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Retatrutide vs Tirzepatide

A South African research-buyer's comparison of the triple-agonist retatrutide and dual-agonist tirzepatide — mechanism, trial evidence, evidence maturity, formats and price.

The core difference is mechanical. Retatrutide is a triple agonist — one molecule that activates three receptors at once (GIP, GLP-1 and glucagon) — while tirzepatide is a dual agonist that activates two (GIP and GLP-1). In its phase-2 obesity trial retatrutide produced the largest average weight reduction reported for any incretin agonist so far (about 24% at 48 weeks at the top dose), edging past tirzepatide's headline obesity figure (about 21% at 72 weeks). The decisive caveat is maturity: retatrutide's evidence is early — a single phase-2 study — whereas tirzepatide rests on a large phase-3 programme. For a South African research buyer, retatrutide suits protocols exploring the newest triple-pathway mechanism and the largest modelled effect, and tirzepatide suits those wanting the more thoroughly characterised, phase-3-backed comparator.

Both are stocked at BeSkinny as research-grade peptides in the weight-loss injections range. This guide compares mechanism, trial evidence, evidence maturity, side effects, formats and price so you can specify the right compound, all framed for laboratory and research use, not human treatment. For the next rung down the agonist ladder, the sibling tirzepatide vs semaglutide guide covers the dual-versus-single comparison.

Retatrutide vs tirzepatide at a glance

The table condenses the practical differences. Figures describe what the peer-reviewed obesity trials and drug references report; they are not outcomes you should expect or a dosing protocol. The two have not been tested head-to-head, so the percentages below come from separate studies of different design, duration and stage.

Attribute Retatrutide Tirzepatide
Mechanism Triple agonist — activates the GIP, GLP-1 and glucagon receptors in one molecule Dual agonist — activates the GIP and GLP-1 receptors in one molecule
Trial weight-loss (mean) About 24% at 48 weeks at the top (12 mg) dose in a phase-2 trial (Jastreboff 2023); dose-dependent, earlier-stage evidence About 15% to 21% at 72 weeks across doses (SURMOUNT-1); backed by a larger phase-3 programme
Research dose cadence Once weekly, titrated upward over several weeks Once weekly, titrated upward over several weeks
Formats stocked Lyophilised vial (10 mg and 32 mg) and pre-filled pen (32 mg) Lyophilised vial and pre-filled pen (30 mg)
Reconstitution needed Vial: yes (add bacteriostatic water). Pen: no Vial: yes (add bacteriostatic water). Pen: no
Side-effect profile GI-predominant (nausea, diarrhoea, vomiting, constipation) GI-predominant (nausea, diarrhoea, vomiting, constipation)
Price at BeSkinny (ZAR) From about R1600 (vial); pens from about R2500 From about R1800 (vial); pens from about R2100

What each molecule is

Retatrutide: the triple GIP/GLP-1/glucagon agonist

Retatrutide is a synthetic peptide engineered to bind three receptors at once: glucose-dependent insulinotropic polypeptide (GIP), glucagon-like peptide-1 (GLP-1) and glucagon. The added glucagon arm is what makes it a triple agonist, and in research models that third pathway is associated with increased energy expenditure on top of the appetite and glucose effects shared across the incretin class. It is the newest of these molecules, which is why it is often called next-generation. Review the strengths stocked on the retatrutide category hub, with the HD Labs Retatrutide 32 vial the flagship SKU and the HD Labs Retatrutide 10 vial the lower-cost entry point.

Tirzepatide: the dual GIP/GLP-1 agonist

Tirzepatide binds two incretin receptors — GIP and GLP-1 — in a single molecule, which is why it is called a dual agonist or twincretin. It is the more established compound here, with a deeper and longer published record, and the usual reference point against which newer agonists like retatrutide are measured. See the tirzepatide category hub and the HD Labs Tirzepatide 30 vial for stocked options.

Evidence maturity: phase 2 versus phase 3

This is the most important line in the comparison, and it cuts in tirzepatide's favour. Retatrutide's headline number comes from a single, smaller, shorter study, while tirzepatide's rests on a broad late-stage programme.

  • Retatrutide (phase 2, Jastreboff 2023, NEJM). A 48-week trial of about 338 participants reported dose-dependent mean weight reductions of roughly 17% at 4 mg, 23% at 8 mg and 24% at the 12 mg dose, versus about 2% on placebo — and at the top dose roughly a quarter of participants lost 30% or more of body weight. Striking, but phase-2: fewer participants, a shorter window, with larger phase-3 confirmation still maturing.
  • Tirzepatide (phase 3, SURMOUNT-1, NEJM 2022). Over 72 weeks, mean body-weight reduction ranged from about 15% at the lower dose to about 21% at the top dose (with one trial estimand reporting up to about 22.5%), versus roughly 2% to 3% on placebo. This sits inside the wider phase-3 SURMOUNT obesity programme.
  • Tirzepatide in type 2 diabetes (SURPASS). The SURPASS trials reported large reductions in HbA1c alongside weight loss across a multi-study programme, deepening tirzepatide's late-stage evidence base.

