continues automatically or without clinical justification; it means the framework does not time-limit it by default.

Whether you can stay on Mounjaro long term in practice depends on response, tolerability, and any changes in your health. Private prescribers (including those at a GPhC-registered pharmacy) assess this before every repeat order. There is no auto-renewal. The prescriber looks at evidence of ongoing response and any relevant safety signals each time, which is exactly how a medicine carrying a Black Triangle designation (indicating that Mounjaro is subject to additional MHRA monitoring) should be managed.

Side effects and safety over extended tirzepatide use

The most common side effects during long-term tirzepatide use are gastrointestinal: nausea, constipation, loose stools, indigestion, and sometimes burping. For most people these are most noticeable at the start of each dose step and settle within days to a couple of weeks. They do not typically worsen over months of stable dosing, if anything, tolerability tends to improve once titration is complete and the dose is steady.

Pancreatitis is worth knowing about. The MHRA issued a Drug Safety Update in January 2026 highlighting acute pancreatitis as a known but infrequent risk with GLP-1 medicines: severe, persistent stomach pain, particularly if it radiates to the back, warrants urgent medical attention. This applies whether you have been on treatment for three weeks or three years. For a fuller picture of what is known and what remains under study, the long-term effects of Mounjaro page covers the safety data in detail, and there is a separate page addressing the specific question of Mounjaro's long-term effects and cancer risk for those who want to look at that area of ongoing research. The NHS also publishes patient-level guidance on tirzepatide covering when to seek medical help. Report any suspected side effects via the MHRA Yellow Card scheme.

Interactions with other medicines are relevant over a long course too. Because tirzepatide slows gastric emptying, the absorption of oral medicines can be affected, oral contraceptives are a practical example, and women on the pill should discuss this with their prescriber. The interaction between prednisolone and Mounjaro is another question that comes up in clinical practice, particularly for people managing inflammatory conditions alongside weight.

What long-term clinical review looks like in private practice

People sometimes ask whether they will have to keep paying indefinitely. The honest answer is that treatment cost over time is a real consideration, and the Mounjaro price page lays out what private prescriptions cost and what that includes. More practically: long-term use is not a passive commitment. At a well-run service, each repeat order involves a genuine clinical re-review, not a rubber stamp. A prescriber checks that the medicine is still working, that no new contraindications have emerged, and that the dose remains appropriate.

The pattern that works best for most people on long-term tirzepatide use combines the medicine with sustained changes to eating and activity. That is not a caveat added for regulatory reasons; it is what the trial design showed and what the licence reflects. The medicine reduces appetite and slows gastric emptying, it does not replace the habits that determine what happens next. If you are thinking about starting, or wondering whether you are a candidate for long-term treatment, a free consultation with one of our prescribers is the right first step. They review every case the same day, a real clinician reads your answers, not software.