Mounjaro vs Wegovy: detailed comparison of side effects and results
May 11
Medical review: Dr. Anna Lindström, specialist doctor in endocrinology and metabolic diseases
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Two injectable drugs currently dominate the discussion about drug-treated weight loss in Sweden: tirzepatid (Mounjaro) and semaglutide (Wegovy). Both belong to the class of incretin-based drugs and are given as weekly subcutaneous injections — but they work in slightly different ways, produce different results in clinical trials, and have different side effect profiles. This review systematically compares them based on published data, so you can have an informed conversation with your doctor.
| Parameter | Mounjaro (tirzepatid) | Wegoview (semaglutide) |
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|Mechanism of action|Dual GIP/GLP-1 agonist|Selective GLP-1 agonist|
|Weight loss (medium, clinical study)|~20–22% of body weight|~15–17% of body weight|
|Starting dose → maximum dose|2.5 mg → 15 mg/week|0.25 mg → 2.4 mg/week|
|Most common side effects|Nausea, diarrhea, vomiting|Nausea, constipation, vomiting|
|Registration in Sweden|Approved for T2DM, EMA approved for obesity in 2024|Approved for obesity and overweight with risk factors|
|Approximate monthly cost (SEK)| 2 500–4 000 | 2 000–3 500 |
Note: Always consult a doctor before starting or changing treatment with these medicines. The table above is an indicative summary — individual conditions determine which preparation is suitable.
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Tirzepatid: dual action that sets Mounjaro apart from the crowd
Tirzepatid activates two receptors simultaneously and produces, on average, greater weight loss than established GLP-1 drugs.
Tirzepatide is the active substance in Mounjaro and acts as a dual GIP/GLP-1 agonist — that is, it activates both the glucagon-like peptide-1 receptor and the glucose insulinotropic peptide receptor. The combined effect provides stronger insulin release, better glucagon suppression and stronger satiety signaling compared to pure GLP-1 stimulation.
The SURMOUNT studies: what the clinical data actually show
SURMOUNT-1 (New England Journal of Medicine, 2022, n=2,539) is the pivotal study for tirzepatide in obesity. After 72 weeks, participants without type 2 diabetes achieved an average weight loss of 20.9% of body weight with the 15 mg dose, compared to 3.1% in the placebo group. SURMOUNT-2 (2023, n=938), which included people with type 2 diabetes, showed a 15.7% weight loss with the maximum dose — a result that is unusually high for that patient group.
The escalation schedule is important to understand: treatment starts at 2.5 mg per week and is increased by 2.5 mg every four weeks until a tolerated maintenance dose (7.5, 10, 12.5 or 15 mg). Faster escalation correlates with more gastrointestinal side effects without better long-term weight outcomes, which treating physicians should consider.
Mounjaro side effects: what to expect
The side effect profile is similar to other GLP-1-based drugs but has a couple of special features. Diarrhea is reported more frequently with tirzepatide than with semaglutide — in SURMOUNT-1, 17-22% of participants experienced diarrhea, compared to nausea peaking at 31% in the 15 mg group. The side effects are strongest during the escalation phase and subside for most within 4–8 weeks. Reported cases of gastroparesis (delayed gastric emptying) are rare but clinically relevant in preoperative planning — the anesthesia team should always be informed.
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Semaglutide: proven effect with a strong evidence base
Wegovy has longer clinical follow-up and a broad evidence base, including cardiovascular outcome data.
Semaglutide, the substance in Wegovy, is a selective GLP-1 receptor agonist with 94% structural similarity to human GLP-1. The extended half-life (~1 week) allows for once weekly dosing. Compared to tirzepatide, semaglutide lacks GIP agonism, but the clinical effect is still substantial.
The STEP program and cardiovascular data from SELECT
The STEP-1 study (New England Journal of Medicine, 2021, n=1,961) showed 14.9% weight loss after 68 weeks with 2.4 mg semaglutide in non-diabetic subjects. STEP-2 (n=1,210, type 2 diabetes) produced 9.6% weight loss. The SELECT trial (2023, n=17,604) provided conclusive data: in patients with established CVD but without diabetes, semaglutide reduced the risk of major cardiovascular events by 20% compared to placebo. It is a unique evidence support that tirzepatid still lacks for the indication obesity.
Wegovy results in practice and side effect profile
Constipation is more frequent with semaglutide than with tirzepatide — a difference that has clinical significance for patients with pre-existing bowel problems. Nausea and vomiting occur in 20–44% during escalation. The starting dose is 0.25 mg per week for four weeks, then 0.5 mg, and gradually up to the target dose of 2.4 mg over approximately 16 weeks.
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Nausea and vomiting: most common in the first 12 weeks, often relieved by slower de-escalation
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Constipation: affects 24% in STEP-1, may require dietary adjustments or bulking agents
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Gallstone disease: small but real risk increase, especially with rapid weight loss
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Pancreatitis: rare but serious — abdominal pain radiating to the back requires immediate medical attention
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Thyroid cancer: contraindication in case of personal or family history of medullary thyroid cancer
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Weight loss comparison: tirzepatid vs semaglutide in direct analyses
Tirzepatid consistently produces greater weight loss in available data, but evidence-based head-to-head comparisons are still scarce.
