MedConsult · Weight loss · Wegovy vs Mounjaro
Both available · Thonglor from 7am · Silom from 8am · every day
Wegovy vs Mounjaro: What the Clinical Trials Actually Show
The quick answer
- More weight loss — tirzepatide (Mounjaro), in every trial that has compared them.
- Proven heart protection — semaglutide (Wegovy), which has the completed outcomes trial.
- Side effects — similar in kind, mostly stomach-related and mostly early.
- Both are available at MedConsult Thonglor and Silom, and you can talk through which fits your history in a weight loss consultation.
Head to head
20.2% vs 13.7%
Average loss over 72 weeks
Heart outcomes
6.5% vs 8.0%
Events on semaglutide vs placebo
Evidence base
Four major trials
22,855 participants in total
The four trials on this page
- STEP 1 — semaglutide against placebo
- SURMOUNT-1 — tirzepatide against placebo
- SURMOUNT-5 — the two medications, head to head
- SELECT — semaglutide and heart outcomes
Where the effect comes from
Why these medications work
Most people who start one of these medications describe the same thing first, and it has nothing to do with the scale. The constant background hum about food goes quiet. The 3pm thought about what is in the office fridge simply stops arriving. There is a name for the hum now — food noise — and for people who have lived with it for twenty years, its absence is the more startling change.
That happens because semaglutide and tirzepatide act on appetite signalling in the brain rather than only on the stomach. Both mimic gut hormones released after eating, which slows how quickly the stomach empties and, more importantly, reaches the parts of the brain that set hunger and reward. Tirzepatide acts on two of those hormone pathways where semaglutide acts on one. Whether that dual action explains the difference in results is still being worked out.
The rest of this page compares the two using the four major trials, all published in the New England Journal of Medicine.
Wegovy (semaglutide): the STEP 1 trial
STEP 1 is the trial that established semaglutide as a weight-loss medication. It enrolled about 1,961 adults with obesity and without diabetes, randomised to weekly semaglutide 2.4 mg or placebo for 68 weeks. Everyone in both groups also received diet and activity counselling, which matters when reading the placebo figure.1
Average weight loss was 14.9% on semaglutide against 2.4% on placebo. For an adult starting at 95 kg, that is roughly 14 kg over sixteen months.
The most common side effects were nausea and diarrhoea. Both appeared mostly in the early weeks, while the dose was still climbing, and were mostly mild to moderate. A small number of participants stopped the medication because of them.
This is the trial behind Wegovy's approval for weight loss in most countries, and it is the benchmark every later trial has been measured against.
STEP 1 at a glance
- Participants
- 1,961 adults
- Dose
- 2.4 mg weekly
- Duration
- 68 weeks
- Average weight loss
- 14.9%
Mounjaro (tirzepatide): the SURMOUNT-1 trial
SURMOUNT-1 did the same job for tirzepatide. It enrolled about 2,539 adults with obesity and without diabetes, randomised to weekly tirzepatide at 5 mg, 10 mg or 15 mg, or to placebo, for 72 weeks.2
Average weight loss came out at around 15% on 5 mg, 19.5% on 10 mg and 20.9% on 15 mg, against about 3% on placebo. The dose response is the striking part: the figure keeps climbing as the dose does, which is not true of every medication in this class.
Side effects were similar in kind to semaglutide's — mainly gastrointestinal, mainly nausea, diarrhoea and constipation, and again concentrated in the period when the dose is being increased.
Read alongside STEP 1, the two trials suggest tirzepatide produces more weight loss. They were separate studies with separate populations, though, so a direct comparison had to wait for a trial that put the two medications in the same room.
