Four brand names, two molecules. It is worth getting this straight before anything else, because a great deal of confusion downstream begins here.
| Brand | Molecule | Approved for |
|---|---|---|
| Ozempic | Semaglutide | Type 2 diabetes |
| Wegovy | Semaglutide | Chronic weight management |
| Mounjaro | Tirzepatide | Type 2 diabetes |
| Zepbound | Tirzepatide | Chronic weight management |
Same drug, different label, different dose ceiling, and — critically for Americans — very different coverage treatment.
What the trials show on weight
Across the pivotal programs, tirzepatide has produced greater average weight reduction than semaglutide at their respective top doses. This has since been supported by head-to-head comparison. The direction of the finding is not seriously disputed.
~15%
Approximate mean weight reduction, semaglutide 2.4 mg, 68 weeks, in the pivotal obesity trial
~21%
Approximate mean weight reduction, tirzepatide 15 mg, 72 weeks, in the pivotal obesity trial
Averages
Individual response varies enormously in both directions
Those are averages from different trials with different populations, which is why the head-to-head evidence matters more than a side-by-side of two press releases.
Why the more effective drug is not automatically the right one
Several things can outweigh a few percentage points of average efficacy.
Coverage
The best drug you cannot obtain is worse than the second-best drug you can. In practice, formulary position decides this question for a large share of American patients before any clinical reasoning happens.
Tolerability
Side effect profiles are broadly similar in kind, but individual response is not. Plenty of people tolerate one and not the other, and there is no way to know in advance.
Established outcome data
Semaglutide has the longer track record and a broader set of completed cardiovascular and renal outcome trials. Tirzepatide’s outcome program is younger. For a patient whose primary concern is cardiovascular risk rather than weight, the depth of evidence is a legitimate consideration.
The indication you actually have
If you have obstructive sleep apnea, or established cardiovascular disease, or type 2 diabetes, the approved indication may determine both the clinical choice and the coverage outcome.
What should not decide it
Whichever one your neighbor is on. Whichever one is in the news. Whichever one a telehealth advertisement is currently promoting. And whichever one is cheapest from a source you cannot verify.
The choice between these molecules is usually made by a formulary, occasionally by a side effect, and almost never by a patient reading a trial.
The practical version
Take the efficacy difference seriously but not decisively. Bring your coverage situation to the appointment, because it will shape the realistic options more than anything else. And treat the first choice as provisional — switching between agents is common, unremarkable, and frequently the right call. The mechanics, including the fact that you restart at the bottom of the new ladder rather than carrying your dose across, are in switching between GLP-1s.
That switch is much easier to make well with a record of the first attempt. How much weight, over how long, at which doses, with which side effects and on which days — a clinician weighing a change is otherwise working from your summary of a year you were not taking notes on. Whatever you use is fine. Zenday keeps dose, weight and symptoms on a single timeline, which happens to be the format that answers this particular question.