CagriSema vs Mounjaro: What the New Phase 3 Trial Really Shows

For the first time, a Phase 3 trial has put Novo Nordisk’s investigational weight-loss treatment CagriSema directly against tirzepatide, the medicine sold in the UK as Mounjaro, and reported that CagriSema came out ahead on weight loss. That has made CagriSema vs Mounjaro one of the most talked-about comparisons in UK weight-loss conversations this week.

On 21 September 2026, Novo Nordisk announced that in its REIMAGINE 5 trial, CagriSema produced greater average weight loss than tirzepatide in adults with type 2 diabetes.

It is a genuine head-to-head result, and it matters. But the headline needs one important detail added: the tirzepatide dose used in the trial was 5 mg, one of the lower doses of Mounjaro used in the UK.

That detail changes what the result can and cannot tell us.

Evidence note: The REIMAGINE 5 and REDEFINE 9 figures in this article are topline results announced by Novo Nordisk. They have not yet been published in full in a peer-reviewed journal. CagriSema is an investigational medicine and is not authorised in the UK. This article is not medical advice. Always speak to an appropriately qualified healthcare professional before making changes to your treatment.

What Has Novo Nordisk Announced?

Novo Nordisk announced topline results from two Phase 3 trials of CagriSema at its Capital Markets Day investor event on 21 September 2026.

REIMAGINE 5 compared once-weekly CagriSema 1.0 mg/1.0 mg with once-weekly tirzepatide 5 mg. It involved adults with type 2 diabetes whose blood sugar was not adequately controlled on metformin, an SGLT2 inhibitor, or both.

At 60 weeks, Novo Nordisk reported:

• Weight loss: an estimated average of 12.4% with CagriSema 1.0 mg/1.0 mg, compared with 9.1% with tirzepatide 5 mg. The company says this met the test for superiority.
• Blood sugar (HbA1c): a reduction of 1.71 percentage points with CagriSema, compared with 1.67 percentage points with tirzepatide 5 mg. The company says this showed CagriSema was non-inferior, meaning not meaningfully worse.

Novo Nordisk says these figures use the trial’s efficacy estimand, which estimates the treatment effect under the trial’s specified assumptions about treatment adherence. Results using the treatment-regimen estimand, which assesses the treatment effect regardless of treatment adherence, have not yet been released for REIMAGINE 5.

So Did CagriSema Beat Mounjaro?

Under the conditions of this trial, yes, in part. REIMAGINE 5 supports saying that CagriSema 1.0 mg/1.0 mg produced greater average weight loss than tirzepatide 5 mg over 60 weeks, in adults with type 2 diabetes, according to the company’s topline results.

On blood sugar, the two treatments performed similarly.

What the trial does not establish is that CagriSema is more effective than Mounjaro in general, or that it outperforms every dose of tirzepatide. Many people using Mounjaro in the UK take higher doses than 5 mg, and the trial did not test those doses.

So a headline such as “CagriSema beats Mounjaro” goes further than the evidence. A more accurate summary is: CagriSema beat tirzepatide 5 mg on weight loss in one Phase 3 trial in people with type 2 diabetes.

What Is CagriSema?

The names in this story can be confusing, so here is how they fit together:

• Semaglutide is a GLP-1 receptor agonist. It is the active ingredient in Wegovy and Ozempic.
• Cagrilintide (sometimes shortened to “Cagri”) is a long-acting amylin analogue. Amylin is a hormone involved in appetite and feeling full. Cagrilintide is investigational.
• CagriSema is Novo Nordisk’s investigational once-weekly combination of cagrilintide and semaglutide.
• Tirzepatide is Eli Lilly’s GIP and GLP-1 receptor agonist, sold in the UK as Mounjaro. It is a different medicine from a different company.

So CagriSema and Mounjaro both act on the GLP-1 pathway, but they add different second pathways: amylin for CagriSema, and GIP for Mounjaro.

For background on the amylin half of the combination, see our explainer Cagrilintide UK: What Is Cagri and Why Is Everyone Suddenly Talking About It? Our earlier guide, CagriSema UK: What Is It and When Is It Coming to Britain, covers the wider CagriSema story.

What Did REDEFINE 9 Show?

