Ozempic or Mounjaro: the difference and what it means for your blood values

The difference between Ozempic and Mounjaro is the number of hormone routes. Ozempic contains semaglutide and acts on GLP-1. Mounjaro contains tirzepatide and acts on GLP-1 and on GIP.

In the trials tirzepatide produced the largest weight loss: 20.9% over 72 weeks against 14.9% for semaglutide over 68 weeks (Jastreboff et al., 2022; Wilding et al., 2021).

Those are separate trials with different participants, so the figures do not line up one to one. There is one study that compared the two directly.

Which drug you receive is your doctor to decide. What you can do yourself is track what the drug does in your blood.

What is the difference between Ozempic and Mounjaro?

Both are weekly injections that dampen appetite through gut hormones. Ozempic mimics GLP-1 only. Mounjaro mimics GLP-1 and GIP, where GIP plays a part in insulin and in fat storage. In the Netherlands Ozempic is registered for type 2 diabetes, while Wegovy contains the same substance and is registered for weight management.

A review in the BMJ describes this difference in mechanism in more depth (Lang, 2025).

Which drug produced more weight loss?

In SURPASS-2 tirzepatide and semaglutide 1 mg were compared directly in people with type 2 diabetes over 40 weeks. All three tirzepatide doses produced a larger reduction in HbA1c and in weight than semaglutide (Frias et al., 2021). That is the only comparison of the two within a single trial.

Note what was actually compared. Semaglutide sat at 1 mg there, not the 2.4 mg used for weight management.

A stronger drug is also not automatically the fitting drug. That depends on your situation, your earlier experiences and what your doctor considers sensible.

Do the side effects differ?

The complaints closely resemble each other, because both drugs act on the same GLP-1 route. Nausea, constipation and diarrhoea are the most common on both, mainly in the first weeks and after a dose increase. Rarer problems involving the pancreas and gallbladder are described for the group as a whole, not for one of the two in particular.

A meta-analysis of 76 trials found an increased risk of gallbladder and biliary disease with GLP-1 drugs, particularly at higher doses and when used for weight loss (He et al., 2022).

There is one practical difference that gets little attention. Mounjaro produces more weight loss on average, and more weight loss means more change in your stores.

Do the blood values that shift differ?

The safety values are the same for both drugs: lipase, amylase and ALT. The effect values also overlap largely, with HbA1c, fasting glucose and fasting insulin. On tirzepatide, triglycerides often get a little more attention, because the GIP route plays a part in fat metabolism.

So the real difference is not in which values move. It is in how far they move.

Take two men of 105 kilos starting on the same day, one on semaglutide and one on tirzepatide. After a year the first is 15 kilos down and the second 22. In the second, ferritin fell from 90 to 34 micrograms per litre. In the first it stayed around 80.

I think that is where the most useful rule of thumb sits. The harder the drug works, the sooner it pays to look at your stores as well.

The Dutch Farmacotherapeutisch Kompas describes the registered indication and known side effects for each drug.

How do you approach the choice?

Choosing between the two is a medical judgement and belongs with your doctor, who weighs your history, other medication and what is available. What you do control is whether you record a starting point. Without a baseline any later result is a loose number, whichever drug you use.

That is also the honest answer to the question in the title. For your blood values the brand name matters less than whether anyone is looking.

Our GLP-1 baseline panel covers the effect, safety and deficiency values in one draw, assessed by a BIG-registered doctor.

If you want to go deeper into the mechanism, read how a GLP-1 injection works. For Mounjaro specifically there is more in losing weight with Mounjaro, and the complaints themselves sit in Ozempic side effects.

If you have already had the conversation with your doctor and the prescription is ready, have your starting values measured before you begin.

References

• Frias JP et al. Tirzepatide versus Semaglutide Once Weekly in Patients with Type 2 Diabetes. N Engl J Med. 2021. PMID 34170647
• Jastreboff AM et al. Tirzepatide Once Weekly for the Treatment of Obesity. N Engl J Med. 2022. PMID 35658024
• Wilding JPH et al. Once-Weekly Semaglutide in Adults with Overweight or Obesity. N Engl J Med. 2021. PMID 33567185
• Lang K. Ozempic v Mounjaro: what is the difference between semaglutide and tirzepatide? BMJ. 2025. PMID 39900371
• He L et al. Association of Glucagon-Like Peptide-1 Receptor Agonist Use With Risk of Gallbladder and Biliary Diseases. JAMA Intern Med. 2022. PMID 35344001
• Farmacotherapeutisch Kompas, monographs for semaglutide and tirzepatide.
• Thuisarts.nl, guidance on when to contact your GP.

Every blood test result includes a professional assessment from a BIG-registered doctor. For treatment decisions, discuss your results with your GP.