What the human research shows
The best-evidenced of the newer peptides: a full phase 3 programme in obesity and diabetes, a direct comparison against semaglutide, and an approval in sleep apnoea. The side-effect profile is the familiar GLP-1 one — gut symptoms during dose escalation — and it is well quantified.
Evidence profile0–5
- Metabolic & weightA5.0
- CardiovascularA1.7
- Muscle & growth—0.0
- Healing & repair—0.0
- Neuro & sleepA3.3
- Immune & inflammation—0.0
- Sexual & hormonal—0.0
- Skin & appearance—0.0
- Ageing & longevity—0.0
| Outcome | Grade | Effect size | Human studies | Where the evidence comes from |
|---|---|---|---|---|
| Body weight | AEstablished | Large | 10+ RCTs | SURMOUNT-1: −20.9% at 72 weeks on 15 mg vs −3.1% placebo in 2,539 adults. SURMOUNT-5 head-to-head: −20.2% vs −13.7% on semaglutide at 72 weeks.12 |
| Blood glucose (HbA1c) | AEstablished | Large | 5 SURPASS RCTs | SURPASS-2: HbA1c reductions of 2.0–2.3 points vs 1.9 on semaglutide 1 mg in type 2 diabetes.3 |
| Obstructive sleep apnoea | AEstablished | Moderate | 2 RCTs | SURMOUNT-OSA: apnoea–hypopnoea index fell by roughly 25–30 events per hour vs 5–6 on placebo; basis of the 2024 approval.4 |
| Cardiovascular events | AEstablished | Small | 1 large outcomes RCT (n=13,165) | SURPASS-CVOT, now published: tirzepatide was non-inferior to dulaglutide on major adverse cardiovascular events in type 2 diabetes. Superiority over an active GLP-1 comparator was not shown, and there is no placebo-controlled cardiovascular outcome trial. On this trial the FDA approved a cardiovascular risk-reduction indication on 28 August 2026; the grade and effect size do not change with the label.56 |
| GI side effectsadverse | AEstablished | Large | All trials | Nausea, diarrhoea and vomiting, mostly during dose escalation. In SURMOUNT-5, GI-related discontinuation was 2.7% vs 5.6% on semaglutide.12 |
Literature searched to 7 October 2026. Human studies only; animal and cell work informs the mechanism section and nothing else.
Registered trials
ClinicalTrials.gov lists 175+ interventional studies naming Tirzepatide as an intervention — 54 completed, 56 recruiting, and 32 with results posted to the registry.
A registration is not a result. Anyone can register a study, and many never report — so this list shows what has been attempted, not what has been shown. The graded evidence above is the answer to whether something works.
167 further studies are registered. Participant counts marked * are the sponsor's estimate, not a final enrolment. Source: ClinicalTrials.gov, read directly from the registry and refreshed weekly.
What it is
Tirzepatide is a 39-amino-acid peptide built on the GIP hormone backbone and modified so that it also activates the GLP-1 receptor and lasts about five days in the body. Eli Lilly launched it as Mounjaro for type 2 diabetes in 2022 and as Zepbound for weight management in 2023.
It is the drug that turned the semaglutide moment into a category: the first to show that adding a second gut-hormone receptor produces meaningfully more weight loss, and the first to be tested against semaglutide directly rather than by cross-trial comparison.
How it is thought to work
Like semaglutide it activates GLP-1 receptors — more insulin when glucose is high, slower stomach emptying, less appetite. The GIP component appears to add to the appetite effect and to improve how the body handles fat and insulin, and may temper nausea somewhat; the mechanism of that second part is still being worked out.
What is still unknown
- Whether the cardiovascular benefit matches or exceeds semaglutide's; the outcomes trial used dulaglutide, not placebo, as comparator.
- Weight regain after stopping — the withdrawal study (SURMOUNT-4) shows substantial regain, as with semaglutide.
- Long-term effects of the lean-mass component of weight loss.
The molecule and how long it lasts
- Formula
- C225H348N48O68
- Molecular weight
- 4813 g/mol
- CAS number
- 2023788-19-2
- PubChem
- CID 166567236
PubChem record, read 23 September 2026.
