How Does Tirzepatide Work? GIP and GLP-1, Animated
How does tirzepatide work? It copies two hormones your gut releases after a meal, GIP and GLP-1, and switches on the receptor for each one. Think of one key that opens two locks.
Tirzepatide is an approved prescription medicine in the US. It is sold as Mounjaro for type 2 diabetes and as Zepbound for weight management and sleep apnea. The animated video below tells the whole story in under 5 minutes.
How does tirzepatide work? Watch it animated
Tirzepatide: How Does It Actually Work? (Mounjaro, Zepbound), by Molecule Mechanics. 4:57, English captions, published 5 November 2026. Watch on YouTube.
Chapters
- 0:00What is tirzepatide (Mounjaro, Zepbound)?
- 0:14How does tirzepatide work?
- 0:37How does tirzepatide affect the pancreas, stomach and brain?
- 1:16What does tirzepatide share with lizard venom?
- 2:02Why does tirzepatide last for days?
- 2:22What did SURMOUNT-1 find?
- 2:44What are tirzepatide's side effects and boxed warning?
- 3:27Mounjaro vs Zepbound: what is each approved for?
- 4:12What does the lizard tail do?
- 4:28What did we learn about tirzepatide?
Read the video transcript+
Tirzepatide is one key that opens two locks in your body, and it's the prescription medicine inside Mounjaro and Zepbound. Part of it also matches something found in lizard venom, and by the end of this video you'll know why.
So how does it work? Your gut releases chemical messengers. Two of those messengers are called GIP and GLP-1, and each one is a key for its own lock. Tirzepatide fits both of those locks, which is why we call it one key for two locks. And here's a clue for later: the lizard's key fits the GLP-1 lock too.
The first place this matters is your pancreas, where tirzepatide helps it send out more insulin. It also turns down a signal that raises blood sugar, and both of these depend on how high your blood sugar is. The second place is your stomach, because tirzepatide slows how fast food leaves it, so your lunch takes the slow lane. The third place is your brain, where GLP-1 helps control appetite, and both locks sit in the parts that handle hunger. In animal studies, tirzepatide reaches those parts of the brain and switches on the nerve cells there. So one key works on two locks, and you see it in your pancreas, your stomach and your brain.
Now, about that lizard. In 1992, a veterans hospital lab in the Bronx was studying the venom of the Gila monster. Inside it they found a tiny chain of building blocks, and they named it exendin-4. Years later, a lab-made version of exendin-4, called exenatide, became the first approved drug to open the GLP-1 lock, for type 2 diabetes. Tirzepatide is a chain too, and the odd thing is that both chains end with the same tail. Your own two messengers don't have that tail, but tirzepatide isn't made from venom, because scientists started with human GIP. So what does that tail do? We'll come back to it at the end, after the big study and who this medicine is for.
First, though, why does tirzepatide last for days, when your own GLP-1 is half gone within minutes? Tirzepatide is half gone in about 5 days, and one reason is a small fatty part attached to it. That fatty part lets it ride on a protein in your blood, like a taxi, and the ride keeps it around longer.
Next comes the big study, which followed about 2500 adults for more than a year. Most had obesity, and none had diabetes. The tirzepatide group with the biggest average loss dropped about a fifth of their body weight, while the placebo group, who got a pretend medicine, lost about 3 percent. Those are averages, though, not promises.
So what's the catch? Many of the common side effects hit the gut, like nausea, diarrhea, vomiting and constipation. The label also lists serious risks, including an inflamed pancreas and gallbladder problems. There's a boxed warning too, about the thyroid, the small gland in the front of your neck. In rats, tirzepatide caused tumors there, and nobody knows yet whether it does that in people. That's why some people must not use it, including anyone who has had a rare thyroid cancer called medullary thyroid cancer, or whose family has had it. The same goes for anyone with a condition called MEN 2, or anyone seriously allergic to this medicine.
So who is it for? In the US it's prescription only, and it's meant to be used with diet and exercise. As Mounjaro, it's approved to help adults and children 10 and older with type 2 diabetes control their blood sugar. It's also approved to lower the risk of heart attack, stroke and heart-related death in adults with type 2 diabetes who are at high risk. As Zepbound, it's approved to help adults with obesity lose weight and keep it off, and overweight adults with a weight-related health problem too. Zepbound is also approved for moderate to severe sleep apnea in adults with obesity, which is when your breathing keeps pausing in your sleep. So it's the same key under two names, and each name is approved for different jobs.
