Mounjaro (tirzepatide): trials, side effects and approved dosing
In short
Tirzepatide is a peptide medicine acting on GLP-1 and GIP receptors that holds an EU marketing authorisation as Mounjaro for type 2 diabetes and weight management [4]regulator. Its effects have been tested in large randomised human trials [1, 2]A.
- Mounjaro (tirzepatide) is a prescription medicine injected under the skin once a week [4]regulator.
- In SURMOUNT-1 body weight fell over 72 weeks by a mean of 15.0% to 20.9% depending on the dose, against 3.1% with placebo [1]A.
- In a head-to-head trial weight fell more with tirzepatide than with semaglutide (20.2% and 13.7%), but the trial was open-label and manufacturer-funded [8]A.
- Weakness: when the medicine was stopped, much of the weight came back, and the most common side effects are nausea, diarrhoea and other stomach symptoms [1, 9]A.
- Tirzepatide is listed in Annex 1 of Fimea's medicines list, and Annex 1 substances are controlled as medicines in Finland [7]regulator. According to WADA the status of GLP-1 drugs is unchanged on the 2027 Prohibited List [14]regulator.
What is tirzepatide (Mounjaro)?
Tirzepatide is a prescription medicine that acts in the body like two gut hormones: GLP-1 (glucagon-like peptide 1) and GIP (glucose-dependent insulinotropic polypeptide). According to the EMA, these hormones bind to receptors in the pancreas and the brain, among other places [4]regulator.
The medicine is injected under the skin once a week with a prefilled pen. In the EU it is sold under the brand name Mounjaro [4]regulator. In the United States the same substance is sold as Mounjaro for diabetes and as Zepbound for weight management [5]regulator.
Tirzepatide is a different substance from semaglutide, the active substance in Ozempic and Wegovy, which acts only on the GLP-1 receptor [2]A [4]regulator. All GLP-1 drugs compared: Weight-loss drugs (GLP-1). All substances: Peptides A-Z.
Evidence at a glance
Each cell gives the kind of study and its source. The letter is the evidence level, not the result.
| Claimed effect | Humans | Animals | Cells |
|---|---|---|---|
| Weight loss (no diabetes) | 2,539 adults, 72 weeks: weight fell 15.0% to 20.9%, 3.1% with placebo [1]A | - | - |
| Blood glucose (type 2 diabetes) | 1,879 people with diabetes, 40 weeks: HbA1c fell more than with semaglutide 1 mg [2]A | - | - |
| Cardiovascular events | 13,165 patients: not worse than dulaglutide, superiority not shown [3]A | - | - |
| Compared with semaglutide (obesity) | 751 adults, 72 weeks: weight fell 20.2% and 13.7%, open-label [8]A | - | - |
| Keeping weight off after stopping | Those switched to placebo regained 14.0% over 52 weeks [9]A | - | - |
| Thyroid C-cell tumours | Not known whether this applies to humans [5]regulator | C-cell tumours seen in rats [5]regulator | - |
| Safety | Most common harms are stomach symptoms; 4.3% to 7.1% stopped treatment (placebo 2.6%) [1]A [10]official | - | - |
"-" = no such study is known.
What is tirzepatide used for?
Tirzepatide is used for type 2 diabetes and for weight management. Mounjaro received an EU-wide marketing authorisation on 15 September 2022 [4]regulator.
- Type 2 diabetes: adults, and children and adolescents aged 10 and above [4]regulator.
- Weight management: adults with a BMI of 30 or more, or 27 to 30 together with a weight-related health problem [4]regulator.
Mounjaro is available only with a prescription [4]regulator. Cost, reimbursement by Kela (Finland's social insurance institution) and how to get a prescription: Weight-loss drug cost and prescription.
How does tirzepatide work?
Tirzepatide acts on both GLP-1 and GIP receptors. According to the EMA, this increases the insulin released after a meal and reduces appetite [4]regulator.
Semaglutide acts only on the GLP-1 receptor [2]A. Acting on two receptors is the main difference between these medicines, but the trials measure the outcome (weight, blood glucose), not which receptor accounts for the difference [2, 8]A.