SURMOUNT-1 at a glance
- Participants
- 2,539 adults
- Doses
- 5 · 10 · 15 mg weekly
- Duration
- 72 weeks
- Average weight loss, 15 mg
- 20.9%
Head to head: the SURMOUNT-5 trial
SURMOUNT-5 is the only large trial to have given the two medications to comparable people at the same time. 751 adults with obesity and without diabetes were randomised one-to-one to the highest tolerated dose of either tirzepatide or semaglutide, for 72 weeks.3
Average weight loss was 20.2% on tirzepatide against 13.7% on semaglutide. Waist circumference fell further on tirzepatide as well. And at every milestone the trial measured — 10%, 15%, 20% and 25% of body weight — more people on tirzepatide got there.
Two things to know about this trial
It was open-label. Participants knew which of the two medications they were taking. In a trial where the outcome depends partly on eating behaviour, knowing you are on the medication with the bigger reputation can affect the result. A blinded trial would settle that; this one cannot.
It was funded by Eli Lilly, which makes tirzepatide. Industry funding does not make a result wrong, and the trial was published in the New England Journal of Medicine after peer review. It is a fact worth having when you read the headline.
With both of those on the table: both medications produced clinically meaningful weight loss. A 13.7% average is a substantial result by any earlier standard. The trial shows one medication did more, and it does not show the other failed.
| Trial | What it compared | Participants | Duration | Average weight loss |
|---|---|---|---|---|
| STEP 1 | Semaglutide 2.4 mg vs placebo | 1,961 | 68 weeks | 14.9% vs 2.4% |
| SURMOUNT-1 | Tirzepatide 5 / 10 / 15 mg vs placebo | 2,539 | 72 weeks | 15% · 19.5% · 20.9% vs 3% |
| SURMOUNT-5 | Tirzepatide vs semaglutide | 751 | 72 weeks | 20.2% vs 13.7% |
| SELECT | Semaglutide vs placebo, heart outcomes | 17,604 | 3+ years | 6.5% vs 8.0% event rate |
The heart question: the SELECT trial
Weight loss is the visible outcome. What a cardiologist wants to know is whether the medication prevents heart attacks, and only one of these two has an answer.
SELECT enrolled 17,604 adults with overweight or obesity and existing cardiovascular disease, without diabetes, and randomised them to semaglutide 2.4 mg or placebo. It followed them for over three years, which makes it by far the longest and largest trial on this page.4
Heart attack, stroke or cardiovascular death occurred in 6.5% of the semaglutide group against 8.0% on placebo — about a 20% relative reduction. In a population that had already had a cardiac event, that is the kind of result that changes prescribing.
There is no equivalent completed outcomes trial for tirzepatide in this population yet. Studies are running. Until one reports, this is a straightforward point in semaglutide's favour for anyone with established heart disease or high cardiovascular risk, and it is the single reason the more effective weight-loss medication is not automatically the better choice.
Which one is right for you
The trials narrow it to a handful of situations. Most people can work out which one they are in before they ever walk into a clinic.
If the number you want is large
Tirzepatide's extra loss is worth more to you. At a higher starting weight, or with a goal of 20% or more, the gap between 20.2% and 13.7% stops being academic. On a 110 kg starting weight it is about seven kilograms of difference.
If you have heart disease
Semaglutide has the outcome evidence. A previous heart attack or stroke, established cardiovascular disease, or a high calculated risk all point the same way: SELECT tested exactly that population and found fewer events. The weight loss is smaller and the second benefit is proven.
If side effects are the worry
The profiles are similar enough that this rarely decides it. Both are mainly gastrointestinal, both are worst early, and both are started at a low dose and increased gradually so the stomach has time to settle. Individual tolerance varies more than the two medications do.
If you have taken one already
Your own experience outranks any trial average. How you tolerated a previous medication, what other medications you take, your thyroid and blood sugar, and your family history all shift the answer away from the population figure. That is the whole substance of the first appointment.
MedConsult stocks both. You can bring your own reading to a weight loss consultation at either branch, ask which fits your history, and decide from there. If you would rather start with a general appointment and no medication in the conversation at all, a GP consultation does that.
