Based on the strongest clinical evidence available, tirzepatide (brand name Zepbound) produces more weight loss than any other currently approved GLP-1 medication. In the first head-to-head trial comparing the two leading options, tirzepatide delivered an average of 20.2% body weight loss over 72 weeks, while semaglutide (Wegovy) achieved 13.7%. That’s a 47% difference in effectiveness, which for a 250-pound person translates to roughly 50 pounds lost versus 34.
But “best” depends on more than peak numbers. Cost, availability, side effects, and how your body responds all matter. Here’s what you need to know about each option and how they compare.
How Tirzepatide Compares to Semaglutide
The head-to-head trial, published in 2025, settled a question that years of separate clinical trials had only hinted at. People taking tirzepatide were twice as likely to lose 25% or more of their body weight compared to those on semaglutide. Nearly two-thirds of tirzepatide users (65%) lost at least 15% of their weight, versus 40% on semaglutide. These are significant margins, not small statistical differences.
Tirzepatide’s standalone trial results tell a similar story. At the highest approved dose (15 mg), participants lost an average of 22.5% of their body weight, roughly 52 pounds, over 72 weeks. The middle dose (10 mg) produced a 21.4% loss, and even the lowest maintenance dose (5 mg) delivered 16%. Placebo, for comparison, produced just 2.4%.
Semaglutide remains highly effective in its own right. A 13.7% average weight loss is more than triple what older weight loss medications typically achieve, and for many people it’s enough to meaningfully reduce the health risks associated with carrying excess weight.
Why Tirzepatide Works Differently
The key difference is that these two drugs don’t work through the same pathway. Semaglutide targets one receptor: GLP-1. Tirzepatide targets two: GLP-1 and a second gut hormone receptor called GIP. This dual action is why tirzepatide is sometimes called a “dual agonist” rather than a pure GLP-1 drug, though it’s grouped in the same category.
GLP-1 slows stomach emptying, suppresses appetite, and triggers insulin release after meals. These effects are shared by both medications. GIP adds a separate layer. It acts on appetite-regulating areas of the brain to further reduce food intake, and it influences how the body stores and breaks down fat. The combination appears to produce a synergistic effect: the two hormones working together achieve more than either would alone.
What Taking These Medications Looks Like
Both Zepbound and Wegovy are once-weekly injections you give yourself at home, typically in the stomach, thigh, or upper arm. They use small, pen-style devices that make the process straightforward.
Neither drug starts at its full dose. Zepbound begins at 2.5 mg weekly for the first four weeks, a dose that’s purely for getting your body adjusted and isn’t considered a treatment dose. After that, you move to 5 mg, which is the lowest maintenance dose. From there, your prescriber can increase by 2.5 mg every four weeks or longer, up to a maximum of 15 mg. Wegovy follows a similar gradual ramp-up over several months. This slow titration exists to reduce the severity of side effects, particularly nausea.
Most people reach their target dose within three to five months. Weight loss continues to accumulate for roughly 12 to 18 months before plateauing, though maintaining the lost weight requires staying on the medication.
Side Effects Are Similar for Both
The side effect profiles of tirzepatide and semaglutide overlap almost entirely, and they’re driven by the same GLP-1 mechanism. A large 2025 survey of real-world users found that about half of all people taking a GLP-1 medication experience nausea at some point, though only about 9% describe it as serious. Roughly a third report diarrhea, and about one in five experience vomiting.
For most people, these symptoms are worst during the first few weeks on a new dose and fade as the body adjusts. The slow dose increases are specifically designed to make this manageable. Eating smaller meals, avoiding high-fat foods, and staying hydrated all help. Some people tolerate one medication better than the other, which is one practical reason semaglutide remains an important option even though tirzepatide produces greater average weight loss.
All GLP-1 medications carry an FDA boxed warning for people with a personal or family history of medullary thyroid cancer or a condition called Multiple Endocrine Neoplasia type 2. If either runs in your family, these drugs are not an option.
Cost and Access Still Matter
Neither Zepbound nor Wegovy is inexpensive. Without insurance, both carry list prices above $1,000 per month. Insurance coverage varies widely. Some plans cover one but not the other, and many still require documentation of failed diet attempts or a minimum BMI before approving coverage. Both medications experienced supply shortages through much of 2023 and 2024, though the FDA has determined that both semaglutide and tirzepatide injection shortages are now resolved as of early 2025.
If one medication is covered by your insurance and the other isn’t, that coverage gap likely matters more than the difference in average weight loss between them. Both produce clinically meaningful results.
What’s Coming Next
A third drug called retatrutide is in late-stage clinical trials and targets three hormone receptors instead of two: GLP-1, GIP, and glucagon. The glucagon receptor adds yet another mechanism, increasing energy expenditure and promoting fat breakdown. In a Phase 3 trial in people with type 2 diabetes, the highest dose of retatrutide produced 16.8% weight loss in just 40 weeks, a shorter timeframe than the 72-week trials for tirzepatide and semaglutide. Earlier Phase 2 data in people without diabetes suggested even larger losses over a full treatment course. The addition of glucagon receptor activation appears to boost calorie burning in a way the current drugs don’t.
Retatrutide is not yet FDA-approved and likely won’t be available until 2026 or later. For now, tirzepatide and semaglutide are the two primary options, and tirzepatide holds a clear edge in the amount of weight lost on average. The right choice between them depends on your insurance, how you tolerate each drug, and what your prescriber recommends based on your full health picture.