So on the raw percentages retatrutide reports the higher figure, but the honest reading is that it is an earlier-stage compound whose numbers rest on far less data. These are group averages from separate clinical populations describing trends in the evidence base, not a promised result and not comparable as if from one trial.

Side effects: what trials report

By research convention we describe adverse events as they appear in the trial publications and drug references, not as medical advice. For both molecules the dominant category is gastrointestinal: nausea, diarrhoea, vomiting and constipation, most often mild to moderate and most common during dose escalation. Because both act on the GLP-1 pathway their side-effect character is broadly similar in class, and in each case the trials describe slower titration as the usual way these effects were managed. The retatrutide phase-2 paper additionally noted dose-related increases in heart rate. No head-to-head safety comparison of the two has been published, so relative tolerability cannot be stated with confidence.

Formats and how to buy in South Africa

BeSkinny stocks both molecules in two research formats, and the choice affects handling more than anything else.

Both molecules are temperature-sensitive, so BeSkinny ships them cold-chain with gel packs to preserve integrity in transit across South Africa. Payment is by EFT, card or Bitcoin, and placing an order requires a verified BeSkinny account. Browse everything side by side on the weight-loss injections hub. Prices drift with stock and supplier costs, so treat these figures as approximate and check the live product pages.

Which one to choose

The decision usually comes down to how much you value the newest mechanism and the largest reported effect against how mature you want the evidence to be.

  • Consider retatrutide if your protocol is exploring the triple GIP/GLP-1/glucagon mechanism, you want the largest average effect reported to date, and you accept that the supporting evidence is earlier-stage (phase 2).
  • Consider tirzepatide if you want the deeper, phase-3-backed documentation of a dual agonist, a well-characterised reference comparator, or a lower-risk read on the evidence.
  • Consider the vial over the pen when cost is the priority and you are comfortable reconstituting; choose the pen when you want a ready-mixed format and will pay for the convenience.

If you also want to see how the dual agonist compares one step further down, against a single-pathway GLP-1 molecule, the tirzepatide vs semaglutide guide maps that side of the landscape.

Research-use disclaimer

All products discussed are supplied strictly for laboratory and research purposes. Nothing on this page is medical advice, a treatment recommendation, or a human dosing protocol. The efficacy and safety figures describe what published clinical trials and public drug references report, cited following standard research-reference convention. BeSkinny supplies the molecules retatrutide and tirzepatide as research compounds; it does not sell branded consumer medicines.

Frequently asked questions

Is retatrutide stronger than tirzepatide?

On the raw numbers, retatrutide's phase-2 top dose reported a higher mean reduction (about 24% at 48 weeks) than tirzepatide's phase-3 figure (about 21% at 72 weeks). But they have never been compared in one trial, and retatrutide's evidence is far less mature — so "stronger" means a higher figure from a smaller, earlier study, not a proven advantage.

Why is retatrutide called a triple agonist?

Because it activates three receptors in one molecule — GIP, GLP-1 and glucagon — whereas tirzepatide activates two. The glucagon receptor is the added third pathway, associated in research with increased energy expenditure alongside the shared appetite and glucose effects.

Which one has more evidence behind it?

Tirzepatide, clearly. It sits on a large phase-3 programme across both obesity (SURMOUNT) and type 2 diabetes (SURPASS), while retatrutide's obesity data comes from a single phase-2 trial. If depth of published data matters to your protocol, tirzepatide is the more documented choice.

Which is cheaper at BeSkinny?

Retatrutide has the lower vial entry point, from about R1600 for the HD Labs Retatrutide 10 vial versus about R1800 for the HD Labs Tirzepatide 30 vial. Higher-strength vials and the pens cost more in both. Prices are approximate and can drift.

Sources

  • Jastreboff AM, et al. Triple-Hormone-Receptor Agonist Retatrutide for Obesity - A Phase 2 Trial. N Engl J Med. 2023;389:514-526. NEJM / PubMed
  • Jastreboff AM, et al. Tirzepatide Once Weekly for the Treatment of Obesity (SURMOUNT-1). N Engl J Med. 2022;387:205-216. PubMed
  • Frias JP, et al. Tirzepatide versus Semaglutide Once Weekly in Patients with Type 2 Diabetes (SURPASS-2). N Engl J Med. 2021;385:503-515. NEJM
  • Rosenstock J, et al. Efficacy and safety of the dual GIP and GLP-1 receptor agonist tirzepatide in type 2 diabetes (SURPASS-1). Lancet. 2021;398:143-155. The Lancet
  • Drugs.com drug references: retatrutide and tirzepatide