GLP-1 Resource Center

What is tirzepatide and how is it different from semaglutide?

Tirzepatide (Mounjaro, Zepbound) and semaglutide (Ozempic, Wegovy) are both GLP-1 class medications, but they work differently. Understanding the distinction explains why tirzepatide is associated with greater average weight loss, and why the nutritional consequences of both are similar despite the mechanistic difference.

Semaglutide: GLP-1 receptor agonist

Semaglutide mimics GLP-1 (glucagon-like peptide-1), a hormone produced in the gut after eating. It activates GLP-1 receptors in the pancreas (stimulating insulin secretion), in the gut (slowing gastric emptying), and in the brain (reducing appetite signals). The STEP 1 trial (Wilding et al., NEJM 2021) reported that semaglutide at 2.4mg weekly produced average weight loss of 14.9 percent of body weight over 68 weeks in people without diabetes.

Tirzepatide: dual GIP and GLP-1 receptor agonist

Tirzepatide activates two hormone receptors rather than one. In addition to GLP-1 receptors, it also activates GIP (glucose-dependent insulinotropic polypeptide) receptors. The dual activation has a more pronounced effect on appetite and insulin sensitivity than GLP-1 agonism alone. The SURMOUNT-1 trial (Jastreboff et al., NEJM 2022) reported that tirzepatide at 15mg weekly produced average weight loss of 22.5 percent of body weight. STEP 1 and SURMOUNT-1 are separate trials in different populations rather than a head-to-head comparison, so the difference between the two figures is indicative rather than exact.

Side effect profiles

Gastrointestinal side effects, nausea, constipation, vomiting, are common to both medications. In the STEP 1 trial, 44% of semaglutide patients reported nausea. In the SURMOUNT-1 trial, 31% of tirzepatide patients reported nausea at the 15mg dose. Hair shedding, sleep disruption, fatigue, and lean mass loss are reported with both medications as consequences of rapid caloric restriction rather than direct drug effects.

Lean mass: the difference most comparisons leave out

Across GLP-1 trials the share of weight lost as lean mass depends on the medication: about 26 percent on tirzepatide, and up to 45 percent on semaglutide, with a class-wide average near 30 percent and reported figures ranging from 20 to 50 percent.* The tirzepatide figure comes from the SURMOUNT-1 DXA substudy (Look et al., Diabetes, Obesity and Metabolism, 2025), which enrolled 255 participants and analysed 160, and reported 74 percent of the body weight reduction as fat mass and 26 percent as lean mass. The wider picture comes from a 2026 systematic review and meta-analysis in the International Journal of Obesity covering seven studies and 821 patients, which placed liraglutide at 14 to 22 percent, tirzepatide at about 26 percent and semaglutide at up to 45 percent.

Two pieces of context belong alongside those numbers. In SURMOUNT-1 the placebo group lost the same ratio, 25 percent against 26 percent, so this is weight loss behaving as weight loss rather than the medication doing something unusual. And fat-free mass measured by DXA includes water, glycogen and connective tissue, so it is not skeletal muscle alone. The 20 to 50 percent range seen across the literature is in line with what is reported after diet-induced weight loss and after bariatric surgery.

Read together, the two findings point in different directions. Tirzepatide is associated with more total weight loss (22.5 percent against 14.9 percent) and a lower share of that loss as lean mass. But these figures come from separate trials in different populations rather than head-to-head studies, the DXA substudies are small, and individual results vary considerably. None of it makes one medication the right one. Which medication suits you is a conversation with your prescriber, informed by your history, your other conditions and your bloodwork.

Why the nutritional consequences are similar

Both medications work primarily by reducing appetite and food intake. A 2025 joint advisory from four professional societies (Mozaffarian et al., Obesity) reported caloric intake reductions of 16 to 39 percent across the GLP-1 drug class. The resulting caloric restriction, and the micronutrient, protein, and electrolyte shortfall and digestive change that follow, is consistent across both.

The TAKE approach

TAKE Essentials are formulated for people on any GLP-1 class medication, semaglutide or tirzepatide, because the nutritional consequences are consistent regardless of which molecule drives the caloric restriction.* Which of them, if any, is worth taking is a question your bloodwork answers better than a website, and your clinician is the person to read it. View The Eight Essentials or start with the GLP-1 Resource Center.

These statements have not been evaluated by the Food and Drug Administration. TAKE products are not intended to diagnose, treat, cure, or prevent any disease. Individual results vary. Always speak with your healthcare provider about medication side effects or medical concerns.