Tirzepatide is a prescription injectable medication used to treat type 2 diabetes and chronic obesity. It is sold under two brand names: Mounjaro, approved by the FDA in 2022 for blood sugar control in type 2 diabetes, and Zepbound, approved in 2023 specifically for weight management. Both are the same drug given as a once-weekly injection under the skin, but each targets a different condition with its own prescribing criteria.
How Tirzepatide Works
Tirzepatide is the first and only FDA-approved medication that activates two gut hormone receptors at once: GIP and GLP-1. Older medications in this class, like semaglutide (Ozempic, Wegovy) and liraglutide, only activate the GLP-1 receptor. This dual action is what sets tirzepatide apart.
Both GIP and GLP-1 are hormones your gut naturally releases after eating. They signal your pancreas to produce more insulin when blood sugar rises, which is why tirzepatide lowers blood sugar without a high risk of pushing it dangerously low. The two hormones also act on satiety centers in the brain, reducing appetite and helping you feel full sooner. On the fat metabolism side, they work in complementary ways to maintain healthier fat cells and reduce fat buildup in organs like the liver.
Type 2 Diabetes
Mounjaro is prescribed alongside diet and exercise to improve blood sugar control in adults with type 2 diabetes. Across the SURPASS clinical trial program, tirzepatide produced substantial drops in A1C, the blood test that reflects average blood sugar over roughly three months. At the highest dose (15 mg), between 43% and 62% of participants brought their A1C below 5.7%, a level considered normal for someone without diabetes. Those who reached that threshold saw an average A1C reduction of about 3 percentage points.
These results are notably larger than what earlier diabetes medications typically achieve. For many participants, tirzepatide moved their blood sugar from a clearly diabetic range into a range that would no longer meet the diagnostic criteria for diabetes.
Chronic Weight Management
Zepbound is approved for long-term weight management in adults who meet specific BMI thresholds. You’re eligible if your BMI is 30 or greater (classified as obesity), or 27 or greater if you also have at least one weight-related health condition such as high blood pressure, high cholesterol, type 2 diabetes, obstructive sleep apnea, or cardiovascular disease.
Like the diabetes indication, Zepbound is meant to be used alongside a reduced-calorie diet and increased physical activity, not as a standalone treatment. Clinical trials showed significant weight loss across all doses, with participants on the highest dose losing an average of roughly 15% or more of their body weight over about a year.
Obstructive Sleep Apnea
Tirzepatide has also shown striking results for obstructive sleep apnea, a condition closely tied to excess weight where breathing repeatedly stops during sleep. In the SURMOUNT-OSA trial, participants with obesity and moderate-to-severe sleep apnea were treated for 52 weeks. Those on tirzepatide experienced roughly 25 to 29 fewer breathing interruptions per hour compared to about 5 fewer in the placebo group. That translated to a nearly 48% to 56% reduction in the severity of their sleep apnea. Notably, these benefits held whether or not participants were also using a CPAP machine.
Fatty Liver Disease (MASH)
One of the more promising areas of investigation is tirzepatide’s effect on metabolic dysfunction-associated steatohepatitis, commonly called MASH. This is a progressive form of fatty liver disease that can lead to scarring (fibrosis) and eventually liver failure. In a phase 2 trial published in the New England Journal of Medicine, 190 participants with biopsy-confirmed MASH and significant liver scarring received tirzepatide or a placebo for 52 weeks.
The results were dramatic. At the highest dose, 62% of participants saw their liver inflammation resolve without any worsening of scarring, compared to just 10% on placebo. Liver enzyme levels, a marker of liver damage, dropped by roughly 50% across all tirzepatide doses. Participants also lost between 10.7% and 15.6% of their body weight depending on dose, which likely contributed to the liver improvements. About half of participants on tirzepatide also saw at least one stage of improvement in their liver scarring. While not yet FDA-approved for this use, these results suggest tirzepatide could become a meaningful treatment for a disease that currently has very few options.
Dosing and How It’s Taken
Tirzepatide is injected once a week under the skin, typically in the abdomen, thigh, or upper arm. Everyone starts at 2.5 mg for the first four weeks. This initial dose is not a treatment dose. It’s designed to let your body adjust and minimize side effects. After four weeks, the dose increases to 5 mg. From there, your doctor can raise the dose in 2.5 mg steps every four weeks or longer, based on how you respond. The maximum dose is 15 mg per week.
This slow escalation is important. Most side effects occur during dose increases, so the gradual ramp-up gives your digestive system time to adapt.
Common Side Effects
Digestive side effects are the most frequent issue. In the weight management trials, nausea affected 25% to 33% of participants depending on dose, compared to about 10% on placebo. Diarrhea occurred in 19% to 23% of participants (versus 7% on placebo), and vomiting in 8% to 12% (versus 2% on placebo). These symptoms were most common during dose escalation and tended to decrease over time as the body adjusted.
For most people, these side effects are mild to moderate and temporary. Eating smaller meals, avoiding high-fat foods, and staying hydrated can help manage nausea during the adjustment period.
Who Should Not Take Tirzepatide
Tirzepatide carries a boxed warning, the FDA’s most serious safety label, related to thyroid tumors. In animal studies, drugs in this class caused a type of thyroid cancer called medullary thyroid carcinoma. It is not known whether tirzepatide causes the same risk in humans, but as a precaution, the medication is contraindicated for anyone with a personal or family history of medullary thyroid carcinoma, or a genetic condition called Multiple Endocrine Neoplasia syndrome type 2 (MEN 2).
Tirzepatide is also not approved for type 1 diabetes. It works by enhancing your body’s own insulin response, which requires functioning insulin-producing cells, something type 1 diabetes fundamentally lacks.