GLP-1 medicines slow down emptying of the stomach [13]regulator. That is why the doctor must be told about the medicine before anaesthesia, see Interactions.
Has tirzepatide been studied in humans?
Yes, extensively. The phase 3 trials covered on this page enrolled more than 17,000 participants in total [1, 2, 3]A. This sets tirzepatide apart from most substances on this site, which have mainly animal studies.
Weight management: SURMOUNT-1
2,539 adults with obesity, or overweight plus a weight-related condition, but without diabetes received tirzepatide or placebo for 72 weeks. Body weight fell by a mean of 15.0% (5 mg), 19.5% (10 mg) and 20.9% (15 mg), against 3.1% with placebo [1]A.
A weight loss of at least 5% was reached by 85% to 91% of those on tirzepatide and 35% of those on placebo. A loss of at least 20% was reached by 50% (10 mg) and 57% (15 mg), against 3% with placebo [1]A.
Type 2 diabetes: SURPASS-2
1,879 people with type 2 diabetes received tirzepatide or semaglutide 1 mg for 40 weeks. The long-term blood glucose marker HbA1c fell by 2.01 to 2.30 percentage points with tirzepatide and 1.86 percentage points with semaglutide. Weight loss was 1.9 to 5.5 kg greater with tirzepatide depending on the dose. The trial was open-label, so participants knew which medicine they received [2]A.
Heart and blood vessels: SURPASS-CVOT
13,165 people with type 2 diabetes and cardiovascular disease received tirzepatide or dulaglutide, another diabetes medicine shown to reduce cardiovascular events. Cardiovascular death, heart attack or stroke occurred in 12.2% of the tirzepatide group and 13.1% of the dulaglutide group. Tirzepatide was not worse, but the difference was not enough to show it was better [3]A.
When the medicine is stopped: SURMOUNT-4 and SURMOUNT-MAINTAIN
In SURMOUNT-4, 670 adults first took tirzepatide for 36 weeks and lost a mean of 20.9% of body weight. They were then randomly assigned to continue tirzepatide or switch to placebo for 52 weeks. Those who continued lost a further 5.5%, while those switched to placebo regained 14.0%. At least 80% of the initial weight loss was kept by 89.5% of those who continued and 16.6% of those switched to placebo [9]A.
In SURMOUNT-MAINTAIN, a dose lowered to 5 mg held weight less well than continuing the maximum tolerated dose: -16.6% and -21.9% from baseline at week 112. According to the researchers, individual responses may vary [11]A.
Who studies tirzepatide?
The large tirzepatide trials were run or funded by the manufacturer, Eli Lilly. SURMOUNT-1, SURPASS-2, SURPASS-CVOT and SURMOUNT-5 were funded by Lilly [1, 2, 3, 8]A, and some authors of SURMOUNT-4 were Lilly employees [9]A. The results are group averages and do not transfer as such to an individual.
Author of this page: the editorial team
This page was written by the Molecular Recovery editorial team. The draft was made with the help of AI, and the claims were checked against the sources (AI policy). The page has not been medically reviewed. How we work: About us.
What are the side effects of tirzepatide?
The most common side effects are stomach symptoms. According to the EMA, the most common side effects of Mounjaro (in more than 1 in 10 people) are nausea, vomiting, abdominal pain, constipation and diarrhoea, and low blood glucose when used with a sulphonylurea or insulin [4]regulator.
What users report. In the Reddit accounts we compiled (not research), 103 of 211 people (49%) reported some harm, most often: nausea (37, 18%), burping (14, 7%), food aversion or eating too little (11, 5%), constipation (11, 5%) and diarrhoea (11, 5%). People tend to post when something goes wrong, so this share does not tell how common harms are. Tirzepatide is a prescription medicine. The figures describe users' experiences, not treatment advice: we did not record doses, dose changes, where the medicine came from or how much weight was lost. The harms in detail: Tirzepatide user experiences.
