# Semaglutide vs Tirzepatide: Head-to-Head Research | Digest > Semaglutide vs tirzepatide, head-to-head: SURMOUNT-5 weight loss -13.7% vs -20.2% and SURPASS-2 in diabetes. But semaglutide owns the outcome trials — SELECT, SUSTAIN-6, FLOW. Cited. One drug wins the scale, the other owns the outcome trials. Both statements are backed by published numbers. ## The short version Here is **semaglutide vs tirzepatide** in two lines. On weight, tirzepatide wins the only large head-to-head trial: about 20% lost versus 14% over 72 weeks [1]. On proven outcomes — heart attacks, strokes, kidney failure prevented — semaglutide has the deeper published record [3][5]. Both are once-weekly injections that act on the GLP-1 system. The difference is that tirzepatide also activates a second hormone receptor (GIP), which appears to give it an edge on weight and blood sugar. But "more weight lost" and "more events prevented in a hard-endpoint trial" are different claims, and right now they point at different drugs. This page lays out every comparable figure so you can see the trade clearly. It is a reading of the trial record, not advice, and it names no brands — only the generic compounds. ## Weight: SURMOUNT-5, the direct comparison The cleanest comparison is **SURMOUNT-5**, a 2025 head-to-head trial that randomized 751 adults with obesity to semaglutide or tirzepatide for 72 weeks. The result: a mean weight change of -20.2% with tirzepatide versus -13.7% with semaglutide — roughly a 6.5 percentage-point advantage for tirzepatide, statistically significant at P<0.001 [1]. That is a direct, randomized comparison, which is the strongest kind of evidence for a head-to-head question. It does not depend on comparing across separate trials with different populations. On the specific endpoint of mean body-weight reduction in adults with obesity, tirzepatide produced the larger number. ## Diabetes and blood sugar: SURPASS-2 The pattern repeated in type 2 diabetes a year earlier. In **SURPASS-2**, the dual GIP/GLP-1 agonist tirzepatide produced greater reductions in both HbA1c (a three-month blood-sugar average) and body weight than once-weekly semaglutide 1.0 mg at 40 weeks [9]. For context on semaglutide's own diabetes performance against an older GLP-1 drug: in SUSTAIN 7, semaglutide produced greater HbA1c and weight reductions than once-weekly dulaglutide [13]. So the within-class hierarchy that emerges is consistent — tirzepatide ahead of semaglutide, semaglutide ahead of dulaglutide — though each comparison rests on its own trial. One caution about reading head-to-head numbers across these studies: the semaglutide dose differs by trial. SURPASS-2 compared tirzepatide against the 1.0 mg diabetes dose of semaglutide [9], while SURMOUNT-5 used the higher 2.4 mg obesity dose [1]. That matters because semaglutide's effect is dose-dependent, so the size of tirzepatide's lead is not a single fixed gap — it depends on which semaglutide dose sits on the other side of the comparison. The direction of the result is consistent; the magnitude is contextual. ## Where semaglutide leads: hard-endpoint outcomes Weight and HbA1c are surrogate measures. The endpoints that change lives are events — heart attacks, strokes, kidney failure, death — and here semaglutide has the published depth. **SELECT** (n=17,604) showed a 20% reduction in major adverse cardiovascular events in people with cardiovascular disease and obesity but no diabetes (HR 0.80; 95% CI 0.72-0.90; P<0.001) [3]. **SUSTAIN-6** showed a 26% reduction in the same composite in type 2 diabetes (HR 0.74; 95% CI 0.58-0.95) [4]. **FLOW** (n=3,533) showed a 24% reduction in major kidney events (HR 0.76; 95% CI 0.66-0.88) [5]. Tirzepatide's dedicated cardiovascular-outcome trial had not reported equivalent published hard-endpoint results at the time of this corpus. A 2025 modelling study projected 10-year cardiovascular-risk differences between the two agents [10], but a projection is not an outcome trial. So the honest scorecard: tirzepatide leads on the scale and on HbA1c; semaglutide leads on the breadth of proven outcomes. ## Why the mechanisms differ The reason the two drugs produce different numbers traces to what they bind. Semaglutide is a single-receptor agonist: it activates only the GLP-1 receptor, the same target as the natural incretin hormone GLP-1 [27]. Its weight effect runs mainly through appetite circuits in the brain — rodent work showed it reaches the brainstem, area postrema and hypothalamic arcuate nucleus to reduce food intake without lowering energy expenditure [6]. Tirzepatide adds a second arm: it activates the GIP receptor as well as GLP-1 (a "dual agonist"). GIP is a second incretin hormone, and engaging both pathways appears to be the mechanistic basis for the larger weight and HbA1c effects seen in the direct comparisons [1][9]. Semaglutide's counter-argument is breadth of proof rather than peak effect: its single-receptor mechanism has been carried all the way through to hard cardiovascular and kidney endpoints in SELECT, SUSTAIN-6 and FLOW [3][4][5], and to a histologic liver benefit in the 2025 ESSENCE trial [8]. Different molecular design, different shape of evidence. ## How to read the trade-off The two questions a comparison usually collapses into — "which loses more weight?" and "which is better?" — do not have the same answer here. SURMOUNT-5 settles the first in tirzepatide's favor [1]. The second depends on what you weight most: maximal weight loss, where the evidence favors tirzepatide, or the longest and broadest record of preventing cardiovascular and kidney events, where it favors semaglutide [3][5]. This digest does not adjudicate that choice — that is a clinical decision, and there is no clinician here. It lays out the figures and cites each one. For the weight evidence in depth, see [semaglutide weight loss](/weight-loss); for the mechanism behind the GIP/GLP-1 difference, see the [Semaglutide research](/research) page. --- A data-forward reading of the semaglutide trial ledger, posted head-to-head against tirzepatide — every figure reconciled to its study, with no clinic at the desk and nothing here dosed or sold.