Zepbound is not purely a GLP-1 drug. It activates GLP-1 receptors, but it also activates a second hormone receptor called GIP, making it a dual-action medication. This distinction matters because the added GIP activity appears to be a major reason Zepbound produces greater weight loss than GLP-1-only drugs like Wegovy.
How Zepbound Differs From Pure GLP-1 Drugs
GLP-1 drugs like semaglutide (sold as Wegovy and Ozempic) work by mimicking a single gut hormone: glucagon-like peptide-1. This hormone slows digestion, reduces appetite, and helps regulate blood sugar. Zepbound’s active ingredient, tirzepatide, mimics that same hormone but adds a second one: glucose-dependent insulinotropic peptide, or GIP. Both hormones are naturally released by your gut after eating, and both play roles in metabolism and appetite signaling.
Interestingly, tirzepatide was built by engineering GLP-1 activity into a GIP-based molecule. Research published in JCI Insight found that the drug actually engages the GIP receptor more strongly than the GLP-1 receptor, binding to GIP receptors with the same strength as the body’s natural GIP but attaching to GLP-1 receptors about five times more weakly than natural GLP-1. Scientists describe this as an “imbalanced” dual agonist that leans toward GIP. The combination of strong GIP activation and a distinctive pattern of GLP-1 signaling is thought to explain why tirzepatide outperforms drugs that target GLP-1 alone.
Weight Loss Results Compared to Semaglutide
In the SURMOUNT-1 trial, participants taking Zepbound for 72 weeks lost 15% of their body weight at the lowest dose (5 mg), 19.5% at the middle dose (10 mg), and nearly 21% at the highest dose (15 mg). These are averages, meaning some people lost more and some lost less.
A head-to-head trial called SURMOUNT-5, involving 751 people with obesity but without type 2 diabetes, directly compared tirzepatide to semaglutide at their maximum doses over 72 weeks. Participants on tirzepatide lost about 50 pounds (20.2% of body weight) compared to 33 pounds (13.7%) for semaglutide. Nearly a third of people on tirzepatide lost at least 25% of their body weight, compared to 16% of those on semaglutide. This gap in effectiveness is one reason the “dual agonist” distinction is more than a technicality.
Zepbound vs. Mounjaro
Zepbound and Mounjaro contain the exact same active ingredient (tirzepatide) and are both manufactured by Eli Lilly. The difference is their FDA-approved use. Mounjaro is approved for type 2 diabetes. Zepbound is approved for chronic weight management in adults with obesity (BMI of 30 or higher) or overweight (BMI of 27 or higher) with at least one weight-related condition like high blood pressure, type 2 diabetes, or high cholesterol. Zepbound also has an approval for moderate to severe obstructive sleep apnea in adults with obesity. Insurance coverage and pricing can differ between the two brands even though the medication inside is identical.
How Zepbound Is Taken
Zepbound is a once-weekly injection that comes in six dose levels: 2.5 mg, 5 mg, 7.5 mg, 10 mg, 12.5 mg, and 15 mg. Everyone starts at 2.5 mg, which is purely a starting dose to let your body adjust. The dose is then gradually increased, typically every four weeks, until you and your prescriber find an effective maintenance dose. The 2.5 mg, 7.5 mg, and 12.5 mg doses exist only as stepping stones during this ramp-up period. Skipping dose levels to get to a higher dose faster is not recommended, as it can cause more severe side effects and setbacks.
Common Side Effects
The most frequently reported side effects are gastrointestinal: nausea, diarrhea, vomiting, constipation, indigestion, and stomach pain. Other common complaints include belching, gas, acid reflux, bloating, fatigue, injection site reactions, hair loss, and heartburn. These GI side effects tend to be worst during the dose-escalation phase and improve once your body adjusts to a stable dose. That said, more people stopped taking Zepbound due to GI problems compared to those taking a placebo in clinical trials. An increased heart rate was also reported more frequently in people taking Zepbound.
Cost
Eli Lilly lists the wholesale price of Zepbound at $499 to $1,086 per fill, depending on the dose. What you actually pay depends heavily on your insurance plan, pharmacy, and any discount programs you qualify for. Coverage varies widely, as many insurers still treat weight management medications differently from other chronic disease drugs.