An evidence page. It summarises and grades the published record; it recommends nothing. The doses named below are those used in the trials and carried on the approved label, given as fact rather than advice.

01 Identity

Common name	Tirzepatide
Developmental code	LY3298176
Brand names	Mounjaro (type 2 diabetes); Zepbound (obesity, OSA)
Class	Synthetic peptide; dual agonist of the GIP and GLP-1 receptors (engineered from native GIP, fatty-diacid acylated)
Route	Once-weekly subcutaneous injection
Developer	Eli Lilly and Company
CAS number	2023788-19-2 · PubChem CID 163285896 · confirmed

A dual incretin agonist activating both GIP and GLP-1 receptors in one molecule, with GIP-receptor affinity close to native GIP and GLP-1 affinity roughly five-fold weaker than native GLP-1. It differs from retatrutide in lacking glucagon-receptor agonism.

02 Regulatory status

Tirzepatide is an approved prescription medicine, not an investigational or unlicensed compound. It holds marketing authorisation from the FDA, EMA, and MHRA among others — approved for type 2 diabetes (as Mounjaro, 2022), chronic weight management (as Zepbound, 2023), and moderate-to-severe obstructive sleep apnoea in adults with obesity.

It is prescription-only; supply or use outside a prescription is outside its licensed status. As an approved drug it carries an official prescribing label with defined indications, contraindications, and warnings (see §6), which take precedence over any third-party description.

03 Mechanism of action

GLP-1 receptor agonism drives the incretin effect, slows gastric emptying, and suppresses appetite centrally. Well-characterised drug-class mechanism.

GIP receptor agonism adds further incretin and appetite effects. This is the engineered piece that sets tirzepatide apart from GLP-1 mono-agonists such as semaglutide. Supported by comparative human trials.

The combined effect on glycaemic control and body weight is established in humans through large randomised trials, not merely inferred from mechanism.

04 Pharmacokinetics / pharmacodynamics

Terminal half-life of approximately 5 days, supporting once-weekly subcutaneous dosing, with steady state after about four weeks. Pharmacokinetics are characterised in humans through the registrational programme.

Treatment is initiated low and escalated stepwise to limit gastrointestinal effects; the maintenance doses studied and approved are 5, 10, and 15 mg weekly. Doses are stated as factual description of the trials and label, not as guidance.

05 Evidence by endpoint

The trial base here is unusually deep for this field: several large randomised programmes, run against active comparators and published in full.

5.1 — Glycaemic control in type 2 diabetes

The SURPASS programme (multiple large Phase 3 RCTs) produced HbA1c reductions of roughly 2.0–2.4 percentage points, with most participants reaching HbA1c below 7%, and was superior to placebo and to active comparators including semaglutide 1 mg, insulin degludec, and insulin glargine. Consistent and published in full.

Robust human

5.2 — Body-weight reduction in obesity / overweight

In SURMOUNT-1 (NEJM 2022; n=2,539; 72 weeks), mean weight reduction was about 16% (5 mg), 21.4% (10 mg), and 22.5% (15 mg) versus 2.4% on placebo. SURMOUNT-2/3/4 were concordant; SURMOUNT-5 (NEJM 2025), a head-to-head RCT, reported tirzepatide superior to semaglutide.

Robust human

5.3 — Obstructive sleep apnoea (with obesity)

The SURMOUNT-OSA trials reported reductions in the apnoea–hypopnoea index versus placebo, underpinning a regulatory approval for this indication.

Robust human

5.4 — Heart failure (HFpEF) and MASH

Dedicated trials (SUMMIT in HFpEF; SYNERGY-NASH in metabolic dysfunction-associated steatohepatitis) reported benefit on their respective endpoints. These are indication-specific evidence bases, and more recent.

Limited–robust human

5.5 — Cardiovascular outcomes

A dedicated cardiovascular outcomes trial (SURPASS-CVOT) is in progress. Cardiometabolic markers (blood pressure, lipids) improve consistently, but these are not event-reduction outcomes.

Mechanistic / no outcome data

06 Safety and adverse events

Unlike unapproved research compounds, tirzepatide has a characterised human safety profile from large trials and an official prescribing label.

Gastrointestinal events (nausea, vomiting, diarrhoea, constipation) are the most common — dose-dependent, usually mild-to-moderate, concentrated during escalation. Gallbladder events (e.g. cholecystitis) occur, consistent with substantial weight loss and the incretin class. Hypoglycaemia risk rises when combined with insulin or sulfonylureas. Acute pancreatitis, diabetic retinopathy complications, and acute kidney injury (with dehydration from GI losses) are label considerations.

Boxed warning (class): a risk of thyroid C-cell tumours seen in rodents underlies a contraindication in people with a personal or family history of medullary thyroid carcinoma or MEN 2. Human relevance is unestablished, but the contraindication stands. Not indicated for type 1 diabetes. The official label is the authoritative source for the full warning set; the above is a neutral summary.

07 Evidence summary

Endpoint	Grade
Glycaemic control (T2D)	Robust human
Weight loss (obesity)	Robust human
Obstructive sleep apnoea	Robust human
HFpEF / MASH	Limited–robust
Cardiovascular outcomes	No outcome data

08 References

Jastreboff AM, et al. Tirzepatide Once Weekly for the Treatment of Obesity (SURMOUNT-1). NEJM. 2022;387(3).DOI 10.1056/NEJMoa2206038 · NCT04184622
Tirzepatide after intensive lifestyle intervention (SURMOUNT-3). Nature Medicine. 2023.DOI 10.1038/s41591-023-02597-w
Aronne LJ, et al. Tirzepatide as Compared with Semaglutide for the Treatment of Obesity (SURMOUNT-5). NEJM. 2025;393(1).DOI 10.1056/NEJMoa2416394 · NCT05822830
SURPASS programme (SURPASS-1 to -5) — Phase 3 trials in type 2 diabetes, Lancet / NEJM / JAMA, 2021–2022.Add per-trial DOIs / NCT numbers
FDA prescribing information — Mounjaro (2022); Zepbound (2023, incl. OSA).Regulatory label; authoritative for indications and warnings