TZ-2 (Tirzepatide-Type) Dual GIP/GLP-1 Agonist: A Research Overview

TZ-2 is our catalog name for a tirzepatide-type peptide, a single molecule with agonist activity at both incretin receptors: the glucose-dependent insulinotropic polypeptide receptor (GIPR) and the glucagon-like peptide-1 receptor (GLP-1R). In the literature the compound is tirzepatide, first described under the development code LY3298176 [2]. It was the first monomeric peptide with dual activity at both incretin receptors to reach clinical use [7], and it is approved as a prescription medicine under the brand names Mounjaro and Zepbound. TZ-2 is neither of those products. It is research material, and throughout this overview TZ-2 refers to our material while tirzepatide refers to the compound as studied in the cited papers.

The Two Incretin Receptors

Incretins are gut peptides secreted after nutrient intake that stimulate insulin secretion together with elevated glucose. GIP comes from K cells in the upper gut and GLP-1 from L cells in the lower gut, and together they account for the incretin effect: a two- to threefold larger insulin response to oral than to intravenous glucose [3]. Both hormones are rapidly degraded by the enzyme dipeptidyl peptidase-4, which drove the development of degradation-resistant analogues [9].

GIP and its receptor

Postprandial GIP levels are roughly fourfold higher than GLP-1, and GIP accounts for most of the insulinotropic incretin effect in humans [2]. Beyond the islet, GIP acts on adipose tissue, where it promotes energy storage, and on bone [9]. GIP was long regarded as the less promising incretin target: its insulinotropic effectiveness is substantially reduced in type 2 diabetes [3], and the implications of its lipogenic actions in fat are still debated [8].

GLP-1 and its receptor

GLP-1R activation produces glucose-dependent insulin secretion, glucose-dependent inhibition of glucagon release, slower gastric emptying and satiety [9]. Unlike GIP's, GLP-1's insulinotropic and glucagon-suppressing effects are preserved in type 2 diabetes, which is why GLP-1 became the parent compound of incretin-based pharmacology [3].

Why Combine Them in One Molecule

Selective GLP-1R agonists are limited by dose-related gastrointestinal effects, so one line of research asked whether engaging a second pathway could widen the useful range [8]. The approach taken was to engineer GLP-1 activity into the sequence of GIP. As one review puts it, GIP's ability to improve lipid and glucose metabolism is most evident when paired with the appetite-reducing mechanism of GLP-1 [8].

The tirzepatide discovery paper framed the question directly: does GIP's metabolic action add to selective GLP-1R agonism [2]? In mice, tirzepatide decreased body weight and food intake significantly more than a GLP-1R agonist. It also improved glucose tolerance in both GIPR-knockout and GLP-1R-knockout mice, and in wild-type mice given a GLP-1R antagonist, showing that it acts through each receptor independently [2].

Structure and Acylation

Tirzepatide is a 39-amino-acid linear peptide built on a GIP-based sequence. It contains two non-coded α-aminoisobutyric acid (Aib) residues, at positions 2 and 13, and an amidated C-terminus, and it carries a C20 fatty diacid attached through a linker to the lysine at position 20 [2]. The acylation enables albumin binding, and in the phase 1 program the mean half-life was approximately 5 days, long enough that the clinical studies used once-weekly administration [2].

In receptor binding studies, tirzepatide bound GIPR with an affinity comparable to native GIP and GLP-1R with an affinity about fivefold weaker than native GLP-1. In cAMP assays in HEK293 cells, its potency was similar to GIP at GIPR and about 13-fold weaker than GLP-1 at GLP-1R [2].

Imbalanced and Biased Agonism

Those numbers are the starting point for a 2020 pharmacology study that describes tirzepatide as an imbalanced and biased dual agonist [4]. Imbalanced refers to receptor occupancy: the authors developed a method for estimating occupancy of each receptor at clinically effective exposures and found greater engagement of GIPR than of GLP-1R. Biased refers to signaling: at GIPR tirzepatide mimics native GIP, but at GLP-1R it favors cAMP generation over β-arrestin recruitment and drives receptor internalization less strongly than GLP-1 [4].

The paper also linked the bias to function. In primary islets, β-arrestin1 limited the insulin response to GLP-1 but not to GIP or tirzepatide, which the authors interpreted as evidence that the biased GLP-1R agonism enhances insulin secretion [4]. For experimental design, the lesson is that dual agonist does not mean equal agonist. A readout in a GLP-1R system reflects partial, pathway-selective engagement, so measuring cAMP alone can miss what distinguishes the compound from GLP-1.

