The drug is from Eli Lilly and is registered in Europe for type 2 diabetes and for weight management in overweight and obesity. In studies, people without diabetes lost an average of up to 20.9% of their body weight in 72 weeks. Tirzepatide is only available by prescription. In this blog, you will read how it works, what the research shows, how it compares to semaglutide (Ozempic and Wegovy), what side effects you can expect, and its reimbursement status in 2026.
How does tirzepatide work?
Tirzepatide is a dual agonist: it activates both the GIP receptor and the GLP-1 receptor. This distinguishes it from semaglutide, which only acts on GLP-1. Both hormones are naturally produced by your gut when you eat; tirzepatide mimics them but works much longer, making one injection per week sufficient.
What it does in your body:
- Less hunger and faster satiety. GLP-1 and GIP send a satiety signal to the brain. Many people also notice less 'food noise', the constant thinking about food.
- Slower gastric emptying. Food stays in your stomach longer, keeping you feeling full for an extended period.
- Better blood sugar regulation. The pancreas produces more insulin when your blood sugar rises, and less glucagon.
- Possible effect on fat metabolism. GIP appears to play a role in how adipose tissue stores energy. Researchers believe this partly explains why tirzepatide works more strongly than drugs that only mimic GLP-1.
Tirzepatide is not a miracle cure. It works best in conjunction with dietary and exercise adjustments, under medical supervision. How much weight do you lose with tirzepatide? What the SURMOUNT studies show In the largest study, SURMOUNT-1, adults with obesity without diabetes lost an average of 15 to 21% of their weight in 72 weeks, compared to 3.1% with placebo. The higher the dose, the greater the effect. All participants also received lifestyle advice.
| Study | Who participated | Duration | Tirzepatide result | Placebo |
|---|---|---|---|---|
| SURMOUNT-1 | 2,539 adults with obesity or overweight, without diabetes | 72 weeks | −15.0% (5 mg), −19.5% (10 mg), −20.9% (15 mg) | −3.1% |
| SURMOUNT-2 | Adults with obesity and type 2 diabetes | 72 weeks | −12.8% (10 mg), −14.7% (15 mg) | −3.2% |
| SURMOUNT-4 | People who continued tirzepatide after 36 weeks OR stopped | 88 weeks | Continuing: another −5.5% | Stopping: 14% regained |
Two things stand out. People with type 2 diabetes lose slightly less weight on average than people without diabetes; this is observed with all drugs in this group. And those who stop regain a significant portion of the weight. Tirzepatide therefore works as long as you use it; a plan for the period thereafter is part of the treatment. In addition to weight loss, the studies also showed improvements in blood pressure, cholesterol, blood sugar, and waist circumference. In the United States, tirzepatide (as Zepbound) has now also been approved for obstructive sleep apnea in obesity.
Tirzepatide vs semaglutide: what's the difference?
In a direct comparison (SURMOUNT-5), people on tirzepatide lost an average of 20.2% of their weight in 72 weeks, compared to 13.7% with semaglutide. Semaglutide is the active ingredient in Ozempic, Wegovy, and the Wegovy pill.
| Tirzepatide | Semaglutide | |
|---|---|---|
| Brand names | Mounjaro (EU), Zepbound (US) | Ozempic, Wegovy, Wegovy pill, Rybelsus |
| Acts on | GIP + GLP-1 | GLP-1 |
| Administration | Injection, 1× per week | Injection 1× per week, or daily tablet |
| Average weight loss in studies | Up to ±21% | Up to ±15% (Wegovy 2.4 mg) |
| Side effects | Mainly gastrointestinal complaints | Mainly gastrointestinal complaints |
More weight loss does not automatically mean tirzepatide is the best choice for everyone. Your medical history, other medications, tolerability, and cost all play a role. Therefore, a doctor will determine with you which medication is suitable. Read more about Wegovy and Mounjaro.