Novo Nordisk announced a second Phase 3 result on the same day. REDEFINE 9 compared CagriSema with placebo, alongside diet and exercise, in adults living with overweight or obesity.

At 68 weeks, the company reported an estimated average weight loss of 21.0% with CagriSema 1.0 mg/1.0 mg, compared with 2.0% with placebo.

The trial also tested a CagriSema 1.7 mg/1.7 mg dose, but Novo Nordisk’s announcement did not give a weight-loss figure for that dose. The company also reported greater improvements than placebo in systolic blood pressure, waist-to-height ratio and blood fats.

REDEFINE 9 did not include tirzepatide, so it tells us nothing directly about CagriSema vs Mounjaro. It is a placebo-controlled trial.

CagriSema vs Mounjaro: Why the Tirzepatide Dose Matters

In the UK, Mounjaro is started at 2.5 mg once weekly and increased to 5 mg after four weeks. According to the UK prescribing information, adult maintenance doses are 5 mg, 10 mg or 15 mg, with 15 mg the maximum.

REIMAGINE 5 compared CagriSema with 5 mg, the lowest of those maintenance doses. It also used a lower CagriSema dose (1.0 mg/1.0 mg) than the 2.4 mg/2.4 mg dose in Novo Nordisk’s main obesity trials. In effect, the trial compared lower doses of both treatments.

We already have a head-to-head result at the top doses, and it points the other way. In February 2026, Novo Nordisk reported that in REDEFINE 4, an 84-week open-label trial in 809 people with obesity, CagriSema 2.4 mg/2.4 mg did not meet its main goal of showing non-inferior weight loss compared with tirzepatide 15 mg. Weight loss was 23.0% with CagriSema and 25.5% with tirzepatide 15 mg if everyone had stayed on treatment (20.2% vs 23.6% counting everyone as randomised).

REDEFINE 4 involved a different population (people with obesity, rather than type 2 diabetes), different doses and a different trial length, so the two results cannot be combined into a single ranking. Together, though, they show why the dose matters so much when reading a “CagriSema vs Mounjaro” headline.

What About Side Effects?

For REIMAGINE 5 and REDEFINE 9, Novo Nordisk said only that CagriSema was “well tolerated overall”, with a safety profile consistent with previous studies. The company has not yet released detailed side-effect rates for either trial.

The fullest published picture comes from the earlier REDEFINE 1 trial, published in the New England Journal of Medicine in 2025. Gastrointestinal side effects such as nausea, vomiting, diarrhoea, constipation and abdominal pain were reported by 79.6% of people taking CagriSema, compared with 39.9% taking placebo. Most were mild to moderate and temporary.

Detailed safety data from the new trials, including how often people stopped treatment because of side effects, will matter when the full results are published.

Is CagriSema Available in the UK?

No. CagriSema is an investigational medicine. We could not identify a UK marketing authorisation for it, and it cannot be prescribed as a licensed medicine in the UK.

Novo Nordisk submitted CagriSema to the US Food and Drug Administration (FDA) in December 2025, for weight management at the 2.4 mg/2.4 mg dose. The company says it expects a decision in the fourth quarter of 2026. We could not identify a publicly announced submission to the UK’s Medicines and Healthcare products Regulatory Agency (MHRA).

New trial results do not change a medicine’s legal status. Any product sold online as “CagriSema” or “Cagri” is not an authorised UK medicine and should not be assumed to be the same as the product studied in Novo Nordisk’s trials.

What Does This Mean for Mounjaro?

Mounjaro is authorised in the UK for type 2 diabetes and for weight management in eligible adults, and it has a large published evidence base.

REIMAGINE 5 does not change that. It is one company-announced result, against one dose of tirzepatide, in one group of patients. It does not show that people doing well on Mounjaro would do better on CagriSema, and CagriSema is not available as an alternative in the UK.

For a plain-English overview of the medicine itself, see our Mounjaro UK guide.

Why This Result Matters

Head-to-head trials between competing weight-loss medicines are still unusual. Most comparisons people see online are made across separate trials with different patients, doses and timescales, which makes them unreliable.

REIMAGINE 5 is a direct comparison within a single Phase 3 trial, so it is more informative than a cross-trial comparison. It shows that, at the doses tested and in this population with type 2 diabetes, CagriSema produced greater average weight loss than tirzepatide 5 mg, with similar reductions in HbA1c.

