If you're exploring weight loss medications like Wegovy, Ozempic, or Mounjaro, you'll quickly come across two names: semaglutide and tirzepatide. These are the active ingredients in these medications — and while both help with weight loss and blood sugar control, they are not the same. This article explains the difference in plain language: how each one works, what the research shows about weight loss, and how to think about which might be right for you.
What is semaglutide?
Semaglutide is the active ingredient in Ozempic and Wegovy. It belongs to a class of drugs called GLP-1 receptor agonists. GLP-1 (glucagon-like peptide-1) is a hormone your body naturally produces after eating. It signals to the brain that you're full, slows the emptying of your stomach, and stimulates insulin production to keep blood sugar stable.
Semaglutide mimics this hormone — but stays active far longer than the natural version. It's administered as a weekly injection.
- Ozempic (semaglutide): approved for type 2 diabetes, up to 2 mg/week
- Wegovy (semaglutide): approved for obesity and overweight treatment, up to 2.4 mg/week
What is tirzepatide?
Tirzepatide is the active ingredient in Mounjaro. It's a dual GLP-1 and GIP receptor agonist. GIP (glucose-dependent insulinotropic polypeptide) is another gut hormone released after meals. It works together with GLP-1: it supports insulin release, reduces appetite, and may improve the body's ability to burn fat.
By activating both receptors simultaneously, tirzepatide works through two hormonal pathways rather than one — and research suggests this dual mechanism produces a stronger overall effect on weight loss.
- Mounjaro (tirzepatide): in the EU approved for both type 2 diabetes and obesity, up to 15 mg/week
Weight loss: what does the research say?
The most direct head-to-head comparison is the SURMOUNT-5 trial, published in The New England Journal of Medicine in 2025. In this study, 751 adults with obesity (without diabetes) were randomly assigned to either tirzepatide (10 mg or 15 mg) or semaglutide (2.4 mg) for 72 weeks.
The results were clear:
| Treatment | Average weight loss |
|---|---|
| Tirzepatide (Mounjaro) | approx. 20.2% of body weight |
| Semaglutide (Wegovy) | approx. 13.7% of body weight |
That means a person weighing 220 lbs (100 kg) would lose about 44 lbs (20 kg) with tirzepatide versus about 30 lbs (14 kg) with semaglutide — over the same period. A 2025 meta-analysis that pooled data from multiple clinical trials and real-world studies confirmed this pattern: tirzepatide produced statistically significantly greater weight loss than semaglutide.
Side effects: are they different?
Both medications cause similar side effects, because they both slow gastric emptying and affect appetite. The most common are:
- Nausea and vomiting — most common during the early weeks
- Diarrhoea or constipation
- Stomach cramps and bloating
- Fatigue
The side effect profiles are broadly comparable. Tirzepatide may cause slightly more frequent gastrointestinal side effects in some patients, likely because of its stronger overall effect. However, this isn't a universal picture — many people tolerate both medications well, and side effects typically ease significantly after the first few weeks as the body adjusts.
Slow dose escalation is key. See our article on dose titration for why starting low and going slow matters.
Dosing and injection pens
Both medications are given as weekly subcutaneous injections (under the skin) using an auto-injector pen. The dose is gradually increased over approximately 20 weeks to minimise side effects.
| Semaglutide (Wegovy) | Tirzepatide (Mounjaro) | |
|---|---|---|
| Starting dose | 0.25 mg/week | 2.5 mg/week |
| Maximum maintenance dose | 2.4 mg/week | 15 mg/week |
| Titration period | approx. 20 weeks | approx. 20 weeks |
Both pens use a click-based dosing system where each click delivers a precise amount of medication. Counting clicks accurately is important for getting the right dose — and that's exactly what ClickDose helps with.
Which medication might be right for you?
There's no one-size-fits-all answer. The choice depends on your medical history, any other conditions you have, how well you tolerate each medication, cost, and your doctor's assessment. Here are some broad considerations:
Semaglutide (Wegovy/Ozempic) may be a good fit if:
- You want the most established GLP-1 treatment with years of long-term data
- You have cardiovascular disease — semaglutide has approval for reducing cardiovascular risk
- You're aiming for 10–15% weight loss and responding well to treatment
Tirzepatide (Mounjaro) may be a good fit if:
- You have severe obesity and need a more significant degree of weight loss
- You've tried semaglutide and haven't had sufficient results
- You want the medication with the strongest documented weight loss effect
Always talk with your doctor before switching or starting any treatment. They know your full health picture and can give you personalised advice.
Summary
Semaglutide and tirzepatide are both effective medications for weight loss, but they differ in mechanism and strength of effect. Tirzepatide works through two hormonal pathways and typically produces greater weight loss than semaglutide. Semaglutide, in turn, has a long and robust track record and specific approvals — such as cardiovascular protection. The best choice depends on your individual circumstances and should always be made together with your doctor.