Given once a week, Tirzepatide is a 39-amino-acid peptide, or short protein chain. It acts like GIP and GLP-1, two hormones made in your gut.
The first tests used cells and mice. The later trials show what changed in people.
What does Tirzepatide do?
Made in a lab, tirzepatide is a peptide, which means a short chain of 39 protein parts. This page explains how the weekly shot affects blood sugar, hunger, and weight. The drug acts like two hormones your gut makes after food; doctors call them GIP and GLP-1, and both help your pancreas put insulin into the blood while the sugar in your blood runs high. GLP-1 also slows the stomach and helps curb hunger. They also help your brain notice that you've eaten enough.
In May 2022, the FDA cleared tirzepatide for type 2 diabetes. Long-term weight care followed in November 2023. Adults with obesity and serious sleep apnea can also receive it. One Phase 3 trial, a large test done before approval, ran for 72 weeks. Average weight fell by as much as 20.9%. The medicine is given once a week just under the skin.
This page tells what happened in the main trials. The effects page explains possible gains and harms from Tirzepatide effects. Group averages can't predict your own blood sugar, sleep, weight, or stomach trouble. Age, health, food, and other drugs can change your result.
How can Tirzepatide act like two gut hormones?
In 2018, Coskun and his team first described tirzepatide as a 39-amino-acid peptide, or short protein chain, with a small fat piece that helps it cling to albumin in blood [1]. Tirzepatide then stays in the blood for about five days. That's why one shot can last a week [1].
In 2018, the first tests used cells in a dish and mice. Tirzepatide acted like GIP and GLP-1, two gut hormones that help after food. Mice ate less and lost more weight than mice given a drug that copied GLP-1 alone [1]. Mice can't tell us what a person will feel. A Phase 1 study, the first small human test, included 142 people. Their fasting blood sugar and weight fell more than with placebo, a shot with no tirzepatide [1].
Willard and his team tested the drug on cells in 2020 [2]. The cells responded more to GIP than to GLP-1. They also stayed ready to release insulin for longer. That may help explain why the cells released more insulin [2].
In 2021, Novikoff and his team watched living cells [4]. The parts that sense GLP-1 stayed on the outside of each cell. The cells also stayed ready to release insulin. These cell tests don't prove what happens in a person. The tirzepatide mechanism of action page explains more. Your result can't be read from a dish or a mouse. Those early findings gave the field a reason to run human trials.
What did large Tirzepatide trials called Phase 3 find?
In the 40-week SURPASS-2 trial, 1,879 adults with type 2 diabetes joined one of the large Phase 3 tests used before approval, and researchers compared tirzepatide with semaglutide 1 mg [3]. Weekly tirzepatide doses of 5, 10, and 15 mg lowered the three-month blood sugar result by 2.01, 2.24, and 2.30 points. Semaglutide lowered it by 1.86 points. All three tirzepatide groups had a larger drop [3]. They also lost 1.9, 3.6, and 5.5 kg more weight [3].
In the 72-week SURMOUNT-1 trial, 2,539 adults had obesity without diabetes. Some had a BMI, the doctor's height-and-weight measure, of 30 or more. Others began at 27 or more and had a health problem tied to weight. Weekly doses of 5, 10, and 15 mg cut average weight by 15.0%, 19.5%, and 20.9%. People given placebo, a shot with no tirzepatide, lost 3.1% [5]. Most stomach or bowel trouble was mild or moderate. It was worst while doses went up [5].
In 2025, SURMOUNT-5 followed 751 adults with obesity but no type 2 diabetes. They received tirzepatide at 10 or 15 mg. Others received semaglutide at 1.7 or 2.4 mg for 72 weeks. Average weight fell 20.2% with tirzepatide and 13.7% with semaglutide. The study found a clear difference [6]. More tirzepatide users also lost at least 10%, 15%, 20%, or 25% of their weight [6].
The Tirzepatide research page covers more trials. These averages can't tell you what your scale will show. Trial staff followed each person closely. Your health and care may differ from theirs.
How does Tirzepatide stay in your blood all week?
Natural GIP is a 42-amino-acid hormone. Natural GLP-1 has 30 amino acids, the small parts used to build proteins. The Tirzepatide peptide is a 39-amino-acid chain based on GIP [1]. Its shape lets one chain act like both hormones. A small fat piece keeps it in the blood for about five days. That supports one shot a week [1].
In 2024, Regmi and his team tested human fat cells in a dish. After food, when insulin was high, the drug helped cells take in sugar and fat. Between meals, when insulin was low, the cells released stored fat [8]. No people took part in this test. The finding may explain lower blood fats in human trials, but it doesn't prove the cause [8].
In 2025, Samms and his team reviewed past lab work [9]. They thought the action tied to GIP might lower hunger and nausea. They also thought GIP might help keep fat out of organs beyond what GLP-1 does. A review weighs work already done; it doesn't test new people. These ideas may explain human results, but they can't predict your response.
What else did Tirzepatide change in people?
In the 52-week SURMOUNT-OSA trial, adults had obesity and serious sleep apnea; breathing pauses fell by 25.3 an hour without a mask machine and by 29.3 an hour with one. Placebo cut about 5 pauses an hour [13]. This result led to FDA clearance for those adults.
In 2025, SUMMIT followed adults with obesity and heart failure. Their hearts could squeeze well but didn't fill as they should. Tirzepatide users had fewer bouts of worsening heart failure. They could also walk farther and handle daily tasks better than people given placebo [14].
In 2025, researchers reviewed several SURPASS trials. They counted 3,676 people for blood sugar and 4,121 for weight. A blood sugar drop of at least 20% by week 4 often came before better three-month blood sugar results. A weight drop of at least 5% by week 8 did too. People without those early drops still improved at every dose [10].
You can find each paper under Tirzepatide references. Your doctor can help match these group results to your health.