Tirzepatide, sold as Zepbound for weight and Mounjaro for type 2 diabetes, produced one of the largest weight losses of any approved medicine in its main trial: up to about 21 percent at the highest dose over 72 weeks. That average hides two facts that matter if the scale has stopped moving for you. Roughly one in ten people on the highest dose in that trial did not lose even 5 percent, and when people stopped the medicine in a later study, they regained about 14 percent of their weight within a year. This guide explains how tirzepatide is supposed to work over time, why weight loss stalls, what to check with your prescriber, and the trials designed for people it has not helped enough.
How tirzepatide is supposed to work over time
Tirzepatide acts on two gut hormone receptors, GLP-1 and GIP, and like semaglutide it is started low and raised in steps. Zepbound begins at 2.5 mg and can be increased every four weeks up to 15 mg, so reaching the top doses takes about five months. In the SURMOUNT-1 trial, weight loss continued through most of the 72 weeks before flattening, and higher doses produced more loss: about 15 percent at 5 mg, 19.5 percent at 10 mg, and 20.9 percent at 15 mg on average. Mounjaro contains the same medicine at the same doses but is approved for type 2 diabetes, so people using it for weight may be held at lower doses chosen for blood sugar. If you are still climbing the dose ladder, the medicine has not yet shown what it can do.
Why you may not be losing weight on Zepbound or Mounjaro
Dose and timing. The most common reason: a low maintenance dose kept for side effects, or too little time on it.
The plateau. Weight loss slows as the body defends its new weight, with a lower resting metabolism and stronger hunger signals. In the trials this happened after roughly a year to eighteen months. A plateau at 15 to 20 percent below your starting weight is the expected course, not a failure.
Eating and drinking around the medicine. Tirzepatide reduces hunger; it does not change the calories in alcohol, sweet drinks, or snacks eaten without hunger.
Other medicines or conditions. Steroids, insulin, some antidepressants and antipsychotics, beta blockers, and untreated thyroid disease or sleep apnea all push against weight loss. Zepbound is itself approved, since December 2024, for moderate to severe sleep apnea in people with obesity, which is worth knowing if sleep is part of the picture.
Unapproved products. Compounded tirzepatide is not FDA approved, and the FDA has warned about dosing errors with vials and online products. If your medicine did not come from a pharmacy as a branded Zepbound or Mounjaro pen, or as Lilly's own Zepbound vials, mention it.
Non response.On the highest dose in SURMOUNT-1, about 9 in 10 people lost at least 5 percent; about 1 in 10 did not, and the share was higher on lower doses. The reasons are being studied, and the newer medicines in trials exist largely for this group.
What doctors usually do next
Check the dose and how consistently it is taken, review other medicines, screen for sleep apnea and thyroid problems, and add structured support, which the trials included for everyone. If you have reached a plateau, the goal usually shifts to keeping the weight off, because the SURMOUNT-4 study showed what happens otherwise: people switched to placebo regained about 14 percent of their weight in a year while those who continued lost a further 5.5 percent. Other options include newer medicines, such as the Wegovy pill (approved December 2025) and Lilly's Foundayo pill (approved April 2026), and, for some people, weight loss surgery. These are prescriber decisions, and this article is not a substitute for that conversation. Our weight loss treatment trials page covers what is approved and what is being tested; if you are on semaglutide instead, our Ozempic and Wegovy guide covers that medicine.
Trials built for people tirzepatide has not helped enough
Because regain after stopping is now a known problem, trials of medicines to maintain weight after a GLP-1 or GIP medicine are recruiting, and they specifically want people who lost weight on tirzepatide or semaglutide. Trials of new oral medicines recruit people who want an alternative to injections. And for people with type 2 diabetes whose blood sugar is still not at goal on tirzepatide, add on trials exist. Some general obesity trials exclude recent GLP-1 use, so read each listing carefully; the ones below are designed for your situation.
Studies recruiting now for exactly this situation
A Phase 2 trial of ALV-100 for maintaining weight loss enrolls adults who have lost at least 10 percent of their weight on a GLP-1 or GIP based medicine and have been on a stable dose for at least three months, at 12 US sites. A Phase 2 trial of a new Lilly medicine enrolls adults with type 2 diabetes not at their blood sugar goal on a stable dose of tirzepatide or semaglutide, at 25 US sites. A Phase 3 trial of ASC30, a once daily oral GLP-1, enrolls adults with overweight or obesity who also have type 2 diabetes, at 6 US sites recruiting now. Each listing states its own rules, and applying takes about 5 minutes.
Common questions
Why am I not losing weight on Mounjaro? Most often because you are still on a lower dose, because weight loss has reached its plateau, or because eating patterns, other medicines, or an untreated condition are working against it. Mounjaro is dosed for blood sugar, so people using it for weight are often on less than the trials used.
How long does a Zepbound plateau last? In the trials, weight generally leveled off after a year or more and then held steady as long as the medicine continued.At that dose, the plateau is usually where your weight settles; the question becomes maintenance rather than more loss.
What percentage of people do not lose weight on tirzepatide? In SURMOUNT-1, about 1 in 10 people on the highest dose did not lose at least 5 percent of their weight at 72 weeks. At the highest dose, more than half lost 20 percent or more, so response varies widely.
Can I join a trial if I am already taking Zepbound? Some trials exclude recent GLP-1 or GIP use, but maintenance and add on studies are designed for people already on these medicines. The listing says which, and any change is coordinated with your prescriber; do not stop a medicine to qualify without that conversation.
See weight loss treatment trials recruiting now
Browse open studies, filter by location, and apply in about 5 minutes: Weight Loss Treatment Clinical Trials