What the trials saw
- SURMOUNT-1: stomach symptoms were mostly mild to moderate and occurred mainly while the dose was being raised. Treatment was stopped because of adverse events by 4.3% to 7.1% of the tirzepatide groups and 2.6% of the placebo group [1]A.
- SURPASS-2: nausea occurred in 17% to 22% of those on tirzepatide, diarrhoea in 13% to 16% and vomiting in 6% to 10%. Serious adverse events were reported in 5% to 7% of those on tirzepatide and 3% of those on semaglutide [2]A.
- Product information: in placebo-controlled type 2 diabetes trials, stomach symptoms occurred in 37.1% (5 mg), 39.6% (10 mg) and 43.6% (15 mg), against 20.4% on placebo. 3.0%, 5.4% and 6.6% stopped treatment because of them (placebo 0.4%) [10]official.
Thyroid
According to the FDA, tirzepatide caused thyroid C-cell tumours in rats. It is not known whether it causes them in humans. It is not used in people with a personal or family history of medullary thyroid cancer or with MEN2 syndrome [5]regulator.
Pancreas and gallbladder
According to the summary of product characteristics, acute pancreatitis has been reported in people taking tirzepatide. Patients should know its symptoms: if pancreatitis is suspected the medicine is stopped, and it is not restarted if pancreatitis is confirmed. Acute pancreatitis, gallstones and inflammation of the gallbladder are uncommon side effects (1 to 10 in 1,000 users) [10]official.
In the placebo-controlled weight management trials, acute gallbladder problems occurred in 2.0% of people on tirzepatide and 1.6% on placebo, and they were linked with weight loss [10]official.
Products bought online
The safety data apply to the pharmacy medicine. According to the EMA and EU medicines agencies, illegal GLP-1 products sold online may not contain the claimed active substance at all and may contain harmful levels of other substances [12]regulator. More: Side effects and safety.
Interactions and who there is no data for
The main interaction concerns diabetes medicines: with a sulphonylurea or insulin, low blood glucose is one of the most common side effects (more than 1 in 10 people) [4]regulator.
- Anaesthesia and deep sedation: GLP-1 medicines slow down emptying of the stomach. EMA's safety committee could not establish a causal link, but a warning was added to the product information: patients must tell the doctor they take a GLP-1 medicine before a procedure under anaesthesia or deep sedation [13]regulator.
- Medicines taken by mouth: tirzepatide slows stomach emptying and can therefore slow the absorption of medicines taken by mouth, most at the start of treatment. The summary of product characteristics advises monitoring medicines with a narrow safe dose range, such as warfarin and digoxin, especially at the start and after a dose increase [10]official.
- Contraceptive pills: a single dose of tirzepatide lowered blood levels of the hormones in a combined contraceptive pill. According to the EU summary of product characteristics this is not clinically relevant and the pill dose does not need changing [10]official. Women who could become pregnant are recommended to use contraception during treatment [10]official.
- Little data: experience in severe kidney or liver impairment and in people over 85 is limited, and there are no data in children with diabetes weighing under 50 kg [10]official.
- Thyroid: not used in people with a personal or family history of medullary thyroid cancer or with MEN2 syndrome [5]regulator.
Pregnancy and breastfeeding. Tirzepatide is not recommended during pregnancy, because animal studies showed reproductive harm and there are hardly any data from pregnant women. According to the summary of product characteristics it is stopped if pregnancy occurs, and at least one month before a planned pregnancy, because it leaves the body slowly. After a single dose, tirzepatide in breast milk was undetectable or very low, and the summary says use during breastfeeding can be considered [10]official. Discuss them with the prescriber.
What argues against it and what is unknown
The effect is well shown, but durability and the long term are open. When the medicine was stopped, much of the weight came back [9]A.
Counter-evidence
- In SURMOUNT-4, only 16.6% of those switched to placebo kept at least 80% of the initial weight loss [9]A.
- In SURPASS-CVOT, tirzepatide was not worse than dulaglutide for cardiovascular events, but it could not be shown to be better [3]A.