Now, back to the lizard and that tail. Remember, the lizard's key fits the GLP-1 lock. Lilly, the company that makes tirzepatide, studied this tail in the lab, and they report it helps tirzepatide grip the GLP-1 lock. So that's tirzepatide: one long-lasting key for two locks, with a tail it shares with exendin-4, the molecule from lizard venom. Retatrutide is next. It's an experimental medicine in phase 3 studies, built to fit three locks, so why would anyone want a third?
Sources: The tirzepatide video and its description, YouTube; Molecule Mechanics channel, YouTube
Key facts
What it copies: GIP and GLP-1, two gut hormones known as incretins.
Where it acts: The pancreas (more insulin, less glucagon, both depending on how high blood sugar is), the stomach (food leaves more slowly) and the brain's appetite areas.
Why it lasts: A fatty side chain lets it ride on albumin in the blood. Half of it is cleared in about 5 days, not minutes.
Status: Approved and prescription only in the US, as Mounjaro and Zepbound.
Sources: Zepbound FDA label; Mounjaro FDA label; GIP and GLP-1 review, Journal of Diabetes Investigation 2010
How does tirzepatide work on GIP and GLP-1?
Tirzepatide works by switching on two receptors at once: the GIP receptor and the GLP-1 receptor. After you eat, your gut releases messengers called incretins. GIP comes from K cells in the upper small intestine. GLP-1 comes from L cells further down, in the lower intestine and colon. Each one has its own receptor, a lock that only the right key turns.
Tirzepatide is a chain of 39 amino acids, built on the sequence of human GIP; Peptides Vietnam's peptide reconstitution calculator covers the vial math for peptides like it. Its FDA label says it binds to and switches on both the GIP receptor and the GLP-1 receptor, the same targets the body's own hormones use. That is the one key, two locks idea.
It does not turn both locks equally. In lab tests by Lilly scientists, it held the GIP receptor about as tightly as natural GIP but held the GLP-1 receptor about 5 times more weakly than natural GLP-1. They describe it as imbalanced toward GIP.
Sources: GIP and GLP-1 review, Journal of Diabetes Investigation 2010; Tirzepatide structure study, PNAS 2022; Zepbound FDA label; Tirzepatide receptor binding study, JCI Insight 2020
What does tirzepatide do in the pancreas, stomach and brain?
Tirzepatide acts in three places: the pancreas, where insulin goes up and glucagon goes down; the stomach, where food leaves more slowly; and the brain areas that steer appetite.
Pancreas. Tirzepatide boosts the release of insulin and lowers glucagon, a hormone that raises blood sugar. The label says both effects are glucose-dependent, which means they depend on how high blood sugar is.
Stomach. It slows how fast food leaves the stomach. The label adds that this delay is largest at the start of treatment and fades over time.
Brain. GLP-1 helps regulate appetite and calorie intake. Receptors for both hormones sit in the brain areas that handle appetite, and in animal studies tirzepatide reaches those areas and switches on nerve cells there. On the GIP half, the label says only that nonclinical studies suggest it may add to the control of food intake.
Sources: Mounjaro FDA label; Zepbound FDA label; MedlinePlus, glucagon
Why does tirzepatide last for days?
Tirzepatide lasts for days because a fatty side chain lets it ride on albumin in the blood, and its design shields it from the enzyme that breaks down the body's own hormones. Your own GIP and GLP-1 are gone fast. An enzyme called DPP-4 breaks them down, and intact GIP and GLP-1 are half gone in about 5 minutes and about 2 minutes.
Tirzepatide is built to stay. The Mounjaro label gives an elimination half-life of about 5 days, and the Zepbound label gives about 5 to 6 days in people with overweight or obesity.
Two design choices help. A 20-carbon fatty acid chain lets it bind albumin, a protein made by the liver that travels in the blood, so it rides along like a passenger in a taxi. And an unusual amino acid called Aib sits at position 2, the spot DPP-4 normally recognizes and cuts.
