Because the medicine is still in your body. According to the FDA labels, semaglutide (Ozempic, Wegovy) has a half-life of about one week and stays in the circulation for about 5 to 7 weeks after the last dose, and tirzepatide (Mounjaro, Zepbound) has a half-life of about 5 days. Appetite returns gradually, and the habits you built keep working for a while, so a few more weeks of slow loss is normal.
What is not expected is weight loss you are not trying for that carries on for months, or that comes with other symptoms. That deserves a doctor's look.
How long the medicine keeps working after the last dose
A half-life is the time it takes for the amount of a medicine in your body to fall by half. Wegovy's prescribing information gives semaglutide an elimination half-life of about one week and states it will be present in the circulation for about 5 to 7 weeks after the last dose. Zepbound's prescribing information gives tirzepatide a half-life of about 5 days.
So the week after your last injection, a large share of the medicine is still active, which is also why side effects after stopping fade over weeks rather than days. A week later, roughly half of that. The appetite effect tapers away over a month or more, not overnight, and while it is fading you are often still eating less than your body now needs. The result is a little more weight loss than you expected.
Why Mounjaro and Zepbound clear a little sooner
A common rule of thumb in pharmacology is that a medicine is mostly gone after about five half-lives. With semaglutide's half-life of about a week, that lines up with the 5 to 7 weeks in Wegovy's label. With tirzepatide's half-life of about 5 days, the same rule puts most of it gone in roughly three and a half to four weeks.
So if you stopped Mounjaro or Zepbound, the window of continued appetite suppression is usually a little shorter than after Ozempic or Wegovy. It is still weeks, not days. Searches for "still losing weight after stopping Mounjaro" have risen sharply over the past year, and the half-life is most of the answer. The rest is how your body and routine respond as the effect fades, which varies from person to person.
None of this is a guide to timing anything with your medication. It only explains why the scale can keep drifting down for a while after the last injection.
Why regain in the trials was gradual, not instant
The withdrawal trials measured weight over a year, and none of them show a sudden rebound in the first weeks.
In the STEP 1 extension, people regained 11.6 percentage points of their lost weight over the year after stopping semaglutide. In SURMOUNT-4, published in JAMA, people switched from tirzepatide to placebo gained 14 percent over 52 weeks. Those are year-long totals, and what happens when you stop Wegovy breaks the semaglutide data down further. Combined with how slowly the medicines clear, they fit the pattern many people describe: a quiet few weeks, sometimes still drifting down, and then a slow turn upward.
We go through the tirzepatide data in more detail in will you regain weight after stopping Zepbound.
Habits from treatment keep working for a while
Months on a GLP-1 change routines. Smaller plates, earlier dinners, less grazing, a protein-first breakfast, fewer drinks with friends. Those habits do not disappear with the medicine. For the first weeks they often carry on almost automatically, and they keep doing some of the work the drug was doing.
That is good news, and it is also the period to make the useful habits deliberate rather than automatic. When appetite returns properly, the routines you chose on purpose are the ones that last.
The scale itself can mislead in the first weeks
Day-to-day weight moves with water, salt and digestion. If constipation eases after stopping, or you eat less salt than usual during a quieter week, the morning number can dip without any change in fat.
That is why a single low reading should not be read as a trend either way. Judge the direction from a 7 day average, as explained in how often you should weigh yourself.
When ongoing weight loss is a reason to see your doctor
A little extra loss in the weeks after stopping is expected. Some patterns are not, and should be checked rather than explained away: weight loss you are not trying for that continues for months after the medicine has cleared, loss together with ongoing vomiting, trouble swallowing, pain, night sweats, unusual tiredness, or a big change in bowel habits, and feeling unable to eat enough even when hungry.
A review of unintentional weight loss in American Family Physician notes that, in older adults, common causes include digestive conditions, psychiatric conditions such as depression, and cancer, and that medications can contribute through nausea or taste changes. It is not a reason to panic. It is a reason not to wait. Bring your weight history so your doctor can see the timeline.
How to watch the turn as it happens
The period after stopping is when most people stop weighing, often because the news has been good. It is also when the trend is most informative. OffRamp keeps a 7 day average against your baseline, the weight you set when you started, and every morning says whether you are holding steady or drifting up. The Regain Radar only calls drift when that average sits 2 percent above baseline for 7 days in a row, so the slow turn shows up early without false alarms.
If the trend keeps falling instead, OffRamp can export a PDF of your weigh-in history, with your current 7 day average and change since starting, to take to an appointment. Whatever the numbers show, decisions about your medication stay with your prescriber.
