Ozempic and Wegovy both contain semaglutide, acting on GLP-1. Mounjaro contains tirzepatide, acting on both GIP and GLP-1. Licensed purpose, dose range and reported results differ.
The molecules, not the brands
There are two active ingredients across these three names. Semaglutide is sold as Ozempic and as Wegovy. Tirzepatide is sold as Mounjaro.
Brand names cause most of the confusion. Clinically, the meaningful distinction is semaglutide versus tirzepatide, and which product is licensed for which purpose.
Mechanism: single versus dual action
Semaglutide activates the GLP-1 receptor, reducing appetite and slowing gastric emptying.
Tirzepatide activates GLP-1 and GIP receptors. Acting on both incretin pathways appears to enhance the effect, and this is reflected in larger average reductions in trial data.
Comparison at a glance
| Active molecule | Tirzepatide (Mounjaro) · Semaglutide (Ozempic, Wegovy) |
| Mechanism | Dual GIP + GLP-1 · GLP-1 only |
| Licensed for | Diabetes and weight management, varies by product |
| Frequency | Once weekly for all three |
| Dose ladder | Gradual step-up over months for all three |
| Prescription | Required for all three |
Reported weight reduction
Published trials report average total body weight reductions of roughly 15% for high-dose semaglutide over about 68 weeks, and up to roughly 20% for high-dose tirzepatide over about 72 weeks.
These are trial averages with structured lifestyle support. Individual response varies widely, and the highest doses are not tolerated by everyone.
Side effects
The profiles are broadly similar: nausea, reduced appetite, constipation or loose stools, most pronounced after dose increases.
Serious effects are uncommon but are discussed before starting, along with the symptoms that warrant immediate contact.
So which is better?
The honest answer is that it depends on your diagnosis, your medical history, what you tolerate and what is available. A medicine with the largest trial average is not automatically the right one for you.
If you have type 2 diabetes, that shapes the decision. If you have a history of pancreatitis or certain thyroid conditions, some options are ruled out entirely. This is precisely what a consultation is for.
Cost as a genuine factor
These medicines are expensive, and cost scales with dose. A patient who reaches a high dose will pay substantially more per month than one who responds well at a lower dose.
Since treatment may continue long term, the honest question at consultation is not only what works best clinically but what is sustainable for you over years rather than weeks.
Tolerance often decides it
The medicine that produces the best trial average is irrelevant if you cannot tolerate the dose required. Some patients do considerably better on one molecule than another, and that is only discoverable in practice.
This is a normal part of treatment rather than a failure, and switching is a recognised clinical option.
Questions worth asking your doctor
Which molecule do you recommend for me specifically, and why. What dose do you expect I will need. What will this cost per month at that dose. What happens if I do not tolerate it. What is the plan for stopping.
A clinician who cannot answer these clearly is not giving you enough to make an informed decision.
Frequently asked questions
Which gives the most weight loss?
Can I switch between them?
Are they interchangeable?
Which is cheapest?
Do any work without lifestyle change?
Medical disclaimer. This article is general information, not medical advice, and does not replace consultation with a qualified doctor. The medicines discussed are prescription-only and must be prescribed and monitored by a physician. Outcomes vary between individuals. Never start, stop or change a prescribed medicine without medical advice.