MounjarovsZepbound

Mounjaro's active ingredient, tirzepatide, is a "dual agonist" that activates two gut-hormone receptors at once: GIP (glucose-dependent insulinotropic polypeptide) and GLP-1 (glucagon-like peptide-1). Most older drugs in this class hit only GLP-1. By stimulating both, tirzepatide prompts the pancreas to release insulin when blood sugar is high, lowers the glucagon hormone that raises blood sugar, slows how fast the stomach empties, and reduces appetite. The net effect is better blood-sugar control and, as a downstream benefit, significant weight loss. A built-in fatty-acid chain lets it bind to blood albumin, giving it a long half-life so it only needs to be injected once a week.

Zepbound's active drug, tirzepatide, is a once-weekly injection that activates two gut-hormone receptors at once: GLP-1 and GIP. This "dual agonist" design is what sets it apart from GLP-1-only drugs like Wegovy. By mimicking these hormones, it curbs appetite, increases fullness, and slows how fast the stomach empties, so most people eat less and feel satisfied longer. It also improves how the body releases insulin and handles blood sugar. The result is sustained calorie reduction without the constant hunger that derails many diets.

In SURPASS-2, an open-label 40-week head-to-head trial of 1,879 adults with type 2 diabetes published in the New England Journal of Medicine (2021), tirzepatide beat injectable semaglutide 1 mg. In the primary (treatment-regimen) analysis, the 15 mg dose lowered A1C by about 2.30 percentage points and reduced body weight by roughly 11.2 kg (about 12% from a baseline near 94 kg), and the 5 mg dose lowered A1C by about 2.01 points with about 7.6 kg lost — versus 1.86 points and 5.7 kg with semaglutide. (In the secondary on-treatment analysis, 15 mg figures were larger, about 2.46 points and 12.4 kg.) About 60% of participants on 15 mg hit a combined target of A1C 6.5% or lower plus at least 10% weight loss, compared with 22% on semaglutide. In the separate SURPASS-CVOT outcomes trial (about 13,300 patients with type 2 diabetes and established atherosclerotic heart disease, ~4-year median follow-up, published in NEJM in 2025), tirzepatide was non-inferior to dulaglutide for major adverse cardiovascular events (HR 0.92) and showed a 16% lower rate of all-cause death (HR 0.84), alongside greater A1C and weight reductions. These trials were in people with type 2 diabetes; your results may differ.

In the pivotal 72-week SURMOUNT-1 trial (2,539 adults with obesity or overweight, without type 2 diabetes; published in the New England Journal of Medicine in 2022), tirzepatide produced average body-weight reductions of about 16.0% at 5 mg, 21.4% at 10 mg, and 22.5% at 15 mg, versus roughly 2.4% with placebo. In the head-to-head SURMOUNT-5 trial (751 participants, 72 weeks, NEJM 2025), Zepbound beat Wegovy (semaglutide) with an average 20.2% weight loss versus 13.7%, a 47% greater relative reduction; about 31.6% of Zepbound users lost at least 25% of their body weight versus 16.1% on Wegovy. Zepbound is also FDA-approved (December 2024) for moderate-to-severe obstructive sleep apnea in adults with obesity, where the SURMOUNT-OSA program showed clinically meaningful reductions in the apnea-hypopnea index versus placebo. Individual results vary with dose, diet, and activity.

The most common side effects are gastrointestinal: nausea, diarrhea, decreased appetite, vomiting, constipation, indigestion, and abdominal pain. These are usually mild to moderate, most pronounced when starting and after each dose increase, and tend to ease over days to weeks. Serious but less common risks include acute pancreatitis (severe, persistent stomach pain — seek care immediately), gallbladder problems and gallstones (more likely during rapid weight loss), severe low blood sugar especially when combined with insulin or sulfonylureas, kidney injury from dehydration due to vomiting or diarrhea, allergic reactions, and possible worsening of diabetic retinopathy. The boxed warning concerns thyroid C-cell tumors seen in rodents; whether this risk applies to humans is unknown, so watch for a neck lump, hoarseness, trouble swallowing, or persistent shortness of breath and tell your doctor. Report any severe or persistent symptoms to your prescriber.

