Semaglutide vs. tirzepatide: the real difference
Semaglutida vs. tirzepatida: cuál es la diferencia real
Illustrative image. Does not represent guaranteed results.
The technical difference fits in one line: semaglutide acts on one receptor, GLP-1. Tirzepatide acts on two, GLP-1 and GIP.
The practical difference lives in two trials published in the New England Journal of Medicine. And there is a detail almost no comparison article mentions: those two trials never compared the medications to each other. Each was compared against placebo, in different populations, over different periods.
Key points
- Semaglutide acts on the GLP-1 receptor. Tirzepatide acts on GLP-1 and also on GIP.
- In STEP 1, semaglutide 2.4 mg showed −14.9% body weight at 68 weeks, versus −2.4% on placebo.
- In SURMOUNT-1, tirzepatide showed −15.0%, −19.5% and −20.9% at 72 weeks by dose, versus −3.1% on placebo.
- These are separate trials with different populations and durations — not a head-to-head comparison.
- In both, the most common adverse events were gastrointestinal and clustered during dose escalation.
In this article
One receptor versus two
GLP-1 is a hormone your gut releases when you eat. It signals the pancreas and the brain that food has arrived. Medications in this class mimic that signal.
GIP is another gut hormone in the same family. Tirzepatide activates both pathways. That is the whole mechanistic difference, and it is why it is sometimes described as "dual."
Does two mechanisms automatically mean better?
Not necessarily, and it matters to be precise here. It means it acts through two pathways. The trial numbers are what they are — but as you will see, they come from studies that were not designed to be compared with each other.
The numbers, side by side and with the caveat
| Trial | Weight change |
|---|---|
| STEP 1 · semaglutide 2.4 mg · 68 weeks | −14.9% |
| STEP 1 · placebo | −2.4% |
| SURMOUNT-1 · tirzepatide 5 mg · 72 weeks | −15.0% |
| SURMOUNT-1 · tirzepatide 10 mg | −19.5% |
| SURMOUNT-1 · tirzepatide 15 mg | −20.9% |
| SURMOUNT-1 · placebo | −3.1% |
The temptation is to subtract and draw a conclusion. Before you do, three things:
One. These are different trials with different participants. In SURMOUNT-1, mean starting weight was 104.8 kg and mean BMI 38.0. STEP 1 had different criteria. Comparing percentages across different populations is not the same as comparing them within one study.
Two. The durations differ: 68 weeks versus 72.
Three. These are averages. In STEP 1, 50.5% of participants lost 15% or more — which also means nearly half lost less. An average is not a forecast.
Side effects in both
In both trials the pattern was the same: the most common adverse events were gastrointestinal, mostly mild to moderate, and appeared primarily during dose escalation.
In STEP 1, 4.5% discontinued for gastrointestinal events versus 0.8% on placebo. In SURMOUNT-1, discontinuation for adverse events was 4.3%, 7.1% and 6.2% at the 5, 10 and 15 mg doses, versus 2.6% on placebo.
Worth noting: in SURMOUNT-1 discontinuation did not rise linearly with dose. The highest figure was at the middle dose. Trials are rarely as tidy as the summaries.
What actually decides which one fits
Almost never the table above. A licensed clinician reviews your full medical history, your labs, your current medications and your existing conditions. Individual digestive tolerance, availability and coverage also factor in.
And there is something no comparison resolves: which medication you will be able to sustain. As the discontinuation data shows, the effect depends on continued treatment. The better medication on paper is worth nothing if you cannot keep it.
Who is this NOT for?
If you expect this article to tell you which one to pick, it will not — and anyone who does so without seeing your labs is selling, not advising.
Neither is appropriate with a personal or family history of medullary thyroid carcinoma or multiple endocrine neoplasia type 2, nor during pregnancy or if you are trying to conceive.
If you have prior pancreatitis, gallbladder disease, gastroparesis or kidney disease, the decision requires specific clinical evaluation before starting.
And a note on compounded versions: compounded medications contain the same active ingredient class but are not FDA-approved finished pharmaceuticals. The percentages on this page come from trials of the branded products. They do not transfer automatically.
Frequently asked questions
So is tirzepatide better?
The published SURMOUNT-1 percentages are higher than STEP 1, but they come from separate trials with different populations and durations. That is not the same as head-to-head. What is appropriate for you is determined by a licensed clinician.
Which has fewer side effects?
In both trials the profile was similar: mostly gastrointestinal, mild to moderate, concentrated during dose escalation. Discontinuation rates were the same order of magnitude in both.
Can I switch from one to the other?
That is a clinical decision. It depends on your tolerance, your response and your history. It is not something to adjust on your own.
Does the compounded version give the same results?
The trials cited here used branded products. Compounded medications contain the same active ingredient class but are not FDA-approved finished pharmaceuticals, and no trials of this scale exist for them.
What is the catch?
That the question "which is better" distracts from the one that matters: which one you can sustain. The discontinuation evidence is decisive for both.
What if my insurance only covers one?
That is a legitimate consideration and worth raising in the first conversation with the clinician, not later.
Do you offer support in Spanish?
Yes. All of our content and support is available in Spanish.
Sources
- Wilding JPH, et al. Once-Weekly Semaglutide in Adults with Overweight or Obesity (STEP 1). N Engl J Med. 2021;384(11):989-1002. — DOI
- Jastreboff AM, et al. Tirzepatide Once Weekly for the Treatment of Obesity (SURMOUNT-1). N Engl J Med. 2022;387(3):205-216. — DOI
- Wilding JPH, et al. Weight regain and cardiometabolic effects after withdrawal of semaglutide: the STEP 1 trial extension. Diabetes Obes Metab. 2022;24(8):1553-1564. — DOI
- FDA. Compounding and the FDA: Questions and Answers. — U.S. Food and Drug Administration
This article is informational and is not medical advice. SCTS1 does not prescribe medication. All medical care, prescriptions, and treatment plans are provided by licensed healthcare providers through our partner platform. Treatment eligibility is determined by a licensed provider. Compounded medications contain the same active ingredient class but are not FDA-approved finished pharmaceuticals. Individual results vary and are not guaranteed.