SURPASS-3 and tirzepatide: what the trial actually showed

Step 1: understanding what SURPASS-3 was designed to test

Most large drug trials recruit people who are relatively medication-free at baseline. SURPASS-3 took a different approach. It enrolled around 1,400 adults with type 2 diabetes who were already established on basal insulin, a population whose blood sugar is harder to control and whose clinical management is genuinely complex. The primary question was whether switching to tirzepatide (5mg, 10mg or 15mg, titrated over the first 20 weeks) could improve HbA1c more effectively than continuing and adjusting insulin degludec over 52 weeks.

That design matters for interpreting the results. These were not newly diagnosed patients; they were people whose diabetes had progressed to the point where insulin was already part of daily life. Demonstrating a meaningful benefit in that group set a higher bar than many earlier phase 3 studies.

The trial sits inside the broader SURPASS clinical programme, which evaluated tirzepatide across several different diabetes populations and comparators. SURPASS-3 was specifically the insulin-comparator arm, and understanding that context is essential before drawing wider conclusions.

Step 2: what the 52-week results showed

At 52 weeks, all three tirzepatide doses produced greater reductions in HbA1c than insulin degludec. The 15mg dose achieved the largest average reduction. Body weight also fell in the tirzepatide groups, while participants on insulin degludec on average gained a small amount of weight over the same period, a pattern consistent with the known pharmacology of basal insulin.

Hypoglycaemia rates were lower with tirzepatide than with insulin degludec, which is clinically relevant for people managing diabetes day to day. The NHS patient information for tirzepatide notes that low blood sugar is a recognised risk when tirzepatide is used alongside insulin or insulin secretagogues, so the prescriber's role in reviewing that combination is significant.

Side effects followed the profile seen across the SURPASS programme: gastrointestinal symptoms (nausea, diarrhoea and reduced appetite) were the most commonly reported, tended to peak early in titration and settled for most people over the following weeks. Injection-site reactions were also recorded.

If you are curious how these findings compare with the diabetes-free obesity population, the SURPASS-1 trial provides a useful reference point, as it studied tirzepatide as monotherapy without any background insulin.

Step 3: how SURPASS-3 connects to the UK licensing and NICE picture

It is worth being clear about what SURPASS-3 was and was not. The trial measured diabetes outcomes; it was not a weight-management study. Tirzepatide holds a UK licence for weight management (as Mounjaro) and for type 2 diabetes, and if you want a fuller picture of how the medication works across both indications, our SURPASS tirzepatide page covers the key details in one place. The SURPASS programme supported the diabetes indication, while the SURMOUNT programme, in adults with obesity, supported the weight-management licence.

If you are researching tirzepatide primarily for weight loss rather than diabetes management, the weight-management evidence is described in detail on the tirzepatide overview page. NICE evaluated the weight-management use in Technology Appraisal TA1026, recommending tirzepatide for adults with a BMI of 35 or above alongside at least one weight-related condition, with lower BMI thresholds recognised for some ethnic backgrounds under UK guidance.

The cost of private tirzepatide treatment is a question many people arrive at quickly, a straightforward overview of what to expect is on our Mounjaro price comparison page. For context on the full trial programme that generated the evidence base, the SURPASS study overview brings together the individual trials in one place.

If SURPASS-3 caught your attention because you or someone you care for manages both type 2 diabetes and excess weight, the conversation belongs with a prescriber who can weigh up the full picture. Our clinical team, led by Independent Prescriber Mostafa Damghani, reviews each consultation personally. If you would like to understand whether tirzepatide is suitable for you, you can check your eligibility through a free consultation, no waiting list, reviewed the same day.