In this article
If you are comparing semaglutide and tirzepatide, you have probably heard that one works better. The trials do show a difference in average weight loss. But averages are not the whole story, and the two drugs have a lot in common. Here is how they work, what each trial measured, and where they differ.
How semaglutide and tirzepatide work
Your gut releases hormones after you eat. Two of them are GLP-1 (glucagon-like peptide-1) and GIP (glucose-dependent insulinotropic polypeptide). Both help regulate appetite and blood sugar.
Semaglutide is built to mimic GLP-1. Its structure is 94% the same as human GLP-1, and it switches on the GLP-1 receptor [1]. GLP-1 is one of the body's own regulators of appetite and calorie intake, and its receptor is found in brain areas involved in appetite [1].
Tirzepatide switches on two receptors: the GIP receptor and the GLP-1 receptor [2]. The label explains that GLP-1 regulates appetite, and that studies in animals and the lab suggest adding GIP may further help regulate how much you eat [2]. Both receptors are found in brain areas involved in appetite [2].
Both drugs lower calorie intake, most likely by affecting appetite [1, 2]. Both slow down how fast your stomach empties [1, 2]. Both labels say the weight lost is more fat than lean mass [1, 2]. And both stay in your body a long time, which is why they are taken once a week: semaglutide's half-life is about 1 week, and tirzepatide's is about 5 days [1, 2].
| Semaglutide | Tirzepatide | |
|---|---|---|
| Receptors it acts on | GLP-1 | GIP and GLP-1 |
| How it is taken for weight | Weekly injection (a daily tablet also exists) | Weekly injection |
| Starting dose | 0.25 mg weekly for 4 weeks | 2.5 mg weekly for 4 weeks |
| Usual maintenance dose | 2.4 mg weekly (1.7 mg is an option) | 5 mg, 10 mg or 15 mg weekly |
| Half-life | About 1 week | About 5 days |
| Boxed warning | Thyroid C-cell tumors in rodents | Thyroid C-cell tumors in rodents |
How much weight people lost in the main trials
STEP 1: semaglutide
STEP 1 enrolled 1,961 adults with obesity, or overweight plus at least one weight-related health condition, who did not have diabetes [3]. About three in four were women, and the average age was 46 [1]. They took semaglutide 2.4 mg or placebo once a week for 68 weeks, along with a lifestyle program [3].
On average, the semaglutide group lost 14.9% of their body weight. The placebo group lost 2.4% [3]. Half of the semaglutide group (50.5%) lost 15% or more, compared with 4.9% on placebo [3].
SURMOUNT-1: tirzepatide
SURMOUNT-1 enrolled 2,539 adults with obesity, or overweight plus a weight-related condition, without diabetes [4]. About two-thirds were women, and the average age was 45 [2]. They took tirzepatide 5 mg, 10 mg or 15 mg, or placebo, once a week for 72 weeks [4].
Average weight loss was 15.0% on 5 mg, 19.5% on 10 mg and 20.9% on 15 mg, compared with 3.1% on placebo [4]. On the 15 mg dose, 57% of people lost 20% or more of their weight, compared with 3% on placebo [4].
These were separate trials, run at different times with different people and slightly different lengths. Comparing their numbers directly can mislead. That is why a head-to-head trial matters.
The head-to-head trial: SURMOUNT-5
SURMOUNT-5 put the two drugs side by side. It enrolled 751 adults with obesity but without type 2 diabetes [5]. Each person was randomly assigned to the highest dose they could tolerate of either tirzepatide (10 mg or 15 mg) or semaglutide (1.7 mg or 2.4 mg), injected once a week for 72 weeks [5].
At week 72, the tirzepatide group had lost 20.2% of their body weight on average. The semaglutide group had lost 13.7% [5]. Waists shrank by 18.4 cm (about 7 inches) on tirzepatide and 13.0 cm (about 5 inches) on semaglutide [5]. People on tirzepatide were also more likely to reach the 10%, 15%, 20% and 25% weight-loss marks [5].
Two things are worth knowing about this trial. It was open-label, which means participants and their doctors knew which drug they were taking [5]. And it was funded by Eli Lilly, the company that makes tirzepatide [5]. Neither fact makes the result wrong, but both are part of reading it honestly.
An average is also not a prediction for you. In every one of these trials, some people lost much more than the average and some lost much less.
Side effects: more alike than different
In SURMOUNT-5, the most common side effects in both groups were digestive. Most were mild to moderate, and they happened mainly while the dose was being raised [5].
| Side effect | Semaglutide 2.4 mg vs placebo | Tirzepatide 15 mg vs placebo |
|---|---|---|
| Nausea | 44% vs 16% | 28% vs 8% |
| Diarrhea | 30% vs 16% | 23% vs 8% |
| Vomiting | 24% vs 6% | 13% vs 2% |
| Constipation | 24% vs 11% | 11% vs 5% |
Both labels say that side-effect rates from one drug's trials cannot be directly compared with rates from another drug's trials [1, 2]. So treat the table as a picture of what is common, not as a ranking.