- The head-to-head comparisons with semaglutide (SURPASS-2 and SURMOUNT-5) were open-label and funded by the maker of tirzepatide [2, 8]A.
What the evidence does not support
- "Mounjaro contains the same substance as Ozempic": it does not. Tirzepatide acts on both GIP and GLP-1 receptors, semaglutide only on the GLP-1 receptor [2]A [4]regulator.
- "Once the weight is off, the medicine can be stopped and the result stays": those switched to placebo regained a mean of 14.0% over 52 weeks [9]A.
- "Tirzepatide bought online for research use is the same as Mounjaro from a pharmacy": according to Fimea, "for research use only" means the product is not intended for humans, and an unauthorised product may contain a different substance from the one on the label [6]regulator.
What is unknown
- Whether tirzepatide causes the thyroid C-cell tumours in humans that were seen in rats [5]regulator.
- What the best maintenance dose is: a lowered dose held weight less well, and according to the researchers individual responses may vary [11]A.
- How the difference from semaglutide develops beyond 72 weeks: SURMOUNT-5 lasted 72 weeks [8]A.
Tirzepatide dosage in studies and in the product information
Tirzepatide has an approved dosage, set out in the summary of product characteristics for Mounjaro [10]official. The dose and any change to it are always decided by the prescriber. The figures below show what the product information and the trials say; they are not dosing instructions.
| Step | Who | Dose and route | Duration |
|---|---|---|---|
| Start | both indications | 2.5 mg under the skin once a week | 4 weeks [10]official |
| Escalation | both indications | 5 mg once a week; if needed, increases in 2.5 mg steps | at least 4 weeks on each dose [10]official |
| Maintenance, adults | both indications | 5 mg, 10 mg or 15 mg once a week (maximum 15 mg) | not set [10]official |
| Maintenance, ages 10-17 | type 2 diabetes | 5 mg or 10 mg once a week (maximum 10 mg) | not set [10]official |
| Study | Who | Dose and route | Duration |
|---|---|---|---|
| SURMOUNT-1 | 2,539 adults, obesity or overweight, no diabetes | 5, 10 or 15 mg under the skin once a week; raised to target over 20 weeks | 72 weeks [1]A |
| SURPASS-2 | 1,879 people with type 2 diabetes | 5, 10 or 15 mg once a week | 40 weeks [2]A |
| SURPASS-CVOT | 13,165 people with diabetes and cardiovascular disease | up to 15 mg once a week | event-driven follow-up [3]A |
| SURMOUNT-5 | 751 adults, obesity, no diabetes | maximum tolerated dose 10 or 15 mg once a week | 72 weeks [8]A |
| SURMOUNT-4 | 670 adults, obesity or overweight | maximum tolerated dose 10 or 15 mg once a week | 36 + 52 weeks [9]A |
What the figures do not tell you. A trial dose shows what a group was given, not which dose suits an individual. The best maintenance dose is open [11]A. Product information table and notes: Approved tirzepatide dosing. The dose calculator does not open with tirzepatide preselected, because use of the pharmacy pen is explained in the product information and by the prescriber. The general calculator's list includes tirzepatide only to fill in the vial size of powder sold online; that powder is not Mounjaro, and the pharmacy pen is not mixed with water. Other substances: Dosing.
Mounjaro (tirzepatide) vs Ozempic (semaglutide): what is the difference?
They are different substances: tirzepatide acts on GIP and GLP-1 receptors, semaglutide only on the GLP-1 receptor [2]A [4]regulator. Both are injected once a week [4]regulator [8]A.
- Obesity: in SURMOUNT-5, 751 adults without type 2 diabetes received the maximum tolerated dose of either medicine for 72 weeks (tirzepatide 10 or 15 mg, semaglutide 1.7 or 2.4 mg). Body weight fell by a mean of 20.2% with tirzepatide and 13.7% with semaglutide, and waist circumference by 18.4 cm and 13.0 cm [8]A.
