GIP Drugs for Weight Loss: Tirzepatide vs GLP-1 Explained

What makes tirzepatide a GIP drug?

The Zepbound and Mounjaro labels describe tirzepatide as an agonist at both the GIP and the GLP-1 receptor, and add that nonclinical studies suggest the added GIP activity may further contribute to regulation of food intake [1][2]. Semaglutide is a GLP-1 analogue with 94% sequence homology to human GLP-1 and a half-life of about one week; its label describes it as selectively binding to and activating the GLP-1 receptor [3].

GLP-1 itself is a hormone released by the intestine that helps lower blood glucose after eating and acts in parts of the brain that control appetite and food intake [7]. On the GIP side, the GIP receptor drives glucose-dependent insulin secretion when it is activated by GIP, and dual GIP plus GLP-1 agonism has become a treatment strategy for type 2 diabetes and obesity [8].

So the receptor-level difference is one receptor versus two, and both drugs delay gastric emptying [3][1].

Does tirzepatide beat semaglutide for weight loss?

On average, yes, in the head-to-head SURMOUNT-5 trial. SURMOUNT-5 was an open-label phase 3b trial that randomized 751 adults with obesity but without type 2 diabetes to the maximum tolerated dose of tirzepatide (10 or 15 mg) or semaglutide (1.7 or 2.4 mg) once weekly for 72 weeks. Mean weight change was -20.2% with tirzepatide and -13.7% with semaglutide (P<0.001), and waist circumference fell 18.4 cm versus 13.0 cm. Participants on tirzepatide were more likely to lose at least 10%, 15%, 20% and 25% of body weight [4].

The placebo-controlled trials that came before it set the original expectations. In SURMOUNT-1, 2,539 adults with obesity or overweight and no diabetes lost a mean 15.0%, 19.5% and 20.9% of body weight at 5, 10 and 15 mg of tirzepatide over 72 weeks, versus 3.1% on placebo [9]. In STEP 1, 1,961 adults lost a mean 14.9% on semaglutide 2.4 mg over 68 weeks versus 2.4% on placebo [10]. A direct comparison within one trial is more informative than comparing those two separate trials.

Two design details matter for reading the head-to-head result. It was open-label, so participants and investigators knew which drug was given, and each drug was dosed to the maximum each participant tolerated, so the result compares the best dose each person could reach rather than fixed doses [4].

Why the extra GIP activity might matter, and why that is unresolved

Whether GIP receptor activation explains the gap between the two drugs is not established by these trials [1][5][4]. The tirzepatide label credits GIP with a possible further contribution to food-intake regulation based on nonclinical (animal) work [1]; that has not been shown to account for the weight-loss difference in people.

Blood sugar: what the diabetes trial showed

SURPASS-2 randomized 1,879 adults with type 2 diabetes, open-label, to 40 weeks of tirzepatide 5, 10 or 15 mg or semaglutide 1 mg once weekly. HbA1c fell 2.01, 2.24 and 2.30 percentage points on the three tirzepatide doses versus 1.86 points on semaglutide, and body weight fell more with tirzepatide at all three doses [5]. Semaglutide 1 mg is a diabetes dose, not the 2.4 mg dose used for weight management [3][5].

Cardiovascular and other labeled differences

The Wegovy label includes reducing the risk of major adverse cardiovascular events in adults with established cardiovascular disease who have obesity or overweight, based on a trial of semaglutide 2.4 mg [3]. In SELECT, 17,604 adults with established cardiovascular disease and a BMI of 27 or higher but no diabetes were followed for a mean 39.8 months; cardiovascular death, nonfatal heart attack or nonfatal stroke occurred in 6.5% on semaglutide versus 8.0% on placebo (hazard ratio 0.80) [11]. Zepbound's labeled uses are weight management and sleep apnea [1].

Side effects: same class, different numbers

Gastrointestinal effects are the common class effect and are worst during dose escalation. In separate weight-management trials, nausea, vomiting, diarrhea and constipation were reported in 28%, 13%, 23% and 11% of people on Zepbound 15 mg versus 8%, 2%, 8% and 5% on placebo [1], and in 44%, 24%, 30% and 24% of people on Wegovy 2.4 mg versus 16%, 6%, 16% and 11% on placebo [3]. The labels note that rates across the trials cannot be directly compared [3].

Treatment stopped for adverse reactions in 6.7% on Zepbound 15 mg versus 3.4% on placebo, and in 6.8% on Wegovy 2.4 mg versus 3.2% on placebo [1][3]. Hair loss, which the labels link to weight reduction and which is more common in women, was reported by 4% to 5% on Zepbound versus 1% on placebo [1], and by 3% on Wegovy versus 1% [3]. Mean resting heart rate rose 1 to 3 beats per minute with tirzepatide and 1 to 4 beats per minute with Wegovy [1][3].

Both drugs carry a boxed warning for thyroid C-cell tumors seen in rodents, with human relevance unknown, and both are contraindicated in people with a personal or family history of medullary thyroid carcinoma or MEN 2 [3][1]. Both labels list acute pancreatitis, gallbladder disease, kidney injury from dehydration and serious hypersensitivity reactions among the warnings, and the Wegovy label says to discontinue if pancreatitis is suspected [3][1].

The Wegovy and Zepbound labels state that use with another GLP-1 receptor agonist is not recommended [3][1].

Birth control and other oral drugs

The tirzepatide label advises using a non-oral contraceptive method or adding a barrier method for 4 weeks after starting and after each dose increase [1]. Semaglutide labels carry no such advice, and a tablet interaction study found no clinically significant change in ethinyl estradiol or levonorgestrel with semaglutide [3]. Both drugs delay gastric emptying, and the Wegovy label advises increased monitoring of oral medicines with a narrow therapeutic index [3][1].

What happens when the drug is stopped

In STEP 4, 803 adults who had reached semaglutide 2.4 mg during a 20-week run-in were randomized to continue semaglutide or switch to placebo for 48 weeks. Those who continued lost a further 7.9% of body weight, while those switched to placebo gained 6.9% [12].

Where glucagon fits

Glucagon receptor agonism is a third target under study, not part of either approved drug. A 2026 computational design paper describes single-molecule peptides built to act at the GIP, GLP-1 and glucagon receptors, with changes intended to improve metabolic stability [6]. Tirzepatide is labeled as a GIP and GLP-1 receptor agonist and semaglutide as a selective GLP-1 receptor agonist [1][3].

How the two compare, by situation

For weight loss in adults with obesity and no diabetes, the direct comparison favors tirzepatide on group averages: 20.2% versus 13.7% at 72 weeks [4]. For type 2 diabetes, SURPASS-2 showed larger HbA1c reductions with tirzepatide at 40 weeks, though the semaglutide arm used 1 mg, a dose approved for diabetes rather than weight management [5][3]. For cardiovascular risk reduction, Wegovy injection and tablets have a labeled indication for eligible adults; SELECT tested the weekly 2.4 mg injection [3][11].