Mounjaro's peptide name: what tirzepatide actually is

What exactly does the peptide name tirzepatide mean?

A peptide is a chain of amino acids (the building blocks of proteins) short enough to be described precisely at the molecular level. Tirzepatide is a synthetic peptide: it was designed in a laboratory to mimic two naturally occurring gut hormones rather than derived from any plant or animal source.

The name itself follows International Nonproprietary Name (INN) conventions. The suffix -tide marks it as a peptide-class drug; the stem -glutide signals a GLP-1 receptor agonist, while the prefix encodes the additional GIP action. If you have seen the name in a clinical trial paper or on the BNF's tirzepatide monograph, it is always tirzepatide, the brand Mounjaro appears only in product-specific contexts.

One misconception worth gently clearing up: some people assume Mounjaro and tirzepatide are different products. They are not. Every Mounjaro KwikPen delivered to a patient in the UK contains tirzepatide as its active substance. The peptide name is simply what clinicians, regulators and researchers use when the conversation is about the molecule rather than the commercial product.

You can read more about the relationship between the two names on our guide to Mounjaro's names and what they mean.

How does tirzepatide's dual-receptor action compare with other peptide medicines for weight loss?

Before tirzepatide, licensed injectable weight-loss medicines in the UK targeted one receptor: the GLP-1 receptor. Semaglutide (sold as Wegovy) is a GLP-1 receptor agonist, a single-pathway peptide. Tirzepatide is a GIP and GLP-1 receptor co-agonist, activating both pathways with a single weekly injection.

GLP-1 slows gastric emptying and signals satiety to the brain. GIP complements this through separate but overlapping mechanisms that influence energy balance and fat metabolism. Activating both appears to produce a greater appetite-reducing effect than GLP-1 alone, which is reflected in the clinical trial data reviewed by NICE in TA1026: in the SURMOUNT-1 trial, participants taking tirzepatide 15 mg lost around 20–21% of body weight on average over 72 weeks. The SURMOUNT-5 head-to-head trial, published in the New England Journal of Medicine in 2025, found tirzepatide produced greater average weight loss than semaglutide 2.4 mg over the same period.

This dual-peptide mechanism is also why tirzepatide is the only medicine of its kind in the UK. No other licensed weight-loss medicine shares this design. For a deeper look at what this means in practice, the GLP-1 peptide and tirzepatide page covers the receptor science in plain language.

Does the peptide name change anything about how Mounjaro is prescribed or regulated?

In clinical and regulatory settings, tirzepatide is always the name that carries the legal weight. The MHRA licensed tirzepatide for weight management in the UK. NICE's recommendation covers tirzepatide. The prescriber writes tirzepatide on a private prescription; the pharmacy dispenses Mounjaro. The patient receives Mounjaro. All of these refer to the same molecule.

Knowing the peptide name matters practically for one main reason: when you see tirzepatide in a leaflet, a trial summary or a clinical letter, you can be confident it refers to Mounjaro. Conversely, if you encounter a product marketed under a different brand name for the same molecule (for instance, Zepbound, which is the US brand name for tirzepatide and does not exist as a UK-licensed product) the peptide name confirms whether the active substance is the same one licensed here.

If you are curious whether tirzepatide and Mounjaro are truly interchangeable descriptions, this page works through the differences and similarities in more detail. For context on what private treatment costs in the UK, our Mounjaro prices guide explains what a legitimate private prescription typically includes. Eligibility is always assessed by a prescriber, BMI, health history and individual circumstances all factor into whether tirzepatide is appropriate for a given person.

At nume, every consultation is read by a GPhC-registered Independent Prescriber on the day it arrives. A real clinician considers your answers; no automated system makes the call. If you would like to explore whether tirzepatide might be right for you, you are welcome to check your eligibility with a free consultation, and our guide to the Mounjaro booster explains how some people use an additional support step alongside their treatment.