What the Published Clinical Trials Report

Tirzepatide has a large controlled-trial literature. The three trials below cover its main comparisons: against placebo, against a selective GLP-1R agonist, and in obesity without diabetes. Each figure is a finding of that trial in its study population, using the pharmaceutical product under medical supervision.

SURPASS-1: tirzepatide versus placebo in type 2 diabetes

This 40-week, double-blind trial randomized 478 adults with type 2 diabetes not controlled by diet and exercise alone to one of three tirzepatide dose levels or placebo [5]. HbA1c fell by 1.87 to 2.07 percentage points across the tirzepatide groups, versus a rise of 0.04 with placebo. The most frequent adverse events were mild to moderate, transient gastrointestinal events, and no clinically significant or severe hypoglycaemia was reported with tirzepatide [5].

SURPASS-2: tirzepatide versus semaglutide

This open-label, 40-week trial randomized 1,879 people with type 2 diabetes to one of three tirzepatide dose levels or the selective GLP-1R agonist semaglutide [1]. HbA1c changed by -2.01 to -2.30 percentage points with tirzepatide versus -1.86 with semaglutide; every tirzepatide group was noninferior and superior to the comparator. Body-weight reductions were also greater with tirzepatide, with estimated between-group differences of -1.9 to -5.5 kg [1].

SURMOUNT-1: tirzepatide in obesity without diabetes

This 72-week, double-blind trial randomized 2,539 adults with obesity, or with overweight plus a weight-related complication, and no diabetes, to one of three tirzepatide dose levels or placebo [6]. Mean body-weight change at week 72 was -15.0%, -19.5% and -20.9% across the tirzepatide groups, versus -3.1% with placebo. A reduction of 20% or more occurred in 50% and 57% of participants in the two higher-dose groups, versus 3% with placebo. Adverse events were mostly gastrointestinal, mild to moderate, and concentrated in the escalation period [6].

Dual Versus Triple Agonism

TZ-2 and RT-3 (our retatrutide-type material) belong to the same design lineage: tirzepatide and retatrutide are both GIP-derived peptides carrying a fatty diacid on a lysine side chain [2, 11]. The difference is the glucagon receptor. A dual GIPR/GLP-1R agonist acts mainly on food intake, insulin secretion and glucagon suppression. A triple agonist adds glucagon receptor activity, which in obese mice augmented body-weight loss by raising energy expenditure on top of the intake reduction driven by the two incretin receptors [10].

That makes the pair a natural comparison in the laboratory, with one caution. The two molecules also differ in their potency at GIPR and GLP-1R, so a head-to-head result is not a clean test of glucagon receptor activity alone. Receptor-selective antagonists or knockout systems are needed to attribute a difference to one receptor. Our RT-3 research overview covers the glucagon side in detail.

Open Research Questions

• The GIP question: GIP's insulinotropic effect is blunted in type 2 diabetes [3] and its role in adipose tissue is debated [8], yet GIPR is the receptor tirzepatide engages most [4]. Which GIPR-expressing tissues carry the additional effect over GLP-1R agonism is not settled.
• Imbalance versus exposure: how much of the clinical profile follows from GIPR-weighted occupancy and GLP-1R bias [4], rather than from total exposure, remains to be separated experimentally.
• Species translation: the occupancy and bias work used human receptor pharmacology [4]. Rodent studies should confirm the potency and bias profile at the receptors of the species actually used.
• Where multi-agonists go next: reviews of the field regard tirzepatide as the first step in a broader programme of multi-receptor peptides rather than an end point [7].

Laboratory Handling and Storage

TZ-2 is supplied as a white lyophilized powder with a specified storage temperature of -20°C.

• Keep lyophilized material sealed at -20°C away from light and moisture, and let the vial equilibrate to room temperature before opening.
• Reconstitute in a solvent that suits the assay (the specification lists sterile water) and prepare single-use aliquots rather than freezing and thawing one stock repeatedly. Record lot, concentration, solvent and date on each.
• Decide how albumin will be handled before running potency assays. Because the C20 diacid binds albumin, serum or BSA shifts apparent potency. The discovery work ran its in-vitro binding and cAMP assays without albumin so tirzepatide could be compared directly with native GIP and GLP-1 [2].
• Use native GIP and GLP-1 as reference ligands, and where receptor attribution matters, knockout cells or selective antagonists, as the discovery paper did in mice [2].
• To capture bias, pair cAMP readouts with β-arrestin recruitment or internalization assays at GLP-1R [4].

Every batch of TZ-2 is independently third-party tested. The certificate for lot TZ20001 (20mg, 99.76% purity, tested August 2026) is published on our COA page. TZ-2 does not ship with a printed certificate; the published certificate is the record.