- Type 2 diabetes: in SURPASS-2, tirzepatide lowered HbA1c and weight more than semaglutide 1 mg [2]A.
- Side effects: in both comparisons the most common adverse events were stomach symptoms, mostly mild to moderate [2, 8]A.
- Caveats: both trials were open-label and funded by the maker of tirzepatide, and the results are group averages [2, 8]A.
More on semaglutide: Semaglutide (Ozempic, Wegovy). All GLP-1 drugs: Weight-loss drugs (GLP-1).
Registered trials compare tirzepatide with CagriSema: CagriSema comparison.
Situation in the United States
The US Food and Drug Administration (FDA) approved tirzepatide for weight management under the name Zepbound on 8 November 2023. For diabetes the same substance is sold in the US as Mounjaro [5]regulator.
Is tirzepatide legal in Finland?
Yes, as a prescription medicine. Tirzepatide is a prescription medicine with a marketing authorisation in the EU [4]regulator. It is listed in Annex 1 of Fimea's medicines list (230/2025), and Annex 1 substances are controlled as medicines in Finland, so it is not a supplement or a chemical [7]regulator.
- Prescription. Mounjaro is available only with a prescription [4]regulator. Cost and getting a prescription: Weight-loss drug cost and prescription.
- Fimea warning, 29 June 2026. Fimea warned about injectable peptides sold online and on social media, including products marketed for weight management. According to Fimea, "for research use only" means the product is not intended for humans, and medicines should be bought only from legal pharmacies [6]regulator.
- EU warning, 3 September 2025. The EMA and EU medicines agencies warned of a sharp rise in illegal products marketed as tirzepatide and other GLP-1 medicines. They are often sold via fraudulent websites and promoted on social media, and they are not authorised [12]regulator.
- Import. Ordering medicines from outside the EU is covered on Peptides and the law in Finland. Bringing them back from travel: Travelling with peptides.
This is not legal advice. Disclaimer.
Is tirzepatide doping?
No, tirzepatide is not on the Prohibited List. According to WADA, the status of GLP-1 drugs such as semaglutide and tirzepatide is unchanged on the 2027 Prohibited List, because its expert group found the evidence not yet sufficient for inclusion [14]regulator.
This does not make unapproved peptides permitted. Athletes should check the current list on WADA's website [14]regulator.
FAQ
Ozempic vs Mounjaro: which is more effective?
In the head-to-head SURMOUNT-5 trial, adults with obesity but without diabetes lost a mean of 20.2% of body weight over 72 weeks with tirzepatide and 13.7% with semaglutide [8]A. In type 2 diabetes, tirzepatide lowered blood glucose and weight more than semaglutide 1 mg [2]A. Both trials were open-label and manufacturer-funded, and the results are group averages [2, 8]A.
What is the difference between Mounjaro and Ozempic?
A different active substance. Tirzepatide acts on both GIP and GLP-1 receptors [4]regulator, semaglutide only on the GLP-1 receptor [2]A.
Mounjaro dose: what is the approved dosage?
The prescriber decides the dose. According to the product information the start is 2.5 mg once a week for four weeks, and the maintenance dose in adults is 5, 10 or 15 mg once a week [10]official. More: dosage in studies and in the product information.
Mounjaro side effects: what is reported for tirzepatide?
The most common are nausea, vomiting, diarrhoea, constipation and abdominal pain [1]A [4]regulator. Acute pancreatitis and gallstones are uncommon [10]official. Thyroid C-cell tumours were seen in rats, and the risk in humans is unknown [5]regulator.
Stopping Mounjaro: does the weight come back?
Largely, yes. In SURMOUNT-4, those switched to placebo regained a mean of 14.0% of body weight over 52 weeks, while those who continued tirzepatide lost a further 5.5% [9]A. Talk to your prescriber before stopping.
Mounjaro experiences: what do the trials show?
One person's experience does not show how the medicine works for others. In SURMOUNT-1 body weight fell over 72 weeks by a mean of 15.0% to 20.9% depending on the dose, and 3.1% with placebo [1]A.
What do users themselves report about tirzepatide?
