Tirzepatide is the dual GIP and GLP-1 agonist that beat semaglutide head-to-head in SURPASS-2 and SURMOUNT-5.

The short version

Tirzepatide is a once-weekly injectable medicine approved by the FDA for type 2 diabetes (May 2022) and for obesity and overweight (November 2023). It works by activating two gut hormone receptors at once — the GIP receptor and the GLP-1 receptor — which is different from older medicines in this class that only activate the GLP-1 receptor. Because it hits two targets, it tends to reduce blood sugar and body weight more than the earlier medicines. In the SURPASS-2 trial, it lowered blood sugar better than semaglutide in 1,879 people with type 2 diabetes over 40 weeks ^[3]. In the SURMOUNT-5 trial, it produced roughly 20% average body-weight loss versus 14% for semaglutide over 72 weeks in people with obesity but without diabetes ^[5]. The most common side effects are nausea, vomiting, and diarrhea — mostly during dose increases. This site is a plain-numbers reading desk for the published trial record. It is not a pharmacy, a clinic, or a vendor. What people report about Tirzepatide effects — including the downsides — is on the effects page.

What the Tirzepatide trial record shows

Tirzepatide (development code LY3298176) is a 39-amino-acid synthetic peptide — a tirzepatide peptide — derived from the GIP backbone, with a fatty-diacid arm attached via a linker to a lysine side chain ^[1]. That acyl modification gives it high albumin affinity and an approximately five-day half-life, which supports once-weekly subcutaneous dosing ^[13]. It was the first drug approved that simultaneously agonises both the glucose-dependent insulinotropic polypeptide (GIP) receptor and the glucagon-like peptide-1 (GLP-1) receptor — earning the informal label 'twincretin.'

In vitro signalling work showed tirzepatide engages the GIP receptor more fully than the GLP-1 receptor, and exhibits biased GLP-1 receptor signalling that favours the cAMP pathway over beta-arrestin recruitment ^[2]. That imbalance is proposed to contribute to its greater weight loss compared with selective GLP-1 receptor agonism alone ^[10].

The pivotal SURPASS-2 trial enrolled 1,879 adults with type 2 diabetes in an open-label 40-week head-to-head against semaglutide 1 mg once weekly ^[3]. Tirzepatide at 5, 10, and 15 mg reduced HbA1c (glycated haemoglobin — a marker of average blood glucose over three months) by 2.01, 2.24, and 2.30 percentage points, respectively, versus 1.86 percentage points with the comparator. All three tirzepatide doses were noninferior and superior. Body-weight reductions were also greater: differences of −1.9, −3.6, and −5.5 kg at the three doses ^[3].

For obesity without diabetes, SURMOUNT-1 enrolled 2,539 adults in a 72-week double-blind trial ^[4]. Average body-weight reductions at 5, 10, and 15 mg were −15.0%, −19.5%, and −20.9% versus −3.1% with placebo. More than 89% of participants receiving 15 mg achieved at least 5% weight loss; more than 56% achieved at least 20%.

For the direct head-to-head in obesity, tirzepatide vs semaglutide was measured in SURMOUNT-5: 751 adults with obesity but without type 2 diabetes, randomised to each drug's maximum tolerated dose for 72 weeks. Tirzepatide produced −20.2% versus −13.7% for the comparator — a statistically significant advantage of approximately 6.5 percentage points ^[5].

A propensity-matched retrospective cohort of 13,846 individuals with obesity (TriNetX database) found that tirzepatide was associated with a 27% lower risk of new-onset type 2 diabetes versus semaglutide (HR 0.73, 95% CI 0.58–0.92) and greater weight loss (−7.7 kg vs −4.8 kg). Among 8,446 people with pre-existing type 2 diabetes, tirzepatide was associated with a 46% lower risk of a composite cardiovascular outcome (HR 0.54, 95% CI 0.38–0.76) ^[8].

Tirzepatide mechanism of action

Incretin hormones (gut-derived hormones released after eating that amplify insulin secretion) normally circulate for only a few minutes. Tirzepatide mimics two of them simultaneously — GIP and GLP-1 — in a single 39-amino-acid molecule modified to stay active for days. Engaging both receptors amplifies glucose-dependent insulin secretion (insulin released only when blood glucose is elevated — not a flat on/off), suppresses glucagon (the pancreatic hormone that raises blood glucose), slows gastric emptying (reducing the speed at which the stomach passes food into the intestine), and suppresses appetite through both gut and central nervous system pathways ^[1][2].

A mechanistic review examining the GIPR (GIP receptor) specifically found that in the central nervous system, GIPR agonism attenuates nausea and independently suppresses appetite, while in adipose tissue it protects against ectopic fat deposition and improves insulin sensitivity — a pattern distinct from GLP-1R agonism and one that may explain why the combination consistently outperforms selective GLP-1 agonism for both glycaemia and weight ^[10].

The FDA approved tirzepatide for type 2 diabetes in May 2022, for chronic weight management in November 2023, and subsequently for moderate-to-severe obstructive sleep apnea in adults with obesity. A phase 3 trial (SUMMIT) demonstrated benefit in heart failure with preserved ejection fraction and obesity ^[15]; SYNERGY-NASH showed histological liver improvement in metabolic dysfunction-associated steatohepatitis (a progressive form of fatty liver disease) ^[16].

Tirzepatide results: key figures across the trial programme

The figures that define the tirzepatide results across the SURPASS and SURMOUNT programmes:

• HbA1c, type 2 diabetes (SURPASS-2, 40 weeks): −2.01 / −2.24 / −2.30 percentage points at 5/10/15 mg vs −1.86 for the comparator ^[3]
• Body weight, type 2 diabetes (SURPASS-2, 40 weeks): −7.8 / −10.3 / −12.4 kg at 5/10/15 mg vs −6.2 kg for the comparator ^[3]
• Body weight, obesity without diabetes (SURMOUNT-1, 72 weeks): −15.0% / −19.5% / −20.9% at 5/10/15 mg vs −3.1% placebo ^[4]
• Body weight, head-to-head in obesity (SURMOUNT-5, 72 weeks): −20.2% vs −13.7% for the comparator ^[5]
• HbA1c advantage over semaglutide (meta-analysis, 16 studies): mean difference −0.45 percentage points in favour of tirzepatide (95% CI −0.88 to −0.02; p=0.04) ^[9]
• Elimination half-life: approximately 5 days, consistent with once-weekly dosing ^[13]

For the full trial roster with methods, doses, and primary endpoints, see the Tirzepatide research page. For tirzepatide weight loss data specifically, the dedicated weight-loss page covers SURMOUNT-1, SURMOUNT-5, and the indirect evidence.

What this site is

Pharmacy Tirzepatide is an independent editorial project that indexes the peer-reviewed tirzepatide trial record. Despite the domain name, this is not a pharmacy. There are no products here, no prescriptions, and no sourcing information. Tirzepatide references link to the full citation list.

Every number on this site maps to a numbered citation. Quantitative claims without citations are not on this site. The negative-terms policy: no brand names appear anywhere on this site. The site uses only the INN name, tirzepatide.