If you're weighing semaglutide vs tirzepatide, you've probably noticed that most comparisons stop at “tirzepatide works better.” That's an incomplete answer. The two drugs work through different receptors, they're dosed on different scales, and the one that suits you depends on your history and how you tolerate the first few weeks.
What's the actual difference between semaglutide and tirzepatide?
That's worth being precise about, because tirzepatide is often lumped in as “a GLP-1” in casual conversation. It does act on GLP-1, but the second mechanism is what separates it from everything else in the class.
| Factor | Semaglutide | Tirzepatide |
|---|---|---|
| Receptors targeted | GLP-1 only | GIP and GLP-1 (dual agonist) |
| Brand name for weight | Wegovy | Zepbound |
| Brand name for type 2 diabetes | Ozempic | Mounjaro |
| FDA approval for weight management | 2021 | 2023 |
| How it's taken | Once-weekly subcutaneous injection | Once-weekly subcutaneous injection |
| Dose range for weight | 0.25 mg up to 2.4 mg weekly | 2.5 mg up to 15 mg weekly |
| Average weight loss in its own trial | 14.9% at 68 weeks (STEP-1) | 16.0% to 22.5% at 72 weeks (SURMOUNT-1) |
| Head-to-head result | 13.7% at 72 weeks (SURMOUNT-5) | 20.2% at 72 weeks (SURMOUNT-5) |
| Most common side effects | Nausea, diarrhoea, vomiting, constipation | Nausea, diarrhoea, vomiting, constipation |
One thing that table can't show: the milligram numbers aren't comparable. 15 mg of tirzepatide isn't “six times stronger” than 2.4 mg of semaglutide. They're different molecules on different scales, and reading across the dose row is the most common mistake people make with this comparison.
How each one works in the body
Both drugs mimic gut hormones your body already makes after a meal. GLP-1 signals fullness to the brain, prompts the pancreas to release insulin when glucose is high, reduces glucagon, and slows how quickly the stomach empties. Semaglutide does all of that by occupying the GLP-1 receptor.
Tirzepatide adds GIP, a second incretin hormone involved in insulin release and fat metabolism. Activating both receptors appears to work better together than either does alone, which is the leading explanation for the larger weight reductions seen in tirzepatide's trials. If you want the background on the single-agonist side of the comparison, we've written separately on what semaglutide is and how it works.
How they're dosed
Both start low and climb slowly, and both use four-week steps. Semaglutide for weight management begins at 0.25 mg weekly and moves through 0.5, 1.0, and 1.7 mg to a maintenance dose of 2.4 mg. Tirzepatide begins at 2.5 mg weekly, steps up to 5 mg after four weeks, and can increase in 2.5 mg increments to maintenance doses of 5, 10, or 15 mg.
The starting dose in both cases isn't there to drive weight loss. It's there to let your gastrointestinal system adapt before you reach the range where the drug actually does its work. Our compounded semaglutide dosage chart walks through what each step is doing.
Not sure which of the two you should be on?
A licensed clinician reviews your history, your goals, and your tolerance before recommending either one.
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What the trials actually show
Tirzepatide has produced larger average weight loss in every comparison run so far. In STEP-1, published in the New England Journal of Medicine in 2021, participants on semaglutide 2.4 mg lost an average of 14.9% of body weight over 68 weeks. In SURMOUNT-1, published in 2022, participants on tirzepatide lost between 16.0% and 22.5% over 72 weeks depending on dose.
Those were separate trials with separate populations, so SURMOUNT-5 put the two drugs against each other directly. Over 72 weeks, participants on the maximum tolerated dose of tirzepatide lost 20.2% of body weight against 13.7% on the maximum tolerated dose of semaglutide.
Read those numbers as averages, not forecasts. Individual response varies widely, and plenty of people do very well on semaglutide. What you do underneath the medication matters too, which is why we cover preventing muscle loss on GLP-1 medications as a core part of the program.
Side effects and safety
The side effect profiles are close enough that they rarely decide the choice on their own. Most effects are gastrointestinal, they're worst in the days after a dose increase, and they usually ease as your body adapts. In the FDA prescribing information for Wegovy, reported rates were nausea 44%, diarrhoea 23%, vomiting 15%, and constipation 11%.
Common side effects include:
- Nausea, particularly in the first week after stepping up
- Diarrhoea or constipation
- Vomiting and abdominal discomfort
- Reduced appetite and feeling full much earlier than usual
- Fatigue in the first few weeks
- Redness, swelling, or itching at the injection site
The serious risks are shared. Both carry a boxed warning for thyroid C-cell tumours and aren't prescribed to anyone with a personal or family history of medullary thyroid carcinoma or multiple endocrine neoplasia type 2. Pancreatitis has been reported with both, and low blood sugar becomes a real concern if either drug is combined with insulin or a sulfonylurea. Our week-by-week guide to tirzepatide side effects covers what's normal and what isn't.
Call your provider if you can't keep fluids down, or if you develop severe abdominal pain that doesn't settle.
So which one is right for you?
Tirzepatide is the stronger drug on average, so if maximum weight loss is the only variable, that's the answer. It usually isn't the only variable.
What actually decides it:
- How you tolerate the first eight weeks. A drug you can stay on beats a stronger one you quit at week six.
- Your medical history. Thyroid history, pancreatitis, gallbladder disease, and current diabetes medications all narrow the field.
- Cost and supply. These differ between the two and change over time. It's a practical constraint, not a footnote.
- Your target. Someone with 20 pounds to lose and someone with 100 aren't solving the same problem.
- What you've already tried. A poor response to semaglutide is one of the more common reasons to move to tirzepatide.
Frequently Asked Questions
Where to go from here
The honest version of semaglutide vs tirzepatide is that the trial averages favour tirzepatide and your own history decides the rest. That's a conversation with a clinician, not a decision to make from a comparison table.
Start the 2-minute assessment and a licensed clinician will review your information and recommend a starting plan.
Medical disclaimer. This article is for informational purposes only and does not constitute medical advice. GLP-1 medications are prescription-only and require evaluation by a licensed medical provider. Compounded medications are not FDA-approved. Results vary. Always consult a qualified healthcare provider before starting, changing, or stopping any treatment.
