The Lancet SURPASS Trials: A Deep Dive into Tirzepatide Dual GIP/GLP-1 Agonism

Lancet Insights | 2026-07-13 | 15 min read

Comprehensive analysis of The Lancet-published SURPASS clinical trial programme for tirzepatide, covering SURPASS-1 through SURPASS-5, cardiovascular outcomes, and dual GIP/GLP-1 agonism mechanisms.

The SURPASS Clinical Programme: Redefining Incretin Therapy

The SURPASS clinical trial programme represents one of the most comprehensive diabetes and obesity research initiatives in recent decades. Published extensively in The Lancet and JAMA, these trials established tirzepatide as a transformative therapeutic in metabolic medicine.

SURPASS Programme Overview

Trial Design

The SURPASS programme comprised five pivotal Phase 3 trials:

  • **SURPASS-1**: Monotherapy versus placebo in metformin-naive patients
  • **SURPASS-2**: Head-to-head versus semaglutide
  • **SURPASS-3**: Versus insulin glargine in patients with inadequate metformin response
  • **SURPASS-4**: Versus insulin glargine in patients with cardiovascular risk
  • **SURPASS-5**: Versus placebo in patients on basal insulin

Patient Populations

Over 10,000 patients participated across the programme, providing robust efficacy and safety data across:

  • Treatment-naive type 2 diabetes patients
  • Patients on oral agent combinations
  • Patients on basal insulin
  • Patients with established cardiovascular disease

Key SURPASS Findings

SURPASS-2: Head-to-Head Versus Semaglutide

This landmark comparative trial demonstrated tirzepatide's superiority:

HbA1c Results: | Dose | Tirzepatide | Semaglutide 1mg | Difference | |------|-------------|-----------------|------------| | 5mg | -1.87% | -1.86% | +0.01% | | 10mg | -2.07% | -1.86% | +0.21% | | 15mg | -2.46% | -1.86% | +0.60% |

Body Weight Results: | Dose | Tirzepatide | Semaglutide 1mg | Difference | |------|-------------|-----------------|------------| | 5mg | -7.6kg | -6.2kg | -1.4kg | | 10mg | -10.3kg | -6.2kg | -4.1kg | | 15mg | -12.4kg | -6.2kg | -6.2kg |

The 15mg dose produced approximately double the weight loss of semaglutide 1mg, establishing the dual agonism advantage.

SURPASS-3: Cardiovascular Comparator

SURPASS-3 demonstrated superior glycaemic control versus insulin glargine:

  • Mean HbA1c reduction of 2.1% with tirzepatide 10mg
  • Mean HbA1c reduction of 1.1% with insulin glargine
  • Significant body weight reduction versus weight gain with insulin
  • Lower hypoglycaemia rates with tirzepatide

SURPASS-4: Cardiovascular Risk Population

In high cardiovascular risk patients:

  • Tirzepatide demonstrated favourable cardiovascular safety profile
  • Numerical reduction in MACE (major adverse cardiovascular events)
  • Significant improvements in cardiovascular risk factors
  • Ongoing SURPASS-CVOT for definitive cardiovascular outcomes

Dual GIP/GLP-1 Mechanism

GIP Receptor Pharmacology

Glucose-dependent insulinotropic polypeptide (GIP) is an incretin hormone secreted from K-cells in the duodenum and proximal jejunum. GIP receptor agonism contributes to tirzepatide's effects through:

Metabolic Effects:

  • Enhanced postprandial insulin secretion (glucose-dependent)
  • Promotion of lipid storage in subcutaneous adipose tissue
  • Regulation of bone metabolism
  • Potential effects on food reward pathways

Why Dual Agonism Matters

The combination of GIP and GLP-1 agonism creates complementary effects:

  • **GLP-1**: Primary appetite suppression, gastric emptying delay
  • **GIP**: Enhanced energy partitioning, fat metabolism
  • **Combined**: Greater overall metabolic benefit

Research suggests GIP agonism may prevent the compensatory mechanisms that limit weight loss with selective GLP-1 agonism alone.

Safety Profile

Common Adverse Events

The SURPASS programme established tirzepatide's safety profile:

  • **Gastrointestinal**: Nausea (18-22%), diarrhoea (13-15%), vomiting (8-10%)
  • **Injection site reactions**: Rare (<2%)
  • **Hypoglycaemia**: Primarily when combined with sulfonureas or insulin

Discontinuation Rates

Tirzepatide demonstrated favourable tolerability:

  • Discontinuation rates lower than semaglutide in head-to-head comparison
  • Most adverse events mild-to-moderate severity
  • GI symptoms typically transient, decreasing over time

Clinical Implications

Paradigm Shift in Diabetes Care

The SURPASS results have transformed treatment algorithms:

  • **First-line intensification**: Dual agonism now preferred over GLP-1 monotherapy
  • **Weight loss emphasis**: Body weight as primary efficacy endpoint
  • **Combination potential**: Ongoing studies with basal insulin, SGLT2 inhibitors

Obesity Indication

Based on SURPASS weight loss data, tirzepatide received regulatory approval for obesity:

  • Mean body weight reduction of 15-20% at highest doses
  • Responders (≥10% weight loss) exceeding 70% of patients
  • Improvements in cardiometabolic risk factors
  • Potential for expanded cardiovascular indications

Research Applications

Quality Requirements

Metabolic research with tirzepatide requires:

  • HPLC purity ≥99.5% for reproducible in vitro studies
  • Mass spectrometry sequence verification
  • Batch-specific COA documentation
  • Proper storage conditions (-20°C)
  • Endotoxin testing for in vivo applications

Concentration Ranges

Research concentrations vary by application:

  • In vitro receptor studies: 0.01-100 nM
  • In vivo preclinical: 0.1-10 mg/kg
  • Human equivalent dosing calculations required

Ongoing Research

The SURPASS programme continues with:

  • SURPASS-CVOT: Cardiovascular outcomes trial
  • SURMOUNT: Obesity-specific trials (SURMOUNT-1, 2, 3, 4)
  • Combination studies with amylin analogues
  • Fixed-dose combination development

ZePeptide provides research-grade tirzepatide with complete analytical documentation for metabolic research programmes.

ZePeptide content is for lawful laboratory and in-vitro research sourcing. Products are not supplied for human or veterinary use.

Research peptide catalogSupplier checklistMore peptide guides