Tirzepatide dosage: how it is built up
Tirzepatide starts at 2.5 mg per week and is increased by 2.5 mg every four weeks up to a maximum of 15 mg. This slow build-up allows your body to adjust and limits gastrointestinal side effects.
| Period | Weekly dose | Goal |
|---|---|---|
| Month 1 | 2.5 mg | Starting dose, adjustment |
| Month 2 | 5 mg | First maintenance dose |
| Month 3 | 7.5 mg | Escalation if needed |
| Month 4 | 10 mg | Maintenance dose |
| Month 5 | 12.5 mg | Escalation if needed |
| Month 6 | 15 mg | Maximum dose |
| Not everyone goes up to 15 mg. If someone is losing weight well at a lower dose, or if the side effects are too bothersome, the doctor will keep them at that dose. You inject the medication once a week subcutaneously into the abdomen, thigh, or upper arm, on a fixed day, with or without a meal. |
Side effects of tirzepatide
Most side effects involve the stomach and intestines and primarily occur in the first few weeks and after each dose increase. They are usually mild to moderate and decrease over time. Common: nausea, diarrhea, constipation, vomiting, decreased appetite, bloating, heartburn, and fatigue. Less common, but important to be aware of: inflammation of the pancreas (persistent, severe abdominal pain that can radiate to the back), gallstones, dehydration due to vomiting or diarrhea, and low blood sugar if you are also using insulin or a sulfonylurea derivative. In such cases, contact a doctor immediately.
**Note with birth control pills: ** tirzepatide can reduce the effectiveness of oral contraceptives. It is advised to use an additional (barrier) method during the first four weeks after starting and after each dose increase.
Who should not use tirzepatide?
Tirzepatide is not suitable if you: • are pregnant, planning to become pregnant, or breastfeeding; • have a history of pancreatitis (always consult a doctor); • have a (family) history of medullary thyroid carcinoma or MEN2 syndrome; • have severe gastrointestinal disease, such as severe gastroparesis; • are younger than 18 years. For weight management, tirzepatide is considered for a BMI of 30 or higher, or from 27 if you also have weight-related conditions such as high blood pressure, type 2 diabetes, or sleep apnea. A doctor will assess whether it is safe for you.
Mounjaro, Zepbound, and tirzepatide: what's in a name?
Tirzepatide is the generic name; Mounjaro and Zepbound are brand names for the same drug. In the Netherlands and the rest of Europe, it is called Mounjaro for both diabetes and weight management. In the United States, Lilly uses two names: Mounjaro for type 2 diabetes and Zepbound for obesity and sleep apnea. The European registration for type 2 diabetes came in 2022, for weight management at the end of 2023. The drug is supplied in the Netherlands in a pre-filled pen (KwikPen) with multiple doses. If you encounter 'tirzepatide' online as loose powder, vial, or 'peptide', it is not a registered medicine. The quality and dosage are unknown, and the NVIC (Dutch Poisons Information Centre) reports an increase in poisoning notifications from weight loss products bought online. Read more about the pen and its use on our page about Mounjaro.
Is tirzepatide reimbursed? (as of October 2026)
Tirzepatide is currently not reimbursed for weight loss from the basic health insurance package. Reimbursement is only possible for type 2 diabetes, under strict conditions. That may change. The Dutch Healthcare Institute (Zorginstituut) is assessing whether Mounjaro for obesity should be included in the basic package. These are the steps:
- October 5, 2026: first discussion in the Scientific Advisory Board (WAR). This is an internal discussion, not a decision.
- October 12–18, 2026: technical consultation, where parties can respond.
- Not yet scheduled: second WAR discussion, advice from the Advisory Committee Package, and then advice to the minister. The Zorginstituut is considering a tiered approach, where the patient group with the highest health risks would first qualify. For comparison: for semaglutide (Wegovy), the Zorginstituut advised in July 2024 not to reimburse it. So, nothing will change in the short term. We will update this blog after each step; also read Will Mounjaro or Wegovy be reimbursed soon?
The future of tirzepatide
Tirzepatide is also the basis for the next generation of weight loss drugs. At the EASD diabetes conference (September 2026), Lilly presented 'eloraTZP': tirzepatide combined with eloralintide, which mimics the satiety hormone amylin. In a phase 2b study in people with obesity and type 2 diabetes, the highest combination resulted in −23.3% in 48 weeks, compared to −14.8% with tirzepatide alone. However, more participants stopped due to side effects. Phase 3 starts at the end of 2026; the drug is still a long way from being available. In addition, Lilly is investigating retatrutide, which acts on glucagon in addition to GIP and GLP-1. Read more about this on our page about retatrutide. This drug is also not registered in the Netherlands.