Both medications, either branch
Talk to a doctor about which fits your history.
One appointment covers your history, the baseline bloods and an honest comparison of the two, with the trial figures on the table.
What to expect at MedConsult
The first appointment is a conversation and a set of measurements. You go through your weight history, what you have tried, any other conditions and the medications you take. Baseline checks follow — blood pressure, thyroid, fasting glucose and HbA1c, lipids — either on the day or through a health check-up.
If you go ahead with medication, you are shown how to give the injection yourself, once a week, at the lowest dose. Follow-up appointments look at how you are tolerating it and whether the dose moves up. Most of those are short.
Both branches run the same service in English. Full detail of what the assessment covers is on the weight loss page, and you can walk in at either — Thonglor from 7am, Silom from 8am, every day.
Book a weight loss consultation
Talk to a doctor about which fits your history.
Both medications are available at both branches. Walk in from 7am at Thonglor, 8am at Silom, every day.
Frequently asked questions
Is Mounjaro better than Wegovy for weight loss?
For weight loss alone, the trial evidence favours it. In SURMOUNT-5, which gave the two medications to comparable people over 72 weeks, average loss was 20.2% on tirzepatide against 13.7% on semaglutide. Semaglutide still has the heart-outcomes data that tirzepatide currently lacks, so “better” depends on what you are trying to fix.
Which is safer, Wegovy or Mounjaro?
The side-effect profiles are similar in kind. Both are mainly gastrointestinal — nausea, diarrhoea, constipation — and both are worst in the early weeks while the dose is climbing. No trial has shown one to be clearly safer than the other. Semaglutide has three years of cardiovascular follow-up behind it, which is a longer safety record rather than a better one.
Can I switch from Wegovy to Mounjaro, or the other way?
Switching is common and it is done at the low starting dose of the new medication rather than at the equivalent of your old one, because the two are not dose-for-dose interchangeable. Your tolerance of the first medication is useful information when choosing the second, so bring the detail of what you took and how it went.
Are Wegovy and Mounjaro available in Thailand?
Both are available in Thailand on prescription, and MedConsult stocks both at Thonglor and Silom. Supply of these medications has fluctuated globally since 2023, so it is worth asking about current availability of a specific dose when you book.
How long do I need to stay on the medication?
These are treatments for a long-term condition rather than a course with an end date. Trials show weight returns for most people after stopping, because the appetite signalling goes back to how it was. How long you continue is something you decide at follow-up, with your results and your tolerance in front of you.
Do I need to have diabetes to be prescribed these?
No. All four trials on this page enrolled adults with obesity or overweight and without diabetes, which is exactly the population these medications were studied in for weight loss. Whether either suits you depends on your weight, your health history and any other medications you take.
Medically reviewed
Medically reviewed by Dr. Donna Robinson · 3 September 2026
Published 3 September 2026 · Last updated 3 September 2026
Thai Medical Licence 23692 · UK Medical Licence 2613093
Reviewed again every six months, or when the trial evidence changes
References
- 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. doi:10.1056/NEJMoa2032183
- 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. doi:10.1056/NEJMoa2206038
- 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. doi:10.1056/NEJMoa2416394
- Lincoff AM, Brown-Frandsen K, Colhoun HM, et al. Semaglutide and cardiovascular outcomes in obesity without diabetes. N Engl J Med. 2023;389(24):2221-2232. doi:10.1056/NEJMoa2307563
Peer-reviewed primary sources only. We do not cite other clinics.
Where to read next
Weight loss at MedConsult — what the assessment coversHow much weight can I lose in a month? — what a realistic rate of loss looks like.
This article is for general information and does not replace an individual medical assessment. Results vary between individuals. · Thonglor 7:00–19:00 · Silom 8:00–19:00 · every day
Which branch?
Book a weight loss consultation.
Thonglor 7:00–19:00 · Silom 8:00–19:00 · every day