REDEFINE 9 adds evidence that CagriSema can produce substantial weight loss at a lower dose than the 2.4 mg/2.4 mg dose submitted to the FDA.

For how the currently available options compare, see our guide Weight Loss Jabs & Pills Compared: What the Real Data Shows.

What We Still Do Not Know

Several important questions remain open:

• The full results of REIMAGINE 5 and REDEFINE 9 have not been published or independently peer reviewed.
• Results counting everyone who stopped or changed treatment (the treatment-regimen estimand) have not yet been released for these trials.
• Detailed side-effect and discontinuation rates are not yet available.
• We do not know how CagriSema would compare with tirzepatide 10 mg or 15 mg in people with type 2 diabetes.
• We do not know which CagriSema doses, if any, will be authorised, or when.
• No UK regulatory timetable has been announced.

What This Means for People in the UK

Four points are worth keeping in mind:

REIMAGINE 5 is a real head-to-head Phase 3 result, and CagriSema came out ahead on weight loss.

The comparison was with tirzepatide 5 mg, not with every dose of Mounjaro.

At the top doses, in REDEFINE 4, CagriSema did not match tirzepatide 15 mg.

CagriSema is investigational and is not authorised in the UK.

If you are currently prescribed Mounjaro or another weight-loss medicine, news about an unapproved treatment is not in itself a reason to stop or change what you are taking. Any change should be discussed with your prescriber.

Key Takeaways

• On 21 September 2026, Novo Nordisk announced that CagriSema 1.0 mg/1.0 mg produced an estimated 12.4% average weight loss at 60 weeks, compared with 9.1% for tirzepatide 5 mg, in the Phase 3 REIMAGINE 5 trial.
• The trial involved adults with type 2 diabetes inadequately controlled on metformin, an SGLT2 inhibitor, or both. HbA1c fell by 1.71 percentage points with CagriSema and 1.67 with tirzepatide 5 mg.
• The result supports CagriSema outperforming tirzepatide 5 mg on weight loss in this trial. It does not show that CagriSema beats Mounjaro at every dose.
• In the earlier REDEFINE 4 trial, CagriSema 2.4 mg/2.4 mg did not meet its goal of non-inferior weight loss compared with tirzepatide 15 mg.
• REDEFINE 9 reported an estimated 21.0% average weight loss with CagriSema 1.0 mg/1.0 mg at 68 weeks, compared with 2.0% with placebo, in adults with overweight or obesity.
• The new figures are company-announced topline results and have not yet been published in full.
• CagriSema combines cagrilintide (an amylin analogue) with semaglutide (the active ingredient in Wegovy and Ozempic). Mounjaro is tirzepatide, a different medicine.
• CagriSema is investigational and is not authorised in the UK. An FDA decision is expected in the fourth quarter of 2026.

Further Reading

Cagrilintide UK: What Is Cagri and Why Is Everyone Suddenly Talking About It?

CagriSema UK: What Is It and When Is It Coming to Britain

Mounjaro UK — The Complete Plain English Guide

Weight Loss Jabs & Pills Compared: What the Real Data Shows

Sources

Novo Nordisk (21 September 2026) — Novo’s CagriSema delivers superior weight loss versus tirzepatide in REIMAGINE 5 trial

Novo Nordisk (23 February 2026) — CagriSema demonstrated 23% weight loss in the open-label head-to-head REDEFINE 4 trial; primary endpoint not achieved

Novo Nordisk (18 December 2025) — Novo Nordisk files for FDA approval of CagriSema

Garvey et al. (2025), New England Journal of Medicine — Coadministered Cagrilintide and Semaglutide in Adults with Overweight or Obesity (REDEFINE 1)

Electronic Medicines Compendium — Mounjaro KwikPen (tirzepatide) Summary of Product Characteristics

Healio (21 September 2026) — CagriSema bests tirzepatide for weight loss in adults with type 2 diabetes

This article reports company-announced clinical trial results and does not constitute medical advice. CagriSema is an investigational medicine and is not authorised in the UK. Individual circumstances vary. Always speak to an appropriately qualified healthcare professional before making changes to your treatment or considering any new medicine.