- Route
- Subcutaneous injection, once weekly
- Half-life
- About 5-6 days
- Licensed regimen (Zepbound)
- 2.5 mg weekly for 4 weeks, then increase in 2.5 mg increments after at least 4 weeks on current dose; maintenance 5, 10 or 15 mg weekly (10 or 15 mg for OSA); maximum 15 mg weekly
From the approved product's prescribing information: Zepbound prescribing information (DailyMed) The regimen is the label's own wording, reproduced as a regulatory fact.
Regulatory status
Mounjaro authorised via the EMA (2022; weight management added 2023). Grey-market versions are unlicensed medicines.
Mounjaro and Zepbound. On 28 August 2026 the FDA added an indication for Mounjaro to lower the risk of major adverse cardiovascular events in adults with type 2 diabetes at high risk, on the SURPASS-CVOT trial. The shortage was declared resolved in December 2024; compounding enforcement discretion has ended. More than 730 adverse-event reports for compounded versions by May 2026.
Mounjaro licensed by the MHRA. Counterfeit Zepbound/Mounjaro pens were among the products seized from illicit UK manufacturing sites in 2025–2026.
Mounjaro on the ARTG, prescription-only. Compounded tirzepatide has been unlawful since 1 October 2024.
Mounjaro and Zepbound carry a DIN. Vials sold online as tirzepatide were among the products Health Canada seized in August 2025.
Not on the 2026 Prohibited List, and WADA confirmed on 21 September 2026 that GLP-1 receptor agonists stay off the 2027 List. Tirzepatide remains on WADA's Monitoring Program.
Questions people actually ask
Is tirzepatide better than semaglutide for weight loss?
Is tirzepatide a peptide?
What are the main side effects?
Does the weight come back after stopping?
One page per claimed effect
- ADoes Tirzepatide help with body weight?10+ RCTs
- ADoes Tirzepatide help with blood glucose?5 SURPASS RCTs
- ADoes Tirzepatide help with obstructive sleep apnoea?2 RCTs
- ADoes Tirzepatide help with cardiovascular events?1 large outcomes RCT (n=13,165)
- AHow common is GI side effects with Tirzepatide?All trials
References
- 1Jastreboff AM, et al. Tirzepatide once weekly for the treatment of obesity (SURMOUNT-1).N Engl J Med, 2022;387:205–2162,539 adults; −20.9% at 72 weeks on 15 mg.
- 2Aronne LJ, Horn DB, le Roux CW, et al. Tirzepatide as compared with semaglutide for the treatment of obesity (SURMOUNT-5).N Engl J Med, 2025;393(1):26–36751 adults, 72 weeks; −20.2% vs −13.7%; waist −18.4 cm vs −13.0 cm.
- 3Frías JP, et al. Tirzepatide versus semaglutide once weekly in patients with type 2 diabetes (SURPASS-2).N Engl J Med, 2021;385:503–5151,879 adults; HbA1c and weight vs semaglutide 1 mg.
- 4Malhotra A, et al. Tirzepatide for the treatment of obstructive sleep apnea and obesity (SURMOUNT-OSA).N Engl J Med, 2024;391:1193–1205Two trials, 469 adults; basis of the sleep-apnoea approval.
- 5Nicholls SJ, et al. Cardiovascular outcomes with tirzepatide versus dulaglutide in type 2 diabetes (SURPASS-CVOT).N Engl J Med, 202513,165 analysed; non-inferior to dulaglutide, superiority not shown.
- 6Eli Lilly. FDA approves Lilly's Mounjaro (tirzepatide) to reduce cardiovascular risk in adults with type 2 diabetes.Press release, 28 Aug 2026Indication based on SURPASS-CVOT (13,299 randomised; hazard ratio 0.92, 95.3% CI 0.83–1.01 vs dulaglutide).
Change log
- 2026-10-07WADA's 2027 List status (published 21 Sep 2026) added to the sport row. No change to the evidence or grades.
- 2026-09-23US cardiovascular risk-reduction indication (28 Aug 2026) added to the answer and the US status row. Grades unchanged: the approval rests on the non-inferiority trial already cited.
- 2026-09-02Full page. Added HbA1c, sleep-apnoea and cardiovascular rows; SURMOUNT-5 head-to-head figures; FAQ and regional status.
- 2026-09-01Initial publication.