Tirzepatide history: discovery to approval

Tirzepatide went from a laboratory compound to one of the most-studied prescription medicines in the world in about six years. The timeline below traces the key steps: the chemistry that made the dual-agonist idea feasible, the clinical milestones that validated it, and the regulatory decisions that put it into practice. This page is educational. It does not advise on starting, stopping, or sourcing tirzepatide; those conversations belong with a clinician.

The GIP receptor idea

For most of the 2000s, drug developers in the incretin field focused on GLP-1 receptor agonists. Glucagon-like peptide-1 drives insulin release, suppresses glucagon, and slows gastric emptying. The parallel gut hormone glucose-dependent insulinotropic polypeptide (GIP) was historically considered a less attractive target because GIP seemed to produce less weight loss on its own. Research groups including teams at Eli Lilly began asking whether stimulating both receptors simultaneously might amplify metabolic benefit over a pure GLP-1 approach like semaglutide. Animal models suggested the combination could produce greater reductions in body weight and blood glucose than either hormone alone.

2018: LY3298176 described and phase 2 trial published

In late 2018, two papers formally introduced the compound. Coskun and colleagues, writing in Molecular Metabolism, described LY3298176 (the internal development name for tirzepatide) as a 39-amino-acid peptide modified with a fatty diacid chain to extend its half-life to roughly five days and enable once-weekly dosing^[1]. Phase 1b data from 142 human subjects showed dose-dependent reductions in fasting glucose and body weight, with a gastrointestinal adverse-event profile consistent with the GLP-1 class.

Frias and colleagues published a randomised phase 2 trial in The Lancet the same year^[2]. Over 26 weeks in adults with type 2 diabetes, HbA1c fell by 1.06 to 1.94 percentage points across doses versus 0.06 on placebo. Weight losses ranged from 0.9 to 11.3 kg, with the highest doses outperforming dulaglutide, a GLP-1-only comparator. These two papers launched the phase 3 programme that would later become the branded product.

2021: the SURPASS programme

Phase 3 launched under the SURPASS trial name. SURPASS-1 (Rosenstock et al., Lancet 2021) tested tirzepatide monotherapy in adults with type 2 diabetes inadequately controlled on diet and exercise^[3]. All three doses produced HbA1c reductions of 1.87 to 2.07 percentage points versus a 0.04 percentage point increase on placebo, with weight reductions of 7.0 to 9.5 kg. SURPASS-2 (Frias et al., NEJM 2021) then ran tirzepatide against semaglutide 1 mg in 1,879 patients on metformin^[4]. Tirzepatide at 15 mg produced an HbA1c reduction of 2.30 percentage points versus 1.86 on semaglutide 1 mg, with an additional 5.5 kg weight reduction at the same dose.

May 2022: FDA approval as Mounjaro

In May 2022, the FDA approved tirzepatide as Mounjaro for adults with type 2 diabetes, making it the first dual GIP and GLP-1 receptor agonist approved anywhere in the world^[7]. The label carried a boxed warning: tirzepatide causes thyroid C-cell tumours in rats, with human relevance undetermined; personal or family history of medullary thyroid carcinoma and MEN-2 are contraindications. The EMA followed in September 2022, authorising Mounjaro centrally for the EU and EEA. NICE technology appraisal TA924 (October 2023) set the NHS access criteria for type 2 diabetes.

2022-2023: the SURMOUNT obesity programme

Alongside the diabetes trials, Eli Lilly ran the SURMOUNT obesity programme. SURMOUNT-1 (Jastreboff et al., NEJM 2022) enrolled 2,539 adults with obesity but without type 2 diabetes^[5]. At 72 weeks, mean body-weight reductions were 15.0%, 19.5%, and 20.9% on 5, 10, and 15 mg respectively, versus 3.1% on placebo. Over half the participants on 15 mg lost at least 20% of their body weight. SURMOUNT-2 (Garvey et al., Lancet 2023) extended the programme to adults with obesity and type 2 diabetes, reporting 12.8% and 14.7% reductions on 10 and 15 mg versus 3.2% on placebo^[6]. The safety pattern across both trials was consistent: predominantly gastrointestinal, dose-dependent, and concentrated during dose escalation.

November 2023 onward: Zepbound and new indications

In November 2023 the FDA approved tirzepatide as Zepbound for chronic weight management in adults with obesity or overweight plus a weight-related comorbidity. The same molecule at the same dose strengths, under a new US brand for insurance-formulary purposes. In December 2024 the Zepbound label expanded to moderate-to-severe obstructive sleep apnea in adults with obesity. In the EU and UK, the EMA and MHRA covered both the diabetes and weight-management indications under the single Mounjaro brand; NICE TA1026 (December 2024) set out the NHS obesity access criteria. SURMOUNT-5 (Aronne et al., NEJM 2025) then delivered a direct head-to-head result: a mean 20.2% body-weight reduction on tirzepatide against 13.7% on semaglutide 2.4 mg at 72 weeks, a 6.5-percentage-point difference.

Where things stand in mid-2026

Tirzepatide is a prescription medicine in the EU, EEA, UK, and US. The branded products are Mounjaro and, in the US, Zepbound. Grey-market vials labelled 'for research use only' do not carry the regulatory assurances of the licensed presentations. For per-country prescribing rules, see the tirzepatide regulation pages. Open questions include: cardiovascular-event reduction in obesity without diabetes, long-term safety over years of chronic use, and optimal management after discontinuation. For the full mechanism, safety profile, and trial map, see the tirzepatide peptide page.

This article is for educational and journalistic purposes. PeptideMethods Editorial Team does not hold medical credentials. Nothing here constitutes medical advice. Consult a clinician before making any decision about prescription medicines.