The most common side effects are gastrointestinal and tend to appear during dose increases: nausea (reported in roughly 25-30% of users across the pivotal trials, and as high as the mid-30s in some studies), diarrhea, vomiting, constipation, abdominal pain, indigestion, and fatigue or injection-site reactions. These are usually mild-to-moderate and ease over time with slow titration, though they lead a small percentage of people to stop treatment. Less common but serious risks include pancreatitis (severe persistent abdominal pain), gallbladder problems including gallstones, acute kidney injury (often from dehydration due to vomiting or diarrhea), severe allergic reactions, and low blood sugar when combined with insulin or sulfonylureas. Zepbound carries an FDA boxed warning for thyroid C-cell tumors seen in rodent studies; whether it causes them in humans is unknown, but it is contraindicated in people with a personal or family history of medullary thyroid cancer or MEN 2. Seek care promptly for severe stomach pain, signs of an allergic reaction, or vision changes.

As of September 2026, LillyDirect lists Mounjaro's self-pay price as starting at $499/month for a one-month supply at every strength from 2.5 mg to 15 mg. Without that program, pharmacy cash prices run roughly $1,000 or more per month. With commercial insurance that covers Mounjaro for type 2 diabetes, Lilly's savings card can lower the copay for eligible patients (caps apply; not available with Medicare, Medicaid, TRICARE or VA coverage). Medicare Part D may cover Mounjaro for type 2 diabetes but not for weight loss. Confirm pricing and coverage before starting.

As of September 2026, LillyDirect's regular self-pay price for a one-month Zepbound KwikPen supply is $299 for 2.5 mg, $399 for 5 mg, $499 for 7.5 mg and $699 for 10 mg, 12.5 mg or 15 mg; Lilly's Zepbound Journey Program can lower the higher-dose prices if you refill on schedule. Self-pay pricing can't be combined with insurance. With commercial insurance that covers Zepbound, Lilly's savings card can reduce the copay for eligible patients (monthly and annual caps apply). Coverage for weight loss varies by plan, so confirm your own benefits before starting, and budget for an ongoing monthly cost — it is a long-term medication.

Mounjaro is FDA-approved as an add-on to diet and exercise to improve blood sugar control in adults and pediatric patients 10 years and older with type 2 diabetes. It is NOT FDA-approved for weight loss or for type 1 diabetes. It should NOT be used by anyone with a personal or family history of medullary thyroid carcinoma (MTC) or Multiple Endocrine Neoplasia syndrome type 2 (MEN 2) — this is a boxed warning. Avoid or use with caution if you have a history of pancreatitis, severe gastrointestinal disease such as gastroparesis, diabetic retinopathy, or known hypersensitivity to tirzepatide. It is not recommended in pregnancy. Because delayed stomach emptying can reduce absorption of oral pills, Lilly advises people using oral hormonal contraceptives to switch to a non-oral method or add a barrier method for four weeks after starting and for four weeks after each dose increase. Discuss kidney issues and any history of gallbladder disease with your prescriber.

Zepbound is approved for adults with obesity (BMI 30 or higher) or overweight (BMI 27 or higher) plus at least one weight-related condition such as high blood pressure, high cholesterol, or type 2 diabetes, and for moderate-to-severe obstructive sleep apnea in adults with obesity. It is meant to be used alongside a reduced-calorie diet and more physical activity. Do NOT use it if you or a family member has had medullary thyroid carcinoma (MTC) or Multiple Endocrine Neoplasia syndrome type 2 (MEN 2), or if you have had a serious allergic reaction to tirzepatide. It is not for use in pregnancy and is not approved for children. Use caution with a history of pancreatitis, gallbladder disease, kidney problems, or severe gastrointestinal disease, and tell your doctor if you take insulin or sulfonylureas (which raise low-blood-sugar risk). Your prescriber makes the final eligibility call.