Mounjaro vs Ozempic: Which GLP-1 Works Better?

Two medications dominate the GLP-1 conversation right now: Ozempic (semaglutide) and Mounjaro (tirzepatide). Both are injectable, once-weekly medications that suppress appetite, lower blood sugar, and produce substantial weight loss. Both have generated massive demand and supply shortages.

But they're not the same drug — and the efficacy data clearly favors one of them. Here's a complete breakdown.

The Mechanism Difference: Single vs. Dual Agonist

This is the key distinction.

Ozempic (semaglutide) is a GLP-1 receptor agonist. It mimics the glucagon-like peptide-1 hormone, which is released after eating. GLP-1 receptors are found throughout the body — in the pancreas (where it stimulates insulin release), the gut (where it slows gastric emptying), and the brain (where it reduces appetite and food reward).

Mounjaro (tirzepatide) is a dual GLP-1 and GIP receptor agonist. In addition to activating GLP-1 receptors, it also activates glucose-dependent insulinotropic polypeptide (GIP) receptors. GIP is another incretin hormone with its own effects on insulin secretion, fat storage, and energy metabolism.

The synergistic effect of activating both receptor types appears to produce greater metabolic benefit than activating GLP-1 alone — which is exactly what the clinical trials show.

Efficacy Data: Weight Loss

This is where tirzepatide's advantage becomes stark.

Semaglutide 2.4 mg (STEP 1 trial): Mean weight loss of 14.9% of body weight over 68 weeks in patients with obesity.

Tirzepatide (SURMOUNT-1 trial): - 5 mg dose: Mean weight loss of 15.0% - 10 mg dose: Mean weight loss of 19.5% - 15 mg dose: Mean weight loss of 20.9%

At the highest tirzepatide dose, nearly half of participants (48%) achieved at least 20% weight loss. In the STEP 1 semaglutide trial, about 32% reached that threshold.

The SURMOUNT-5 trial directly compared tirzepatide vs semaglutide head-to-head in adults with obesity and found tirzepatide produced 47% more weight loss on average than semaglutide. That's a meaningful clinical difference.

Efficacy Data: Blood Sugar Control

Both medications significantly lower HbA1c (a measure of long-term blood sugar control), but tirzepatide again outperforms:

In the SURPASS trial program comparing tirzepatide directly to semaglutide 1.0 mg in type 2 diabetes patients, tirzepatide 10 mg and 15 mg produced greater HbA1c reduction than semaglutide 1.0 mg at every dose level.

Ozempic lowers HbA1c by approximately 1.5–2.0 percentage points. Mounjaro lowers HbA1c by approximately 2.0–2.5 percentage points at higher doses.

Both are clinically meaningful. Tirzepatide edges ahead.

Side Effect Profiles

Both medications share a similar side effect profile, driven primarily by their GI mechanism:

• Nausea (most common)
• Vomiting
• Diarrhea
• Constipation
• Decreased appetite (intended, but occasionally excessive)

The rate of GI side effects is comparable between the two medications, though some real-world data suggests tirzepatide may be slightly better tolerated — possibly because the dual mechanism achieves greater efficacy at lower effective GLP-1 stimulation compared to a single high-dose GLP-1 agonist.

Both medications carry a boxed warning for thyroid C-cell tumors (based on rodent studies; human relevance uncertain) and pancreatitis.

Neither should be used in patients with a personal or family history of medullary thyroid carcinoma or Multiple Endocrine Neoplasia syndrome type 2 (MEN2).

Cost Comparison

This is where things get complex.

Branded Mounjaro: ~$1,060–$1,100/month without insurance Branded Ozempic: ~$935–$1,000/month without insurance Branded Zepbound (tirzepatide for weight loss): ~$1,060–$1,100/month

As of 2026, compounded tirzepatide is still available (tirzepatide remains on the FDA shortage list as of this writing), typically at $150–$350/month through telehealth providers. This maintains the substantial cost advantage of the compounded route.

Compounded semaglutide faces a more uncertain regulatory environment following FDA shortage resolution determinations in early 2025 — access is more variable.

Which One Should You Choose?

If efficacy is the top priority: Tirzepatide. The data is unambiguous — it produces greater weight loss and better glycemic control at equivalent or comparable side effect burden.

If you've already been on semaglutide and it's working: There's no urgent reason to switch. "Working" means different things to different patients — if you've achieved your goals on semaglutide at a tolerable dose, don't fix what isn't broken.

If cost is the constraint and compounded access is a concern: Given the more stable compounding access for tirzepatide right now, it may actually be the more pragmatic choice for patients starting fresh.

If you have type 2 diabetes and your insurer covers one but not the other: Work with your prescriber to get coverage for whatever is on formulary. Both produce clinically meaningful blood sugar control.

The bottom line: if you're choosing from scratch and want the most effective GLP-1 available, the evidence points to tirzepatide. Marrow's clinicians can help you evaluate which protocol makes the most sense for your specific situation.