From Diabetes Treatment to Weight Management: The Story Behind Mounjaro and GLP-1 Medicines

Quick Answer

Mounjaro’s active ingredient, tirzepatide, grew out of more than a century of research into gut hormones called GIP and GLP-1. These hormones were first studied for type 2 diabetes and blood sugar control; their effect on appetite and weight was a secondary discovery, later confirmed in dedicated obesity trials.

Key Insights

• Research into gut hormones and appetite dates back to the early 1900s, long before ‘weight-loss drugs’ were a concept.
• GLP-1 was identified in 1986. Subsequent research established its role in reducing appetite and food intake, alongside its effects on blood glucose regulation.
• Tirzepatide was engineered to activate two hormone systems, GIP and GLP-1, at once, combining two earlier discoveries into one molecule.
• Mounjaro was first developed and approved for type 2 diabetes; its role in weight management was studied later, in dedicated trials.
• This history reflects a broader shift: obesity is now understood as a complex, biologically-influenced condition, not simply a lifestyle failure — which is also why treatment is never one-size-fits-all.

The science behind modern weight management medicines like Mounjaro did not start out as a weight-loss trend. It began more than a century ago, with scientists trying to answer a very different question: why does eating a meal trigger the body to release insulin, even before sugar from that meal has fully entered the bloodstream?

Understanding that backstory helps explain why doctors today talk about weight management as a medical issue rather than simply a matter of discipline, and why treatments like Mounjaro exist at all — as one option among several, suited to some people and not others.

Where Did GLP-1 Research Begin?

The story usually starts in the early 1900s, when physiologists noticed that a substance released by the gut seemed to send a message to the pancreas through the bloodstream — early evidence that the gut and pancreas were ‘talking’ to each other, as recounted in a historical review in Frontiers in Endocrinology (Holst, 2019). That single observation took decades to fully unpack.

By the 1960s, researchers had confirmed something that still surprises people today: eating a meal triggers more insulin release than delivering the same amount of sugar directly into the bloodstream. This became known as the ‘incretin effect’ — the gut’s ability to boost insulin release around mealtimes (Holst, 2019). The first hormone identified behind this was GIP. However, in people with type 2 diabetes, GIP’s insulin-stimulating effect is significantly reduced. This prompted researchers to investigate other incretin hormones, including GLP-1.

How Was GLP-1 Discovered?

In 1986, scientists identified GLP-1, a hormone involved in regulating blood glucose levels. Unlike GIP, GLP-1 retained its ability to stimulate insulin secretion in people with type 2 diabetes. Subsequent research also revealed its role in reducing appetite and food intake, an effect that would later become central to modern weight management medicines (Holst, 2019).

How Did GLP-1 Research Lead to Tirzepatide?

Natural GLP-1 breaks down in the body within minutes, limiting its usefulness as a treatment in its original form. Substantial research went into developing longer-acting GLP-1-based medicines for diabetes, including liraglutide, which is administered once daily, and semaglutide, which is available as a once-weekly injection (Knudsen and Lau, 2019).

Around the same time, scientists reconsidered GIP — the hormone that had originally seemed a dead end — with a hunch: could combining GIP and GLP-1 into a single molecule produce a stronger effect than either alone? This idea, described in Molecular Metabolism (Coskun et al., 2018), turned out to be right, and is how tirzepatide, the active ingredient in Mounjaro, came about. Our explainer on how Mounjaro works covers that dual mechanism in plain terms.

How Did Research Move From Diabetes to Weight Management?

Tirzepatide was first studied and approved to help control blood sugar in adults with type 2 diabetes, per the FDA-approved prescribing information (U.S. Food and Drug Administration, 2022). Because appetite effects kept appearing throughout decades of incretin research, scientists eventually ran dedicated trials specifically studying its effect on body weight in people with obesity, including the SURMOUNT-1 trial published in the New England Journal of Medicine (Jastreboff et al., 2022). This is a common pattern in medicine: many major weight management treatments were not originally invented as ‘diet drugs’ — they grew out of research into diabetes and metabolism, as traced in the Journal of Clinical Investigation (Drucker, 2024).

