Semaglutide vs Tirzepatide vs Retatrutide: A Research Comparison

Quick comparison

Semaglutide is a selective GLP-1 receptor agonist developed by Novo Nordisk with a half-life of approximately seven days. Tirzepatide is a dual GLP-1 and GIP receptor agonist from Eli Lilly with a half-life of approximately five days. Retatrutide is a triple GLP-1, GIP and glucagon receptor agonist from Eli Lilly with a half-life of approximately six days. All three were studied as once weekly subcutaneous injections in clinical trials.

The maximum studied doses in obesity research were 2.4 mg for semaglutide, 15 mg for tirzepatide and 12 mg for retatrutide. Semaglutide and tirzepatide hold marketing authorisation for weight management. Retatrutide remains in phase 3 and is not approved.

What semaglutide is

Semaglutide is a synthetic glucagon-like peptide-1 analogue developed by Novo Nordisk. It shares 94% structural homology with native human GLP-1 and carries two key modifications: an amino acid substitution at position 8 that confers resistance to dipeptidyl peptidase-4 degradation, and a C-18 fatty diacid chain that enables albumin binding and extends the plasma half-life to approximately seven days.

Semaglutide was first authorised for type 2 diabetes in 2017 and subsequently for chronic weight management in 2021 at a higher weekly dose. It remains the most extensively studied incretin based compound, with a large indexed literature and a real world evidence base spanning multiple countries.

What tirzepatide is

Tirzepatide is a synthetic peptide engineered by Eli Lilly to activate two incretin receptors at once: the GLP-1 receptor and the glucose dependent insulinotropic polypeptide receptor. It is based on the native GIP sequence with modifications that confer GLP-1 receptor affinity, and it was the first authorised dual agonist in its class.

The molecule carries a C-20 fatty diacid moiety for albumin binding, giving a half-life of approximately five days. It was authorised for type 2 diabetes in 2022 and for chronic weight management in 2023. The rationale for dual agonism is that GIP receptor activation complements GLP-1 signalling through additional effects on adipose tissue metabolism and energy expenditure, which may explain the greater weight reduction reported compared with GLP-1 agonism alone.

What retatrutide is

Retatrutide (LY3437943) is a single molecule triple agonist developed by Eli Lilly that activates the GLP-1, GIP and glucagon receptors. Glucagon signalling was observed in preclinical models to promote hepatic lipid oxidation and increase energy expenditure, which may contribute to greater fat mass reduction than GLP-1 and GIP agonism alone.

The compound is a 39 amino acid peptide with a half-life of approximately six days. As of 2026 it holds no marketing authorisation and remains investigational. Phase 2 results were published in 2023 and topline phase 3 data from the TRIUMPH-1 trial were announced in May 2026, with peer reviewed publication still awaited. Our retatrutide research overview covers the compound on its own.

Mechanism of action across three generations

The three compounds can be read as successive generations of incretin based pharmacology, each engaging a broader receptor profile.

All three activate the GLP-1 receptor, which mediates appetite signalling through hypothalamic pathways, delays gastric emptying and enhances glucose dependent insulin secretion. In preclinical models, GLP-1 receptor activation was observed to reduce food intake through both central and peripheral routes.

The addition of GIP receptor agonism in tirzepatide and retatrutide introduces effects on adipose tissue that GLP-1 signalling alone does not produce. In animal models, GIP receptor activation was observed to influence lipid metabolism in white adipose tissue and to interact with thermogenic capacity in brown adipose tissue. The GIP receptor is also expressed in the central nervous system, where it may contribute to appetite regulation through mechanisms distinct from GLP-1.

Retatrutide uniquely engages the glucagon receptor. In preclinical research, glucagon receptor activation was observed to increase hepatic lipid oxidation, raise resting energy expenditure and promote amino acid catabolism. Glucagon receptor activity also carries a theoretical concern around hepatic glucose output, which appears in the published work to be counterbalanced by the concurrent GLP-1 and GIP activity of the triple agonist design.

Receptor activation summary

• Semaglutide: GLP-1 receptor only. Appetite signalling and modest changes in energy expenditure.
• Tirzepatide: GLP-1 and GIP receptors. Adds adipose tissue effects and moderate changes in energy expenditure.
• Retatrutide: GLP-1, GIP and glucagon receptors. Adds hepatic lipid oxidation and the most pronounced changes in energy expenditure reported in this class.

Clinical research findings compared

In the STEP 1 trial, 1,961 adults with obesity or overweight without diabetes were randomised to semaglutide 2.4 mg weekly or placebo. At 68 weeks the semaglutide group showed a mean body weight reduction of 14.9% against 2.4% with placebo, and 32% of participants reached a reduction of 20% or more. The STEP 5 trial reported approximately 15.2% reduction sustained at two years.

The SURMOUNT-1 trial enrolled 2,539 adults with obesity or overweight without diabetes. At 72 weeks, tirzepatide at 15 mg produced a mean reduction of 20.9%, and 22.5% in the completer population, against 3.1% with placebo. Among completers, 55% reached 20% or more and 36% reached 25% or more. SURMOUNT-4 reported that continued treatment maintained the reduction while participants switched to placebo regained a significant proportion.

