General comparison table
The three most relevant medications in the current landscape of GLP-1 agonists are Mounjaro, Ozempic, and Wegovy. Although they share a similar mechanism of action based on stimulating intestinal hormone receptors, they present significant differences in their composition, approved indications, and documented clinical results.
| Feature | Mounjaro | Ozempic | Wegovy |
|---|---|---|---|
| Active ingredient | Tirzepatide | Semaglutide | Semaglutide |
| Manufacturer | Eli Lilly | Novo Nordisk | Novo Nordisk |
| Mechanism | Dual GIP/GLP-1 agonist | GLP-1 agonist | GLP-1 agonist |
| Primary indication | Type 2 diabetes / Obesity | Type 2 diabetes | Obesity |
| Frequency | Weekly | Weekly | Weekly |
| Maximum dose | 15 mg | 2 mg | 2.4 mg |
| Device | KwikPen (clicks) | FlexTouch (dial) | FlexTouch (dial) |
Dosing comparison
Each of these medications has its own progressive titration schedule. Mounjaro starts at 2.5 mg and escalates in 2.5 mg increments every four weeks until reaching the appropriate therapeutic dose, with a maximum of 15 mg. Ozempic begins with 0.25 mg for four weeks, increases to 0.5 mg for another four weeks, and can reach up to 2 mg. Wegovy also starts at 0.25 mg but has five titration levels that extend over a total of sixteen weeks before reaching the maintenance dose of 2.4 mg.
A notable difference is the administration system. While Ozempic and Wegovy use the FlexTouch device with a rotating dial that visually selects the dose, Mounjaro uses the KwikPen with an audible and tactile click system. The click system allows more precise fractional dosing when the doctor prescribes intermediate personalized doses, something more difficult to achieve with conventional dial devices.
Dual agonist versus single agonist
The fundamental pharmacological difference between Mounjaro and the other medications in this category lies in its dual mechanism of action. While Ozempic and Wegovy act exclusively on GLP-1 receptors, Mounjaro simultaneously activates GIP receptors and GLP-1 receptors. This combined stimulation produces synergistic effects on glucose metabolism, insulin secretion, and appetite regulation that translate into superior clinical results across several parameters measured in clinical trials.
The GIP receptor plays a complementary role to GLP-1 in regulating energy metabolism. When both receptors are activated simultaneously, the effects on satiety, fat oxidation, and insulin sensitivity are mutually enhanced. This is the main reason why direct comparative studies have shown consistent superiority of tirzepatide over semaglutide in both weight reduction and glycemic control.
Clinical trial results
The reference clinical trials provide valuable comparative data. The Mounjaro SURMOUNT program demonstrated an average weight loss of 22.5 percent of body weight with the 15 mg dose over 72 weeks. The Wegovy STEP program recorded an average loss of 14.9 percent with semaglutide 2.4 mg over 68 weeks. In the SURPASS-2 trial, which directly compared tirzepatide with semaglutide 1 mg for type 2 diabetes, Mounjaro demonstrated significantly greater weight reduction at all evaluated doses.
Regarding glycemic control measured by glycated hemoglobin, both medications show clinically significant reductions. Mounjaro achieved average HbA1c reductions of up to 2.3 percentage points with the highest dose, while Ozempic achieved reductions of approximately 1.8 percentage points with semaglutide 2 mg. These differences are statistically significant and clinically relevant for the management of type 2 diabetes.
Comparative table of clinical trial results
To facilitate direct comparison, this table summarizes the most relevant results from the SURMOUNT (tirzepatide) and STEP (semaglutide) research programs regarding weight loss and glycemic control:
| Parameter | Mounjaro 15 mg | Wegovy 2.4 mg | Ozempic 2 mg |
|---|---|---|---|
| Average weight loss | 22.5% | 14.9% | 9.6% |
| Study duration | 72 weeks | 68 weeks | 68 weeks |
| HbA1c reduction | -2.3 pp | N/A (not indicated) | -1.8 pp |
| Trial program | SURMOUNT | STEP | SUSTAIN / SURPASS |
| Patients who lost ≥5% | ~91% | ~86% | ~70% |
| Patients who lost ≥10% | ~79% | ~69% | ~45% |
| Patients who lost ≥20% | ~55% | ~32% | ~15% |
Compared side effect profile
Although all three medications share a predominantly gastrointestinal side effect profile, the incidence and intensity vary. Nausea is the most reported effect with all of them, but tends to be more frequent during the first weeks and during dose increases. Tirzepatide in the SURMOUNT trials showed nausea rates of 24-33% depending on the dose, comparable to those of semaglutide in the STEP trials (around 44% with Wegovy 2.4 mg).
A notable difference is that patients treated with tirzepatide reported severe nausea requiring treatment discontinuation less frequently. The discontinuation rate due to adverse events was 4.3-7.1% in SURMOUNT versus 6.4% in STEP-1. This suggests that, despite the greater potency of the dual agonist, tolerability is comparable or even slightly superior to that of the single agonist.
Both active ingredients have demonstrated cardiovascular benefits in their respective studies. The SELECT study of Wegovy showed a 20% reduction in major cardiovascular events, while the cardiovascular data for tirzepatide from the SURPASS-CVOT study are also confirming a favorable profile. These additional benefits are especially relevant for patients with type 2 diabetes and high cardiovascular risk.
Availability and access in Spain
In Spain, Mounjaro (tirzepatide) is marketed by Eli Lilly and available by prescription since its authorization by the Spanish Agency for Medicines and Health Products (AEMPS). Ozempic and Wegovy, both from Novo Nordisk, are also available by prescription. However, actual pharmacy availability may vary depending on demand and the supply issues that have affected these medications globally.
Regarding public funding, Social Security coverage depends on the indication: for type 2 diabetes, both Mounjaro and Ozempic may be funded, while coverage for the obesity indication varies. It is important to consult with your primary care physician or endocrinologist about the available options and requirements for accessing public funding for these treatments.
Frequently asked questions
Which is better for weight loss?
According to available clinical trials, Mounjaro has demonstrated the greatest average weight loss among currently approved GLP-1 medications, with reductions of up to 22.5 percent of body weight. However, individual response varies, and the most suitable medication for each person depends on multiple factors that should be evaluated by a healthcare professional.
Can I switch from Ozempic to Mounjaro?
Switching between GLP-1 medications is possible and relatively common, but it should always be supervised by your doctor. It is generally recommended to start Mounjaro at the starting dose of 2.5 mg regardless of the previous Ozempic dose, although some doctors may consider starting at higher doses based on the patient's demonstrated tolerance.
Do they have the same side effects?
The side effect profiles are similar among all three medications, with the most frequent being gastrointestinal in nature: nausea, diarrhea, constipation, and vomiting. The incidence may vary slightly between drugs and doses. In general, side effects are more intense during the initial titration phases and tend to decrease with continued use.
Which one is more affordable?
The cost varies significantly depending on the country, the healthcare coverage system, and the availability of generics or biosimilars. In Spain, both Mounjaro and Ozempic are subject to medical prescription and may be partially covered by Social Security when prescribed for type 2 diabetes. For obesity indications, coverage may differ. Consult your doctor and pharmacist about the available funding options.