What This Means for You

This history explains why GLP-1-based treatments, including Mounjaro, remain prescription medicines: they emerged from, and are still governed by, the same rigorous clinical-trial and regulatory process as any other prescription drug — suitability is a doctor’s decision, not a self-assessment.

The research also shows why individual biology varies so much — which is exactly why dosage, treatment plans and results vary from person to person, and why not everyone will be a candidate for the same treatment.

None of this history makes any specific outcome guaranteed or effortless for an individual reader; it explains the science behind the option, not a promise about any one person’s results.

Medical science has changed how we understand weight management. Learn About ACC’s Doctor-Led Approach

Curious about the practical side of treatment? See our guide to how Mounjaro treatment is typically started. If a surgery-free, procedure-based option interests you more than medication, ACC also offers a gastric balloon programme as another doctor-led route → links to the general Weight Management service page.

Frequently Asked Questions

What was Mounjaro originally developed for?

Tirzepatide, the active ingredient in Mounjaro, was first studied and approved to help control blood sugar in adults with type 2 diabetes. Its effect on body weight was studied separately, in later trials (U.S. Food and Drug Administration, 2022; Jastreboff et al., 2022).

Is GLP-1 research new?

No. The GLP-1 hormone was identified in 1986, building on incretin research going back to the 1960s (Holst, 2019).

Are all GLP-1 medicines the same?

No. They differ in molecular structure, how long they stay active in the body, and, in tirzepatide’s case, whether they act on one hormone system or two (Kaneko, 2022).

Why is obesity now seen as a medical condition rather than a lifestyle issue?

Decades of hormone research show that appetite and weight regulation are governed by biological systems that vary considerably between individuals, which is exactly why medical assessment and supervision matter (Drucker, 2024).

Curious whether this history is relevant to your own situation? A doctor can help translate the research into what’s realistic for you — Explore Your Weight Management Options: GLP 1 & Gastric Balloon

Related Reading

• How Does Mounjaro Work for Weight Management?
• Mounjaro Dosage: How Is Treatment Typically Started?
• How Much Weight Can You Lose With Mounjaro?

References

Coskun, T., Sloop, K.W., Loghin, C. et al. (2018). LY3298176, a novel dual GIP and GLP-1 receptor agonist for the treatment of type 2 diabetes mellitus: From discovery to clinical proof of concept. Molecular Metabolism, 18, pp. 3–14. Available at: https://doi.org/10.1016/j.molmet.2018.09.009 (Accessed: 26 August 2026).

Drucker, D.J. (2024). The GLP-1 journey: from discovery science to therapeutic impact. Journal of Clinical Investigation, 134(2), e175634. Available at: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10786682/ (Accessed: 26 August 2026).

Holst, J.J. (2019). From the incretin concept and the discovery of GLP-1 to today’s diabetes therapy. Frontiers in Endocrinology, 10, article 260. Available at: https://pmc.ncbi.nlm.nih.gov/articles/PMC6497767/ (Accessed: 26 August 2026).

Jastreboff, A.M., Aronne, L.J., Ahmad, N.N. et al. (2022). Tirzepatide once weekly for the treatment of obesity. New England Journal of Medicine, 387(3), pp. 205–216. Available at: https://pubmed.ncbi.nlm.nih.gov/35658024/ (Accessed: 26 August 2026).

Kaneko, S. (2022). Tirzepatide: a novel, once-weekly dual GIP and GLP-1 receptor agonist for the treatment of type 2 diabetes. touchREVIEWS in Endocrinology, 18(1), p. 10. Available at: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9354517/ (Accessed: 26 August 2026).

Knudsen, L.B. and Lau, J. (2019). The discovery and development of liraglutide and semaglutide. Frontiers in Endocrinology, 10, article 155. Available at: https://pmc.ncbi.nlm.nih.gov/articles/PMC6474072/ (Accessed: 26 August 2026).

U.S. Food and Drug Administration (2022). MOUNJARO (tirzepatide) injection, for subcutaneous use: full prescribing information. Available at: https://www.accessdata.fda.gov/drugsatfda_docs/label/2022/215866s000lbl.pdf (Accessed: 26 August 2026).