The serious warnings are close to identical. Both carry a boxed warning: each drug caused thyroid C-cell tumors in rodents, and it is not known whether that happens in people [1, 2]. Neither should be used if you or a family member has had medullary thyroid carcinoma, or if you have a condition called MEN 2 [1, 2]. Both labels also warn about pancreatitis, gallbladder problems, kidney injury from dehydration, serious allergic reactions, and food in the lungs during anesthesia [1, 2].
One difference matters to some women in perimenopause. The tirzepatide label says it may make birth control pills less effective. It advises switching to a non-oral method, or adding a barrier method, for 4 weeks after starting and for 4 weeks after each dose increase [2].
For the full list for each drug, see semaglutide side effects and tirzepatide side effects.
Dosing schedules
Both drugs start at a low dose and step up slowly. The labels say this is to reduce the risk of digestive side effects [1, 2].
- Semaglutide: 0.25 mg once a week for 4 weeks, then 0.5 mg, 1 mg and 1.7 mg, each for 4 weeks. The usual maintenance dose is 2.4 mg weekly, with 1.7 mg as an option [1]. The label now allows a 7.2 mg weekly dose for some adults who have tolerated 2.4 mg for at least 4 weeks [1]. If a step does not sit well, the label says to consider waiting another 4 weeks before going up [1].
- Tirzepatide: 2.5 mg once a week for 4 weeks. Then 5 mg, rising by 2.5 mg at a time after at least 4 weeks on each dose. Maintenance is 5 mg, 10 mg or 15 mg weekly, and 15 mg is the maximum [2]. The 2.5 mg dose is only for getting started [2].
Missed doses work a little differently. For semaglutide, take a missed dose as soon as you can if your next dose is more than 2 days away; otherwise skip it [1]. For tirzepatide, take it within 4 days (96 hours) of the missed dose; after that, skip it [2]. Either way, go back to your usual day.
Semaglutide also comes as a daily tablet. We compare the two forms in semaglutide pill vs injection.
Which one is right for you?
On average weight loss, tirzepatide came out ahead in the one head-to-head trial [5]. But choosing a medicine is about more than an average. A clinician will weigh your health history, other medicines you take, how you handle side effects, your goals, and cost.
Some people start on one, have trouble with side effects, and do better on the other. Some reach their goal on a lower dose. Neither drug replaces strength training and enough protein, which help protect muscle while the weight comes off. Our article on muscle loss on semaglutide and tirzepatide covers that.
WarriorBabe Health offers semaglutide injections and tirzepatide injections, prescribed by licensed clinicians. Ours are compounded by a licensed pharmacy and are not FDA-approved. The FDA notes that it does not review compounded drugs for safety, effectiveness or quality before they are sold [6]. The trial results in this article come from the FDA-approved products. Ask your clinician which option suits you.
Frequently asked questions
Is tirzepatide stronger than semaglutide?
In the SURMOUNT-5 trial, people on tirzepatide lost more weight on average over 72 weeks: 20.2% compared with 13.7% on semaglutide [5]. That is an average. Your own result can be higher or lower on either drug.
Which has fewer side effects, semaglutide or tirzepatide?
Both most commonly cause nausea, diarrhea, vomiting and constipation, mostly while the dose is going up [1, 2, 5]. The labels warn that side-effect rates from separate trials cannot be compared directly [1, 2]. In SURMOUNT-5, digestive effects were the most common in both groups and were mostly mild to moderate [5].
Can I switch from semaglutide to tirzepatide?
Switching is a clinician's call. Both labels say not to use these drugs together, or with any other GLP-1 medicine [1, 2]. If you switch, your clinician will decide the starting dose and schedule.
References
- Novo Nordisk. Wegovy (semaglutide) injection and tablets, prescribing information. DailyMed, US National Library of Medicine. Revised 6/2026. dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=ee06186f-2aa3-4990-a760-757579d8f77b
- Eli Lilly and Company. Zepbound (tirzepatide) injection, prescribing information. DailyMed, US National Library of Medicine. Revised 8/2026. dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=487cd7e7-434c-4925-99fa-aa80b1cc776b
- Wilding JPH, Batterham RL, Calanna S, et al. Once-weekly semaglutide in adults with overweight or obesity. N Engl J Med. 2021;384(11):989-1002. pubmed.ncbi.nlm.nih.gov/33567185/
- Jastreboff AM, Aronne LJ, Ahmad NN, et al. Tirzepatide once weekly for the treatment of obesity. N Engl J Med. 2022;387(3):205-216. pubmed.ncbi.nlm.nih.gov/35658024/
- Aronne LJ, Horn DB, le Roux CW, et al. Tirzepatide as compared with semaglutide for the treatment of obesity. N Engl J Med. 2025;393(1):26-36. pubmed.ncbi.nlm.nih.gov/40353578/
- US Food and Drug Administration. FDA's concerns with unapproved GLP-1 drugs used for weight loss. www.fda.gov/drugs/drug-alerts-and-statements/fdas-concerns-unapproved-glp-1-drugs-used-weight-loss
This article is for general information. It is not medical advice and does not replace a visit with a licensed clinician who knows your history. Do not start, stop or change a medication without talking to your clinician. If you think you are having a medical emergency, call 911.