Sources: GIP and GLP-1 review, Journal of Diabetes Investigation 2010; Mounjaro FDA label; Zepbound FDA label; Nauck and D'Alessio review, Cardiovascular Diabetology 2022; MedlinePlus, albumin
Is tirzepatide made from Gila monster venom?
No. Tirzepatide is not made from Gila monster venom: scientists started from the sequence of human GIP. But its last 10 amino acids match exendin-4, a peptide first found in that venom.
In 1992, a lab at the Veterans Affairs Medical Center in the Bronx, New York, isolated a peptide from the venom of the Gila monster, a lizard, and named it exendin-4. In 1993, another team showed that exendin-4 switches on the human GLP-1 receptor. A synthetic version, exenatide (Byetta), won FDA approval on 28 April 2005 as the first GLP-1 drug, for type 2 diabetes.
Tirzepatide ends with the same 10 amino acids that end exendin-4. Neither human GIP nor human GLP-1 has that tail. Lilly scientists report that this exendin-4 tail helps tirzepatide hold the GLP-1 receptor tightly.
| Peptide | Positions 30 to 39 | What it means |
|---|---|---|
| Tirzepatide | GPSSGAPPPS | Same tail as exendin-4 |
| Exendin-4 (Gila monster venom) | GPSSGAPPPS | Where the tail comes from |
| Human GIP | KGKKNDWKHN | Different |
| Human GLP-1 | None | The active hormone ends at position 30 or 31 |
Sources: Eng et al., Journal of Biological Chemistry 1992; Thorens et al., Diabetes 1993; GLP-1 drugs review, eClinicalMedicine 2024; Drugs@FDA, Byetta (NDA 021773); KEGG D11360, tirzepatide; UniProt P26349, exendin-4; UniProt P09681, human GIP; Tirzepatide structure study, PNAS 2022; Nauck and D'Alessio review, Cardiovascular Diabetology 2022
How is tirzepatide different from semaglutide?
Tirzepatide switches on two receptors, while semaglutide, the medicine in Ozempic, switches on one. Semaglutide's FDA label says it binds to and activates the GLP-1 receptor. Tirzepatide turns that lock and the GIP lock too. For the arithmetic behind each drug's vials, see the tirzepatide reconstitution calculator and the semaglutide reconstitution calculator.
The two were compared directly in SURMOUNT-5, a 72-week trial in 751 adults with obesity and without type 2 diabetes. Average weight change was -20.2% with tirzepatide and -13.7% with semaglutide. Those are averages across a group, not a promise for any one person.
Sources: Ozempic FDA label; Zepbound FDA label; SURMOUNT-5, New England Journal of Medicine 2025
What are Mounjaro and Zepbound approved for?
Mounjaro is approved for type 2 diabetes, and Zepbound for weight management and sleep apnea. Both brands are tirzepatide from Eli Lilly, sold under two names with different approvals. In the US both are prescription only and meant to be used with diet and exercise.
| Brand | First approved | Approved uses |
|---|---|---|
| Mounjaro | 13 May 2022 | Type 2 diabetes: helping blood sugar control in adults, and in children aged 10 and up. It is also approved to cut the risk of heart attack, stroke and cardiovascular death in high-risk adults with type 2 diabetes. |
| Zepbound | 8 November 2023 | Losing weight and keeping it off in adults with obesity, or with overweight and a weight-related health problem. Obstructive sleep apnea, moderate or severe, in adults who also have obesity, approved 20 December 2024. |
Sleep apnea is a disorder in which breathing stops or turns very shallow during sleep, again and again. For the wider GLP-1 picture where Peptides Vietnam is based, see our GLP-1 Vietnam guide.
Sources: Mounjaro FDA label; Zepbound FDA label; Drugs@FDA, Mounjaro (NDA 215866); Drugs@FDA, Zepbound (NDA 217806); FDA announcement, 20 December 2024; MedlinePlus, sleep apnea
What did the SURMOUNT-1 trial find?
In the SURMOUNT-1 trial, the tirzepatide group with the largest average loss lost 20.9% of body weight over 72 weeks, about a fifth, against 3.1% on placebo. The trial followed 2,539 adults with obesity, or with overweight and a weight-related complication, and none had diabetes. These are averages across a group, not a promise.
What are tirzepatide's side effects and boxed warning?
