Ozempic vs Mounjaro: what's the difference?

Ozempic and Mounjaro get mentioned in the same breath a lot. They're both weekly shots for type 2 diabetes, and they work in similar ways. But they aren't the same medicine. Here's what's different, straight from each one's prescribing information: Ozempic and Mounjaro.

What's the core difference between Ozempic and Mounjaro?

Think of a receptor as a lock on a cell, and a hormone as the key that opens it. After you eat, your gut releases hormones that act as keys, including GLP-1 (Holst, 2007).

• Ozempic (semaglutide) is one key for one lock. Its label calls it a GLP-1 receptor agonist with 94% sequence homology to human GLP-1.
• Mounjaro (tirzepatide) is one key that fits two locks. Its label calls it a GIP receptor and GLP-1 receptor agonist, built on the GIP sequence. GIP and GLP-1 are both hormones your body makes; the label calls them native GIP and GLP-1.

The same two molecules are sold under other names for other uses: semaglutide as Wegovy and tirzepatide as Zepbound. Since January 2026, the name Ozempic also covers a daily semaglutide tablet (label). This article compares the weekly shots.

What are Ozempic and Mounjaro each approved for?

How do they work on blood sugar?

Two hormones from your pancreas move blood sugar in opposite directions. Insulin helps sugar get into your cells for energy (NIDDK). Glucagon tells your liver to release stored sugar (MedlinePlus).

• Ozempic raises insulin and lowers glucagon in a glucose-dependent way: the effect kicks in when blood sugar is high.
• Mounjaro boosts both the fast first wave and the slower second wave of insulin release and lowers glucagon, also glucose-dependent. Its label adds that it increased insulin sensitivity in a clamp study after 28 weeks.

Both slow the stomach, but their labels describe it differently. Ozempic's label calls it a minor delay in stomach emptying early after a meal. Mounjaro's label says the delay is largest after the first dose and gets smaller over time.

How long does each one last?

Both carry a fatty acid that lets them hold on to albumin, a protein in your blood, which keeps them around for days. Semaglutide's is a C18 fatty acid; tirzepatide's is a C20.

• Ozempic: half-life about 1 week. It peaks 1 to 3 days after a shot, reaches a steady level after 4 to 5 weeks, and stays in your blood for about 5 weeks after the last dose.
• Mounjaro: half-life about 5 days. It peaks 8 to 72 hours after a shot and reaches a steady level after 4 weeks.

How is dosing different?

These are general facts from each label about how the dose steps work. Your prescriber decides your dose and when it changes.

• Ozempic starts at 0.25 mg once a week for 4 weeks, then goes to 0.5 mg. The highest dose on the label is 2 mg once a week.
• Mounjaro starts at 2.5 mg once a week. Steps go up by 2.5 mg after at least 4 weeks on a dose. The highest dose for adults is 15 mg once a week.
• The milligrams don't compare. They're different molecules, so 15 mg of one isn't “more” than 2 mg of the other.

What if you miss a dose?

• Ozempic: take it as soon as you can within 5 days. If more than 5 days have passed, skip it and take the next dose on your usual day.
• Mounjaro: take it as soon as you can within 4 days (96 hours). If more than 4 days have passed, skip it and take the next dose on your usual day.
• Changing your shot day: the labels need at least 2 days between doses for Ozempic, and at least 3 days for Mounjaro.

How do the side effects compare?

The most common side effects are similar: nausea, diarrhea, vomiting and constipation, mostly while the dose is going up. Here are nausea rates from each label's placebo-controlled trials. The labels say rates from different trials can't be compared directly, so read each row against its own placebo, not against the other medicine.

Both labels carry a boxed warning about thyroid C-cell tumors, seen in rodents.

What's different about birth control?

This is a real label difference. Mounjaro may make birth control pills work less well, because of the slower stomach. Its label says to switch to a non-oral method, or add a barrier method, for 4 weeks after starting and for 4 weeks after each dose increase. Birth control that isn't taken by mouth shouldn't be affected.