Ozempic, Wegovy and Mounjaro: how are they different?

How do the three active ingredients differ?

The active ingredient is the first difference. Ozempic and Wegovy contain semaglutide, which mimics a gut hormone called GLP-1 and acts on its receptor [1] [2]. Mounjaro contains tirzepatide, which acts on two receptors: the one for GLP-1 and the one for GIP, another gut hormone [3]. All three belong to the GLP-1 medicines family.

All three are injected once a week [1] [2] [3]. The fact that Mounjaro acts on two receptors does not, by itself, tell you which medicine will suit you better. That becomes clear through follow-up.

What is each one authorised for in Spain?

The authorised indication is not the same for all three. Ozempic is approved for type 2 diabetes [1]. Wegovy is approved for weight management, alongside diet and physical activity [2]. Mounjaro has both indications: type 2 diabetes and weight management [3].

For adults, weight management is authorised for a body mass index of 30 or above, or from 27 if there is a weight-related condition such as high blood pressure [2] [3]. An approved indication does not automatically mean a medicine is right for you. That is for the person treating you to decide, with your medical history in view.

The minimum age also differs. Ozempic is authorised for adults only [1]. Wegovy is authorised from age 12 for weight management, for those weighing more than 60 kg [2]. Mounjaro is authorised from age 10 for type 2 diabetes, but only for adults for weight management [3].

Ozempic, Wegovy and Mounjaro compared

This table brings together the information above, along with public funding in Spain. It does not say which medicine is best; each column answers a different question.

Prior authorisation for Ozempic requires type 2 diabetes, a body mass index of 30 or above, and use alongside other diabetes medicines rather than as monotherapy [4]. Some presentations are not covered [4]. With prior authorisation, Ozempic has a reduced patient contribution: what you pay depends on your circumstances, and some people are exempt [5] [6]. Without funding, Wegovy and Mounjaro are paid for at the full price.

Which leads to greater weight loss in trials?

One trial has compared them head to head. SURMOUNT-5 included adults with obesity and without diabetes. At 72 weeks, mean weight loss was 20.2% with tirzepatide and 13.7% with semaglutide, according to the regimen each person tolerated [7].

These are group averages. In each treatment arm, some people lost considerably more and others considerably less, and the trial did not include people with diabetes [7]. Alongside your medical history, how well you tolerate treatment and whether it is funded, the average figure is only one part of the decision.

The type of weight lost also matters. In a sub-study of another tirzepatide trial, SURMOUNT-1, around three-quarters of the weight lost was fat and one-quarter was lean mass [8]. That is why protein and strength training matter with all three medicines. Opinions from people already taking one describe their experience; they do not replace trial evidence or your doctor’s judgement.

Do the side effects differ between the three?

Digestive side effects are the ones most often discussed in appointments for all three medicines. In Wegovy trials, 72.9% experienced at least one, compared with 47.1% with placebo [9]. With Mounjaro for weight management, 59.2% of one treatment group experienced digestive side effects, compared with 30.3% with placebo [3]. These figures come from different trials and should not be compared with each other.

Nausea, diarrhoea and vomiting occur mainly when the dose is increased and usually last a few days; constipation tends to last longer [2] [3] [9]. In the trials, 4.3% of people taking Wegovy and between 1.9% and 4.4% of those taking Mounjaro stopped because of these side effects, depending on the dose [2] [3].

If a side effect does not go away or stops you eating normally, speak to the person who prescribes your medicine before deciding what to do on your own.

“I’ve heard Mounjaro leads to more weight loss. Should I switch?”

This is the question most often brought to appointments by people who have been taking Ozempic or Wegovy for a while. Your doctor decides whether you should switch medicines, taking into account your medical history, how well you tolerate treatment and what you can afford. We neither recommend nor advise against it here.

What you can do with any of the three is look after your diet and keep active. Obesity management guidelines recommend combining medicines with a suitable diet and physical activity, whichever medicine is used [10]. In appointments, we also include strength training to help preserve muscle.

Your doctor chooses the medicine; we work with you on what you eat and how you move.

What do we see in appointments with these three medicines?

The question we hear most often is why Spain’s public health system funds one but not the others. Funding decisions are made by Spain’s Ministry of Health, which also weighs the impact on public spending. That is why funding for Mounjaro was refused even for type 2 diabetes, the indication for which Ozempic is funded [4].

We also often see these two misunderstandings.

• Thinking Ozempic and Wegovy are different medicines, when they contain the same active ingredient but have different dosing schedules and indications.
• Treating the average result from a trial as the result you will get.