To date, no randomized controlled trial has compared tirzepatid and semaglutide head to head for the indication of obesity in a blinded design. However, there are SURPASS-3 (2021) and SURPASS-6 (2023) which compared the drugs in type 2 diabetes with semaglutide 1 mg — not 2.4 mg — as the comparison arm. Tirzepatid was shown to be superior in these studies, but the doses were not equipotent, which limits the conclusions.
An indirect network meta-analysis published in Obesity Reviews (2023) pooled data from 22 studies and 19,000 participants. The result showed that tirzepatide 15 mg was associated with 4–6 percentage points greater weight loss than semaglutide 2.4 mg. It is a statistically and clinically significant difference, but should be interpreted with caution because the study populations are not identical.
| Study | Substance | Population | Weight loss |
|---|
|SURMOUNT-1 (2022)|Tirzepatid 15 mg|Obesity, not T2DM| 20,9 % |
|STEP-1 (2021)|Semaglutide 2.4 mg|Obesity, not T2DM| 14,9 % |
|SURMOUNT-2 (2023)|Tirzepatid 15 mg|Obesity + T2DM| 15,7 % |
|STEP-2 (2021)|Semaglutide 2.4 mg|Obesity + T2DM| 9,6 % |
|SELECT (2023)|Semaglutide 2.4 mg|Cardiovascular disease|9.4% + –20% MACE|
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When Mounjaro fits better — and when Wegovy is the right choice
The choice depends on your disease profile, cardiovascular risk, sensitivity to side effects and access via your region.
None of the drugs are universally superior. The choice should always be made together with a doctor who knows you as a whole.
Situations where tirzepatid may be first choice
Tirzepatid is often a strong alternative if you have type 2 diabetes and need strong glycemic control in parallel with weight loss — precisely the GIP/GLP-1 combination provides a synergistic effect on HbA1c, which in the SURPASS program lowered HbA1c by up to 2.4 percentage points. If you have tried semaglutide without sufficient effect and tolerate gastrointestinal side effects, escalation to tirzepatide may provide further weight reduction. Please note that availability via Swedish county councils varies and that a diabetes diagnosis may be required for subsidy.
Situations where semaglutide may be first choice
Wegovy is the first choice if you have established cardiovascular disease and meet the requirements of the SELECT population — it is the only obesity drug with a proven cardiovascular protective effect in a randomized trial. Semaglutide also has longer clinical experience, more data on long-term effects and, in some regions, is more available through the benefits system. If constipation is a concern and you already have sluggish bowels, tirzepatide should be considered as an alternative, as diarrhea is more frequent there.
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Important: All treatment with Mounjaro or Wegovy must be initiated and followed up by a doctor. Self-medication, dose adjustment without advice or purchases through unsafe channels entail serious health risks. Contact your health centre, an endocrinologist or a specialized obesity clinic for an individual assessment.
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Frequently asked questions about Mounjaro and Wegovy
Can you switch from Wegovy to Mounjaro?
Replacement is possible but must be done under medical instructions. A withdrawal period is rarely needed because the substances have a similar mechanism of action, but the titration schedule for tirzepatid restarts from the starting dose. The effect of the change is usually evaluated after 12–16 weeks.
How quickly do you notice a difference in weight?
Most people see the first pounds disappear within 4-8 weeks. Maximum effect is reached after 52–72 weeks in clinical studies. Tirzepatid often produces a faster initial effect at higher doses, but individual variation is large and dietary patterns significantly affect the result.
What happens if you stop taking the medicine?
Studies show that a large proportion of lost weight returns within 1–2 years if treatment is terminated without lifestyle changes. The STEP-4 trial showed that participants who stopped taking semaglutide regained an average of two-thirds of the weight lost within 52 weeks. Similar data exist for tirzepatide.
Are these medicines suitable during pregnancy?
No. Both are contraindicated during pregnancy and breastfeeding. Effective contraception is recommended during treatment. If pregnancy is planned, the drug should be discontinued in good time — at least 2 months for semaglutide due to its long half-life.
Do Swedish insurances and county councils cover the costs?
Subsidy varies between regions and depends on diagnosis. Wegovy is included in the drug benefit for patients with BMI ≥30 (or ≥27 with risk factors) since 2023. Mounjaro is currently subsidized primarily for type 2 diabetes. Check with your county council and your doctor about current benefit decisions, as this is constantly changing.
Do the drugs work without dietary changes?
Technically speaking, they provide weight loss even without dietary changes, but the effect is significantly lower. In clinical studies, medication was always combined with reduced energy intake and increased physical activity. Treating physicians usually recommend the support of a dietician during the treatment period for the best long-term outcome.
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