Tirzepatide's most common side effects hit the gut, and its labels carry a boxed warning about thyroid tumors seen in rats. The most common side effects on the Mounjaro label, seen in 5% or more of patients, are nausea, diarrhea, decreased appetite, vomiting, constipation, indigestion and stomach pain. The Zepbound list is similar and also includes tiredness, burping, hair loss and acid reflux. Serious risks on the labels include an inflamed pancreas and gallbladder disease. One less common report has its own write-up in our guide to Zepbound and vision changes.
Both labels carry a boxed warning about the thyroid, the small butterfly-shaped gland in the front of the neck. In rats, tirzepatide caused thyroid C-cell tumors, and it is unknown whether it does this in people. That is why the labels rule it out for anyone who has had medullary thyroid cancer or has it in the family, anyone with MEN 2, and anyone seriously allergic to tirzepatide.
Sources: Mounjaro FDA label; Zepbound FDA label; MedlinePlus, thyroid
What else do people ask about how tirzepatide works?
How does tirzepatide help with weight loss?+
Through appetite and digestion. GLP-1 helps regulate appetite and calorie intake, receptors for both GIP and GLP-1 sit in the brain areas that control appetite, and tirzepatide slows how fast food leaves the stomach. In the SURMOUNT-1 trial, the tirzepatide group with the largest average loss lost 20.9% of body weight over 72 weeks, against 3.1% on placebo. These figures describe the group and cannot predict one person's result.
Is tirzepatide made from animals?+
No. Scientists built tirzepatide on the sequence of human GIP, not from venom. Its last 10 amino acids do match the end of exendin-4, a peptide first isolated from Gila monster venom in 1992.
Is tirzepatide a peptide or a GLP-1?+
It is a peptide: a chain of 39 amino acids. It switches on the GLP-1 receptor and the GIP receptor, so researchers describe it as a dual GIP and GLP-1 receptor agonist rather than a GLP-1 drug alone.
What was Mounjaro originally approved for?+
Type 2 diabetes. The FDA first approved Mounjaro on 13 May 2022 to help adults with type 2 diabetes manage blood sugar. The same medicine was approved as Zepbound for weight management on 8 November 2023.
How long does tirzepatide stay in the body?+
The Mounjaro label gives an elimination half-life of about 5 days, which means half of it is cleared in about 5 days. The body's own GLP-1 is half broken down in about 2 minutes.
Sources: Zepbound FDA label; Mounjaro FDA label; SURMOUNT-1, New England Journal of Medicine 2022; Tirzepatide structure study, PNAS 2022; Nauck and D'Alessio review, Cardiovascular Diabetology 2022; Eng et al., Journal of Biological Chemistry 1992; Drugs@FDA, Mounjaro (NDA 215866); Drugs@FDA, Zepbound (NDA 217806); GIP and GLP-1 review, Journal of Diabetes Investigation 2010
What is Molecule Mechanics?
Molecule Mechanics is a YouTube channel of short, fully animated videos that explain how peptides and peptide drugs work. It covers what the research describes, how the mechanism works and the history behind it. It is education only and never tells anyone what to take or where to get it. Each video lists its primary sources, such as papers, regulators and trial registries, in its YouTube description.
The narration uses an AI voice made with ElevenLabs, and the animation is original. The tirzepatide video above is the channel's first, published on 5 November 2026. Peptides Vietnam hosts this page for the channel until it has a site of its own. How we check health facts is set out in our medical review policy, and how we fix mistakes in our corrections policy.
Next up is retatrutide, an experimental medicine built to fit three locks: the GIP, GLP-1 and glucagon receptors. It is not approved. ClinicalTrials.gov lists 14 phase 3 studies of it, and Drugs@FDA lists no approval. Retatrutide is also the subject of Peptides Vietnam's two most visited pages, the retatrutide calculator and the retatrutide reconstitution calculator.
Watch Molecule Mechanics on YouTube
Sources: The tirzepatide video and its description, YouTube; Molecule Mechanics channel, YouTube; Retatrutide phase 2 trial, New England Journal of Medicine 2023; ClinicalTrials.gov, retatrutide phase 3 studies
Education only, not medical advice. This page sets out what the FDA labels and published research say about how tirzepatide works. Any decision about a prescription medicine is one to make with a licensed clinician.