In the Reddit accounts of 211 people we compiled (not research), 165 (78%) reported some benefit and 103 (49%) some harm. The accounts are self-selected and prove neither that it works nor that it is safe: Tirzepatide user experiences.
Mounjaro in Finland: can you get tirzepatide without a prescription?
No. Mounjaro (tirzepatide) is available only with a prescription [4]regulator, and tirzepatide is in Annex 1 of Fimea's medicines list, whose substances are controlled as medicines [7]regulator. Fimea warns against buying injectable peptides online [6]regulator.
Is tirzepatide banned in sport?
It is not on the Prohibited List. According to WADA, the status of GLP-1 drugs is unchanged on the 2027 list [14]regulator.
Read the research yourself: sources
Every source opens the original publication or the regulator's page. The level shows what the source itself reports.
- Jastreboff AM, et al. Tirzepatide Once Weekly for the Treatment of Obesity (SURMOUNT-1). N Engl J Med. 2022;387:205-216. PMID 35658024 A
- Frías JP, et al. Tirzepatide versus Semaglutide Once Weekly in Patients with Type 2 Diabetes (SURPASS-2). N Engl J Med. 2021;385:503-515. PMID 34170647 A
- Nicholls SJ, et al. Cardiovascular Outcomes with Tirzepatide versus Dulaglutide in Type 2 Diabetes (SURPASS-CVOT). N Engl J Med. 2025;393:2409-2420. PMID 41406444 A
- European Medicines Agency. Mounjaro: EPAR summary and authorisation details. EMA regulator
- U.S. Food and Drug Administration. FDA Approves New Medication for Chronic Weight Management (Zepbound), press release, 8 Nov 2023. FDA regulator
- Fimea. Fimea warns: do not use injectable peptides purchased online (29 Jun 2026). Fimea regulator
- Finland. Lääkeluettelo (Fimea medicines list), 230/2025, annex 1. Finlex regulator
- Aronne LJ, et al. Tirzepatide as Compared with Semaglutide for the Treatment of Obesity (SURMOUNT-5). N Engl J Med. 2025;393(1):26-36. PMID 40353578 A
- Aronne LJ, et al. Continued Treatment With Tirzepatide for Maintenance of Weight Reduction in Adults With Obesity: The SURMOUNT-4 Randomized Clinical Trial. JAMA. 2024;331(1):38-48. PMID 38078870 A
- European Medicines Agency. Mounjaro (tirzepatide): EPAR product information, Annex I summary of product characteristics. Last updated 21 Sep 2026. EMA official
- Horn DB, et al. Tirzepatide for maintenance of bodyweight reduction in people with obesity in the USA (SURMOUNT-MAINTAIN): a multicentre, double-blind, randomised, placebo-controlled trial. Lancet. 2026;407(10545):2305-2318. PMID 42119587 A
- European Medicines Agency. Warning about sharp rise in illegal medicines sold in the EU (GLP-1 receptor agonists), news, 3 Sep 2025. EMA regulator
- European Medicines Agency. Meeting highlights from the Pharmacovigilance Risk Assessment Committee (PRAC) 8-11 July 2024 (GLP-1 receptor agonists: aspiration during general anaesthesia or deep sedation). EMA regulator
- World Anti-Doping Agency. WADA publishes 2027 Prohibited List, press release, 21 Sep 2026. WADA regulator
Research sources checked 9-13 Oct 2026. Regulator and registry sources checked 15 Sep to 13 Oct 2026.
Evidence levels: A = randomised human trial or meta-analysis · B = observational human study or case series · C = animal study · D = cell or laboratory study · E = not peer-reviewed · regulator = a regulator's assessment or decision, not research evidence. The marker official means official product information (summary of product characteristics or label); it is not research evidence. For a review, the level shows what kind of research the statement rests on. No level: statements that something has not been studied, reviews' interpretations, named hypotheses and the general rules in our certificate-of-analysis guide.
Content is general information about research, not medical advice. If you have symptoms, contact a healthcare professional.