Victoza is made with liraglutide. Mounjaro is made with tirzepatide. Both are FDA-approved medicines for type 2 diabetes in adults and in children aged 10 and older. Both are also approved to lower the risk of heart attack, stroke, and heart-related death in some adults with type 2 diabetes. For Victoza, that means adults who already have heart or blood vessel disease. For Mounjaro, it means adults at high risk of these events. For weight management, liraglutide is approved as Saxenda and tirzepatide as Zepbound, each with its own label.
Each label lists the side effects seen in that product's own placebo-controlled trials. The tables below copy those numbers. Placebo means a shot with no medicine in it. A problem in a table is not proof that the medicine caused it.
The two tables come from separate trials with different people and different lengths. The Victoza trials lasted at least 26 weeks each. The Mounjaro trials lasted 40 weeks, and one of them added Mounjaro to long-acting insulin. They do not come from one trial that tested Victoza and Mounjaro against each other.
The boxed warning on each label
- Victoza (liraglutide): The Victoza label has a boxed warning, FDA's strongest kind. Liraglutide caused thyroid C-cell tumors in rats and mice. It is not known whether it causes them in people, including medullary thyroid cancer (MTC). People with a personal or family history of MTC, or with a condition called MEN 2, must not use it. The label lists signs of a thyroid tumor to watch for: a lump in the neck, trouble swallowing, shortness of breath, or hoarseness that does not go away.
- Mounjaro (tirzepatide): The Mounjaro label has a boxed warning, FDA's strongest kind. Tirzepatide caused thyroid C-cell tumors in rats. It is not known whether it causes them in people, including medullary thyroid cancer (MTC). People with a personal or family history of MTC, or with a condition called MEN 2, must not use it. The label lists signs of a thyroid tumor to watch for: a lump in the neck, trouble swallowing, shortness of breath, or hoarseness that does not go away.
Stopping because of stomach and bowel problems
- Victoza label: in the diabetes trials, 4.3% of adults on Victoza stopped because of stomach or bowel problems, compared with 0.5% on placebo.
- Mounjaro label: in the diabetes trials, 3.0% to 6.6% of adults on Mounjaro stopped because of stomach or bowel problems, compared with 0.4% on placebo.
- The Victoza label says most stops for stomach and bowel problems came in the first 2 to 3 months. The Mounjaro label does not say when people stopped. It says most nausea, vomiting, and diarrhea happened while the dose was being raised and became less common over time.
Compare each number with its own placebo number, not with the other label.
Victoza vs Mounjaro: side effect tables
Both labels list problems that reached 5% of people on the medicine and were more common than on placebo. The Victoza middle column covers two dose groups, so one Victoza group can be under 5% or equal to placebo. The Mounjaro middle column shows the lowest and highest share across three dose groups.
A problem missing from one table may still have happened, below 5% or no more often than on placebo. Low blood sugar is left out of both tables. The labels warn that it may be more likely when either medicine is taken with insulin or a diabetes medicine called a sulfonylurea.
Compare each Victoza or Mounjaro number with its own placebo number, not with the other table.
Victoza label
Victoza trials in adults with type 2 diabetes At least 26 weeks each
Adults with type 2 diabetes in 5 trials. The table counts 1,669 adults on Victoza in two dose groups and 661 on placebo.
| Reported problem | Victoza groups | Placebo |
|---|---|---|
| Nausea | 18% to 20% | 5% |
| Diarrhea | 10% to 12% | 4% |
| Headache | 10% to 11% | 7% |
| Colds (nose and throat infections) | 9% to 10% | 8% |
| Vomiting | 6% to 9% | 2% |
| Less hunger | 9% to 10% | 1% |
| Indigestion (dyspepsia) | 4% to 7% | 1% |
| Upper airway infections | 6% to 7% | 6% |
| Constipation | 5% | 1% |
| Back pain | 4% to 5% | 3% |
Source for Victoza trials in adults with type 2 diabetes: Victoza prescribing information on DailyMed , label revised .
Mounjaro label
Mounjaro trials in adults with type 2 diabetes 40 weeks
Adults with type 2 diabetes in 2 trials. One tested Mounjaro alone. The other added it to long-acting insulin, with or without metformin. 718 adults took Mounjaro in three dose groups and 235 took placebo.
| Reported problem | Mounjaro groups | Placebo |
|---|---|---|
| Nausea | 12% to 18% | 4% |
| Diarrhea | 12% to 17% | 9% |
| Less appetite | 5% to 11% | 1% |
| Vomiting | 5% to 9% | 2% |
| Constipation | 6% to 7% | 1% |
| Indigestion (dyspepsia) | 5% to 8% | 3% |
| Belly pain | 5% to 6% | 4% |
Source for Mounjaro trials in adults with type 2 diabetes: Mounjaro prescribing information on DailyMed , label revised .
What these numbers do not show
- The labels say side-effect rates from one medicine's trials cannot be directly compared with rates from another medicine's trials.
- Both labels list more warnings, and problems reported after approval, such as pancreatitis that can be deadly and blocked bowels. How often these happen is not known.
- The Victoza label does not recommend using it with other products made with liraglutide, such as Saxenda.
- There are rare reports of people on GLP-1 medicines breathing stomach contents into the lungs during surgery or deep sedation. Both labels say to tell the care team before any planned surgery or procedure.
- The Mounjaro label says it may make birth control pills work less well, because it slows how fast the stomach empties. That slowing is largest after the first dose and fades over time. The label advises switching to a non-pill method or adding a barrier method, such as condoms, for 4 weeks after starting and for 4 weeks after each dose increase.
- Each label covers its own uses. Ask the prescriber before changing, stopping, or combining any of these medicines or other diabetes medicines.
- Trials can miss rare harms and harms that take years to appear.
- These numbers describe Victoza and Mounjaro. They do not describe compounded tirzepatide or liraglutide, or products sold online as research peptides.
Full tables, notes, and warnings
Report a side effect
You can report a suspected side effect to the FDA at 1-800-FDA-1088 or through FDA MedWatch . If a reaction feels serious, get medical care first.
Other label comparisons
- Zepbound vs Wegovy: side effects in the weight-management labels
- Mounjaro vs Ozempic: side effects in the type 2 diabetes labels
- Mounjaro vs Zepbound: the same medicine in the diabetes and weight labels
- Ozempic vs Wegovy: the same medicine in the diabetes and weight labels
- Saxenda vs Zepbound: side effects in the weight-management labels
- Victoza vs Saxenda: the same medicine in the diabetes and weight labels
- Victoza vs Ozempic: side effects in the type 2 diabetes labels
- Saxenda vs Wegovy: side effects in the weight-management labels
- Forteo vs Tymlos: side effects in the osteoporosis labels