In the phase 2 trial published in 2023, 338 adults with obesity received retatrutide at doses up to 12 mg. At 48 weeks the 12 mg group showed a mean reduction of 24.2%, with 26% of participants losing more than 30% of body weight. Topline results from the phase 3 TRIUMPH-1 trial, announced in May 2026, reported a mean 28.3% reduction at 80 weeks at the 12 mg dose, rising to 30.3% at 104 weeks, with 45.3% of participants reaching 30% or more at 80 weeks.

Head to head and indirect comparisons

No single randomised trial has compared all three compounds. Several indirect comparisons are available.

A real world retrospective cohort study by Rodriguez et al. (2024) compared semaglutide and tirzepatide in adults with overweight or obesity without diabetes. After adjustment for confounders, tirzepatide was associated with significantly greater weight reduction at matched timepoints.

A Bayesian network meta-analysis by Sinha and Ghosal (2025) across 19 randomised trials and 29,506 participants compared GLP-1 receptor agonists, dual agonists and retatrutide. Retatrutide and dual agonists reported an equivalent mean reduction of 11.0 kg, ahead of GLP-1 receptor agonists at 9.0 kg. Retatrutide stood out on threshold outcomes, with an odds ratio of 54.6 for reaching a reduction of 15% or more against 16.4 for dual agonists and 9.0 for GLP-1 receptor agonists.

Cardiovascular outcomes

Semaglutide is the only one of the three with completed cardiovascular outcomes data. The SELECT trial, with 17,604 participants, reported a 20% reduction in major adverse cardiovascular events in adults with pre-existing cardiovascular disease and overweight or obesity, without diabetes.

Tirzepatide cardiovascular outcomes are being collected in the ongoing SURPASS-CVOT trial, while interim data from the SUMMIT programme documented reverse left ventricular remodelling in participants with obesity related heart failure with preserved ejection fraction.

No cardiovascular outcomes trial has been completed for retatrutide, although the TRIUMPH-Outcomes trial is under way.

Safety signals compared

All three compounds share a class wide gastrointestinal adverse event profile driven primarily by GLP-1 receptor agonism. Frequency and severity were observed to track with dose and with the number of receptors engaged.

In pivotal trials, nausea was reported in 44.2% of participants on semaglutide 2.4 mg, 24.6% to 31.0% on tirzepatide 15 mg and 28.6% to 42.4% on retatrutide 12 mg. Diarrhoea was reported in 31.5%, 17.0% to 23.0% and 25.2% to 34.1% respectively. Vomiting was reported in 24.8%, 9.0% to 13.0% and 10.6% to 25.3%. Discontinuation for adverse events was approximately 7% for semaglutide, 4.3% to 7.1% for tirzepatide and 4.1% to 11.3% for retatrutide depending on dose.

Semaglutide has the most extensive long term safety record, with gallbladder related events reported above placebo rates in the STEP programme. Tirzepatide showed a generally milder gastrointestinal profile. Retatrutide uniquely showed a dysaesthesia signal in 20.9% of participants at the 12 mg dose, together with heart rate increases attributed to the glucagon component.

Practical research considerations

As of September 2026, semaglutide and tirzepatide are authorised for weight management by the FDA and the EMA, while retatrutide remains in phase 3. Research grade material is supplied lyophilised and documented by a batch report, and the guide to reading a peptide COA sets out how to check identity, purity and peptide content.

All three are kept refrigerated at 2 to 8 degrees Celsius before use and shielded from light, as described in the storage guide. Reconstitution with bacteriostatic water follows the routine in the reconstitution guide: bring the vial to room temperature, direct the stream against the vial wall, swirl rather than shake, then keep the preparation refrigerated and avoid repeated freeze and thaw cycles. Published stability data for retatrutide are limited, so general peptide handling applies.

European sourcing questions, from EU dispatch to batch documentation and customs, are covered in the European buyer's checklist.

Choosing a compound for investigation

Semaglutide suits research focused on well characterised GLP-1 receptor pharmacology, cardiovascular outcomes, long term safety or real world effectiveness. It is the benchmark against which newer agents are compared.

Tirzepatide suits research focused on dual incretin agonism, the combined effects of GLP-1 and GIP co-activation, or body composition endpoints. It reported greater weight reduction than semaglutide in both controlled and real world settings with a comparable or milder gastrointestinal profile.

Retatrutide suits research focused on multi receptor agonism, the metabolic effect of glucagon receptor activation alongside incretin signalling, or maximal weight reduction endpoints. Its evidence base is the least mature of the three and its dysaesthesia and heart rate signals require further characterisation.

Research use only

Compounds discussed here and supplied by Vitality Peps are for in vitro laboratory research only. They are not medicines, not supplements and not for human or veterinary consumption. Nothing above is dosing guidance or a recommendation for human use, and all compounds remain subject to the regulations of your jurisdiction.