Tirzepatide (sold as Zepbound) produces the most weight loss of any currently approved injection, averaging about 14.7% of body weight over two years in real-world data. Semaglutide (Wegovy) comes in second at roughly 10.8%. But “best” depends on more than raw numbers. Cost, dosing schedule, side effects, and how your body responds all play a role in which injection works best for you specifically.
The Four FDA-Approved Options
Four injectable medications are currently approved for chronic weight management in the U.S. Two get the most attention, and two serve narrower purposes.
- Tirzepatide (Zepbound) is a weekly injection that mimics two gut hormones involved in appetite regulation and blood sugar control. It consistently produces the largest weight loss in studies.
- Semaglutide (Wegovy) is also a weekly injection but targets only one of those gut hormones. It was the first of the modern weight loss injections to gain widespread use.
- Liraglutide (Saxenda) works through the same single-hormone pathway as semaglutide but requires a daily injection and produces less weight loss, typically around 5% to 7% of body weight over a year.
- Setmelanotide (Imcivree) is a daily injection approved only for people with specific rare genetic obesity conditions. It works through a completely different brain pathway and isn’t prescribed for general weight management.
For the vast majority of people searching for weight loss injections, the real comparison comes down to tirzepatide and semaglutide.
Tirzepatide vs. Semaglutide: Weight Loss Results
A large real-world study comparing the two medications over two years found that tirzepatide produced a mean weight reduction of 14.7% (about 16 kg or 35 pounds), while semaglutide produced 10.8% (about 11.6 kg or 25.5 pounds). That gap held up across different patient groups.
The difference was even more dramatic among strong responders. About 42.6% of people on tirzepatide lost 15% or more of their body weight within the first year, compared to 21.6% on semaglutide. Tirzepatide also worked slightly faster on a month-to-month basis. The likely reason for the advantage is that tirzepatide activates two hormone pathways instead of one, giving it a stronger effect on appetite suppression and how the body processes calories.
Liraglutide falls well behind both. In a 56-week clinical trial, people taking liraglutide lost an average of 7.4% of their body weight, compared to 3% with a placebo. For people with type 2 diabetes, the result was closer to 5.4%. Because it also requires daily injections rather than weekly ones, liraglutide is now mostly considered a fallback option when the newer medications aren’t available or tolerated.
What Side Effects to Expect
All GLP-1 based injections share a similar side effect profile. Nausea, vomiting, diarrhea, and constipation are by far the most common problems, and they tend to be worst during the first few weeks as your dose gradually increases. Most people find these symptoms ease over time as the body adjusts.
Less common but more serious risks include pancreatitis (inflammation of the pancreas causing severe abdominal pain), gastroparesis (delayed stomach emptying that can cause persistent nausea and bloating), bowel obstruction, and gallstone attacks. These are uncommon, but they’re worth knowing about, especially if you have a history of gallbladder or pancreatic problems.
Side effect rates are broadly similar between tirzepatide and semaglutide. The dose escalation schedule exists specifically to reduce gastrointestinal symptoms. With liraglutide, for example, you start at a low dose and increase weekly over five weeks before reaching the full dose. Semaglutide and tirzepatide follow a similar ramp-up pattern.
The Muscle Loss Question
One concern you’ll hear about is losing muscle along with fat. In clinical trials of both semaglutide and tirzepatide, roughly 40% of the total weight lost came from lean body mass, which is higher than the roughly 25% typically seen with diet-based weight loss. That sounds alarming, but it needs context.
Lean body mass isn’t just muscle. It includes organs, bones, water stored in tissues, and even the structural components within fat tissue itself. When someone loses a significant amount of body fat, the supporting structures around that fat shrink too, registering as “lean mass” loss on a scan. Researchers have noted that current body composition measurements can’t cleanly separate true skeletal muscle loss from these other changes. That said, adding resistance training while on these medications is widely recommended to preserve as much muscle as possible.
What Happens When You Stop
This is one of the most important things to understand before starting. These medications work for as long as you take them. A systematic review published in The Lancet found that people regained about 60% of their lost weight within one year of stopping treatment. Beyond that, the regain was estimated to plateau at roughly 75% of the weight originally lost.
The rate of regain follows a predictable curve, with about half the rebound happening in the first 23 weeks after stopping. This doesn’t mean the medications “don’t work.” It means the biological signals that drive weight gain, particularly appetite and metabolic regulation, reassert themselves once the drug is removed. For many people, this means treatment is ongoing rather than a short course.
Cost Without Insurance
Both manufacturers cut prices for self-pay patients in early 2025. Wegovy (semaglutide) now costs $499 per month through Novo Nordisk’s direct pricing. Zepbound (tirzepatide) starts at $349 per month for the lower starter doses and goes up to $499 per month at higher maintenance doses through Eli Lilly’s self-pay program. These prices apply to people who are uninsured or whose insurance doesn’t cover weight loss medications.
With insurance, your cost can vary enormously. Some plans cover these medications with a specialty copay, while others exclude weight loss drugs entirely. Checking your formulary before committing to a prescription can save you from a surprise bill at the pharmacy.
Practical Details: Storage and Injection
All of these medications come as prefilled injection pens designed for self-administration at home. The injection goes under the skin, typically in the abdomen, thigh, or upper arm, and the needles are small enough that most people describe the sensation as mild.
The pens need to be stored in the refrigerator between 36°F and 46°F. If you’re traveling or can’t refrigerate immediately, pens can stay at room temperature (up to 86°F) for up to 28 days. After that, or if a pen has been frozen or exposed to heat above 86°F, it needs to be discarded. Keeping pens in their original cartons protects them from light.
Which One Is Right for You
If maximum weight loss is the priority and cost isn’t a barrier, tirzepatide (Zepbound) has the strongest clinical evidence. It produces about 4 percentage points more weight loss than semaglutide on average, and nearly twice as many people achieve the 15% loss threshold that tends to meaningfully improve obesity-related health conditions.
Semaglutide (Wegovy) remains a strong option, especially if tirzepatide isn’t covered by your insurance or isn’t available due to supply issues. A 10.8% average weight reduction is still clinically significant and life-changing for many people. Liraglutide (Saxenda) is generally reserved for situations where weekly injections aren’t suitable or the newer options can’t be tolerated.
Regardless of which injection you use, the weight loss depends on sustained treatment. The data on regain after stopping is clear enough that most clinicians frame these as long-term medications rather than temporary interventions. Combining any of these injections with strength training and dietary changes gives you the best chance of preserving muscle and maintaining results.