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A neutral, sourced look at how tirzepatide and semaglutide compare. See also the matching semaglutide-focused version of this comparison in the Semaglutide forum.

Receptor targets

Semaglutide activates the GLP-1 receptor only. Tirzepatide activates both the GIP and GLP-1 receptors. That added GIP activity is the core mechanistic difference between the two.

Research findings

Semaglutide’s pivotal obesity trial is STEP 1 (NEJM, 2021): 2.4 mg produced average weight loss of about 14.9% at 68 weeks. Tirzepatide’s pivotal obesity trial is SURMOUNT-1 (NEJM, 2022): 15 mg produced average weight loss of about 22.5% at 72 weeks. These are separate trials in different populations — not a head-to-head result.

Similarities

Both are once-weekly injectables (semaglutide also now has an FDA-approved oral tablet form), both work through the incretin hormone system, and both have approved indications spanning type 2 diabetes and chronic weight management. Both also now carry cardiovascular-relevant data: semaglutide (Wegovy) has an FDA-approved indication for reducing cardiovascular death/MI/stroke risk in adults with cardiovascular disease and obesity/overweight (the SELECT trial), while tirzepatide’s SURPASS-CVOT trial (NEJM, 2025) showed noninferiority to dulaglutide on major cardiovascular outcomes in type 2 diabetes, though this has not resulted in a separate FDA cardiovascular indication for tirzepatide as of this writing.

Differences

Beyond the receptor mechanism, tirzepatide (Zepbound) carries an FDA approval for obstructive sleep apnea that semaglutide does not have. Semaglutide (Ozempic) carries an FDA approval for reducing kidney disease progression and cardiovascular death in type 2 diabetes with chronic kidney disease (the FLOW trial) that tirzepatide does not currently have.

Study limitations

Cross-trial comparisons (like the weight-loss percentages above) are confounded by differences in trial populations, duration, and design — they’re suggestive, not definitive. Treat any “X% vs. Y%” comparison, including the one in this post, as a starting point for reading the actual trials, not a final answer.

Why individual reports are not clinical evidence

A member’s personal outcome reflects one person’s biology, adherence, diet, and circumstances. It’s useful context, but it doesn’t generalize the way a controlled trial does — please don’t treat anecdotes (including your own) as proof of anything.

This thread is for comparing published research and mechanisms — not for personalized recommendations about which compound to use.

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