Zepbound's weight results come from a 72-week trial, so the honest answer to "how long" is measured in months. Weight starts to fall within the first few weeks. The large averages people quote, around 20%, are what the trial found after a year and a half [1]. This page walks through that timeline using the label and the published trial. For the drug itself, see the Zepbound guide.
The trial behind the label ran for 72 weeks
Zepbound's weight-loss label rests mainly on SURMOUNT-1, published in 2022 [4]. It enrolled 2,539 adults with obesity, or with overweight and at least one weight-related condition, and excluded people with type 2 diabetes [1]. Each person was assigned to 5 mg, 10 mg or 15 mg once a week, or to placebo.
Two details shape the timeline. First, nobody started on their assigned dose; the trial raised doses gradually over as long as 20 weeks. Second, everyone also got diet and activity counseling, so the placebo group is people trying hard without the drug. The main result was measured at week 72, after at least 52 weeks on the assigned dose [1].
In the first three months, every dose group moves together
Every Zepbound prescription starts at 2.5 mg a week. The label is plain that this dose "is for treatment initiation and is not approved as a maintenance dosage" [1]. Its job is to let your stomach adjust. Your prescriber then raises the dose at the pace the label sets; the steps are covered in Zepbound dosage.
The label's time-course chart for SURMOUNT-1 (Figure 3) shows what that means. Weight is already lower at week 4 in all three dose groups, and the early slope is steep. Through about week 12 the three groups move together, because everyone is still climbing toward their dose. After that the lines separate, with 10 mg and 15 mg pulling away from 5 mg. The curves are still dropping at week 36 and level off toward week 60 to 72 [1].
By week 72, average loss was 15% to 21%, depending on dose
Here is where people ended up after 72 weeks. The percentages are the average change from starting weight, counting everyone who was randomized, including people who stopped early [1].
| Group | Average change | Lost at least 5% | Lost at least 20% |
|---|---|---|---|
| Placebo | −3.1% | 34.5% | 3.1% |
| Zepbound 5 mg | −15.0% | 85.1% | 30.0% |
| Zepbound 10 mg | −19.5% | 88.9% | 50.1% |
| Zepbound 15 mg | −20.9% | 90.9% | 56.7% |
Zepbound prescribing information, Table 2 (Study 1, intention-to-treat population) [1].
In pounds, 20.9% of a 230-pound starting weight is about 48 pounds, by our arithmetic. More than half of the people on 15 mg lost a fifth of their body weight or more. That's the payoff of the long middle stretch, not of the first month.
| Group | Lost at least 10% | Lost at least 15% |
|---|---|---|
| Placebo | 18.8% | 8.8% |
| Zepbound 5 mg | 68.5% | 48.0% |
| Zepbound 10 mg | 78.1% | 66.6% |
| Zepbound 15 mg | 83.5% | 70.6% |
Zepbound prescribing information, Table 2 (Study 1) [1].
A second trial shows where people stood at week 36
SURMOUNT-4 gives a useful midpoint. Everyone took open-label tirzepatide for the first 36 weeks, and by the end of that stretch 93% of the people who went on in the trial were on 15 mg. Their average loss at week 36 was 20.9% [1]. That figure counts only people who stayed in the trial to week 36, so it runs higher than an everyone-counted average would. It still shows that much of the loss arrives in the first eight or nine months.
Put the two trials together and a rough shape appears. The chart's steepest stretch is the first six months. Between months six and nine the drop slows, and after that the line flattens; the later weeks are more about holding the loss than adding to it. The dose you reach decides how far down the line ends.
With type 2 diabetes, the averages were a few points lower
A second 72-week trial enrolled 938 adults with type 2 diabetes and a BMI of 27 or more. Average loss was 12.8% on 10 mg and 14.7% on 15 mg, against 3.2% on placebo [1]. Wegovy's label shows the same pattern for semaglutide: 14.9% in its main trial without diabetes, 9.6% in its trial with diabetes [3].
Mounjaro is the same molecule, tirzepatide, but its label is for blood sugar control in type 2 diabetes, not weight loss [2]. So Mounjaro's own trials measured weight as a side result. The doses and pens match; the labeled use is what differs. See Zepbound vs Mounjaro for the full comparison.
Why you might be losing less than the trial average
An average hides a spread. The label's own example: at 15 mg, about 83.5% of people lost at least 10% of their weight by week 72 [1]. Turn that around and roughly 1 in 6 did not reach 10%, even on the top dose. A few reasons the label and trial design point to:
- You're still early. Months one to three run at lower doses, and the trial's dose groups only separate after that.
- Your dose is lower. On 5 mg the average was 15.0%; on 15 mg it was 20.9%. Which maintenance dose fits you depends on response and tolerance, and that's your prescriber's call.
- The trial included counseling. Everyone in SURMOUNT-1 also got diet and activity support, and the results reflect that package.
- Compounded tirzepatide isn't the product that was tested. Compounded tirzepatide isn't FDA-approved, the FDA doesn't review it for safety or effectiveness, and it doesn't check its quality before it ships. No trial has measured how it compares; see does compounded tirzepatide work?
If your weight has stalled, bring it to your prescriber rather than changing anything on your own. Side effects can also shape the pace; Zepbound side effects covers when they tend to show up.
The results last only as long as the treatment does
SURMOUNT-4 tested what happens after the early months. Everyone took tirzepatide for 36 weeks and lost an average of 20.9%. Then half switched to placebo. From week 36 to week 88, the placebo group regained 14.0% of body weight, while those who stayed on lost another 5.5% [5]. The full picture, including the semaglutide trials, is in what happens when you stop a GLP-1.
Plan the cost for a year, not a month
Because results build over a year or more, the monthly price matters more than the first-month offer. Brand Zepbound prices are in Zepbound cost. Compounded tirzepatide runs $85–$433 a month across programs on this site, with the trade-offs above; see compounded tirzepatide cost and the compounded tirzepatide scores.
To see what a full year costs at the price you're quoted, including membership fees and four-week billing, use the monthly cost calculator. For how semaglutide's timeline compares, see how long Wegovy takes to work and the tirzepatide guide.