SURMOUNT-5 explained: tirzepatide vs semaglutide head to head

The short answer: SURMOUNT-5 is the first randomized trial to put tirzepatide and semaglutide head to head for obesity, and tirzepatide won on the primary endpoint by about 6.5 percentage points of body weight at 72 weeks. [1] It answers the "which one loses more weight" question for people without diabetes. It does not answer questions about heart outcomes, long-term safety, or which drug a given person should use.

This breakdown covers what the study shows. It does not give dosing advice.

The design

SURMOUNT-5 was a phase 3b, open-label trial. Adults with obesity but without type 2 diabetes were randomized 1:1 to the maximum tolerated dose of weekly tirzepatide (10 mg or 15 mg) or weekly semaglutide (1.7 mg or 2.4 mg) for 72 weeks. The primary endpoint was percent change in body weight. Key secondary endpoints were the share of people reaching at least 10%, 15%, 20%, and 25% weight loss, and the change in waist circumference. [1]

Two design choices shape how to read it. First, each arm used the maximum tolerated dose, so people who could not tolerate the top dose stayed on a lower one. That mirrors real prescribing, and it means the trial compares two treatment strategies rather than two fixed doses. Second, everyone enrolled was free of type 2 diabetes, so the result speaks most directly to people seeking treatment for obesity alone. [1]

The results

751 participants were randomized. [1]

Both differences were statistically significant (P less than 0.001), and people on tirzepatide were more likely to reach each of the 10%, 15%, 20%, and 25% weight loss thresholds. [1]

The most common adverse events in both groups were gastrointestinal, mostly mild to moderate and mostly during dose escalation. [1]

How it fits with earlier trials

The result lines up with what the placebo-controlled trials suggested. In SURMOUNT-1, tirzepatide at 15 mg produced a mean weight change of minus 20.9% at 72 weeks versus minus 3.1% on placebo. [3] In STEP 1, semaglutide 2.4 mg produced minus 14.9% at 68 weeks versus minus 2.4%. [4] SURMOUNT-5 confirms that gap directly, in one population, under one protocol.

It also echoes SURPASS-2, the earlier head-to-head trial in type 2 diabetes. There tirzepatide at 5, 10, and 15 mg lowered HbA1c and body weight more than semaglutide 1 mg, with weight change of minus 7.6 to minus 11.2 kg versus minus 5.7 kg. [2] Note that SURPASS-2 used the diabetes dose of semaglutide, lower than the obesity dose tested in SURMOUNT-5.

Our semaglutide vs tirzepatide comparison lays out both trials alongside mechanism, labels, and regulatory status.

What the trial does not tell you

Four limits matter when you read the headline number.

1. Open label. Everyone knew which drug they were on. Weight is an objective measure, which limits the bias, but behavior and dropout can still differ when people know their assignment. [1]
2. Sponsor. The trial was funded by the manufacturer of tirzepatide. [1] That does not make the result wrong, and the trial was registered and published in a major journal, but independent replication would strengthen it.
3. No hard outcomes. SURMOUNT-5 measured weight and waist size. Semaglutide has a completed cardiovascular outcomes trial in obesity without diabetes: in SELECT, it lowered the risk of major adverse cardiovascular events by 20% versus placebo (hazard ratio 0.80). [5] Wegovy carries that cardiovascular indication on its label, and the tablet form does too. [7]
4. Averages, not individuals. Some people on semaglutide lose more than some people on tirzepatide. Tolerability, other conditions, and coverage often decide the choice in practice.

Label differences worth knowing

Both labels carry a boxed warning about thyroid C-cell tumors seen in rodents. [6] [7] Their approved uses differ. Zepbound is approved for weight reduction in adults and for moderate to severe obstructive sleep apnea in adults with obesity. [6] Wegovy injection is approved for weight reduction in adults and adolescents aged 12 and older, cardiovascular risk reduction, and noncirrhotic MASH with moderate to advanced fibrosis. [7] Those indications can decide what an insurer will cover.

What it means for access

For most people the practical question is not which drug wins a trial but which one they can get. Coverage often follows the indication on the prescription, and the tirzepatide cost page and semaglutide cost page break out list, self-pay, insurance, and telehealth prices. For Medicare Part D enrollees who qualify, the Medicare GLP-1 Bridge covers Wegovy (injection or tablet) and the Zepbound KwikPen at a 50 USD monthly copay from July 1, 2026, with prior authorization. [8]

The obesity condition page grades every option we track, and the GLP-1 hub collects every drug in the class with its regulatory status.