Dr Nick Fuller
Leading Obesity Expert at the University of Sydney and founder of Interval Weight Loss.
If you’ve been paying attention to the latest weight loss treatments, you’ve probably heard of Mounjaro (tirzepatide). It’s one of the most talked-about injections in the health world right now, with studies showing it can help people shed significant amounts of weight. In fact, research found that participants lost up to 22.5% of their body weight over 72 weeks. These results go far beyond what lifestyle changes alone usually achieve.
But the big question remains: does Mounjaro really work for weight loss, or is it just hype?
Mounjaro belongs to a class of medications known as GLP-1/GIP receptor agonists. These drugs mimic natural gut hormones that help regulate appetite, digestion and blood sugar. Unlike older treatments, Mounjaro works on two pathways instead of one, which is why it’s proving so powerful in weight management.
Research shows that GLP-1 receptor agonists alone can significantly reduce appetite and slow gastric emptying, leading to reduced food intake and weight loss. Mounjaro, however, takes this a step further by also activating GIP receptors. Early studies suggest that GIP may enhance the effects of GLP-1, improving insulin sensitivity and amplifying weight reduction benefits.
In the SURPASS-2 clinical trial, participants using tirzepatide (the active ingredient in Mounjaro) achieved significantly greater weight loss compared to those using semaglutide, another leading GLP-1 therapy. This dual action is what makes Mounjaro stand out as one of the most promising next-generation weight loss injections available today.
Mounjaro takes a multi-layered approach to help you feel fuller, eat less and burn energy more effectively. This is one reason it’s become such a breakthrough option for people struggling with obesity or related conditions. Here’s a closer look at how it supports weight loss.
One of the hardest parts of losing weight is constant hunger. Mounjaro helps quiet those signals by telling your brain you’re full, even with smaller meals. This makes it much easier to cut calories without feeling deprived all day.
Learn what to eat while taking weight loss injections to support satiety and results here.
When food leaves your stomach more slowly, you stay satisfied for longer. This reduces the urge to snack between meals or pile your plate within seconds. Studies show that delayed gastric emptying can lead to fewer cravings and reduced overall calorie intake.
By helping your body use insulin more effectively, Mounjaro keeps blood sugar levels stable. This reduces fat storage and supports steady energy throughout the day. Better insulin sensitivity is especially beneficial for people living with type 2 diabetes.
Many people struggle with intense cravings for sweets or fried foods, which often sabotage progress. Mounjaro influences brain reward centres, making these foods less tempting. Over time, this shift helps reinforce healthier eating patterns.
Feeling full with less food is a game-changer for weight loss. Mounjaro helps recalibrate your sense of satiety so you naturally eat smaller portions. This gradual change makes it easier to maintain progress long-term.
Understanding how Mounjaro works is one thing, but using it correctly is another. To see real results and minimise side effects, it’s important to follow the right process under medical supervision. Here are the key steps for safe and effective use.
Always start by speaking to a doctor, who will check your eligibility and medical history. They’ll also rule out any conditions that could make Mounjaro unsafe. This ensures your treatment plan is tailored to your needs.
Most people begin with a low dose, such as 2.5 mg, to let the body adjust. This helps reduce common side effects like nausea or upset stomach. Jumping straight to higher doses is not recommended.
Your doctor will gradually increase your dose over several weeks. This stepwise approach allows your body to adapt while still promoting weight loss. Skipping or rushing this phase can lead to unnecessary discomfort.
Consistency is vital with Mounjaro. Pick one day a week that works for you and stick with it, whether it’s Monday morning or Friday night. Setting reminders can help keep you on track.
To avoid skin irritation, rotate where you inject — stomach, thigh, or upper arm. Changing spots helps prevent lumps or tenderness. It also ensures the medication absorbs properly.
Mounjaro isn’t a free pass to eat whatever you like. Pairing it with a diet rich in lean proteins, vegetables and whole grains leads to the best results. Think of the medication as a tool that supports good nutrition, not replaces it.
Adding physical activity makes Mounjaro even more effective. Exercise boosts metabolism, burns calories and improves overall health. Even 30 minutes of walking or strength training most days can give your results a lift.
For more guidance, see Can You Exercise While on Weight Loss Injections?
Keeping a log of your progress helps you and your doctor see what’s working. Write down weight changes, side effects and energy levels. This record can guide adjustments and keep you motivated.
Mounjaro should be stored in the fridge until it’s ready to use. Incorrect storage can make it less effective. Always follow the storage directions provided by your pharmacy.
Ongoing check-ins help monitor your progress and adjust dosages if needed. They also provide a chance to talk through any side effects. Regular support boosts both safety and success.
Of course, no medication is without risks, and Mounjaro is no exception. While most side effects are mild and improve with time, it’s important to be aware of them before starting treatment. The common and less common reactions you might encounter are as follows:
Nausea – A common side effect, especially at the start.
Vomiting – Can occur if your dose is increased too quickly.
Diarrhoea – Some people experience loose stools as their body adjusts.
Constipation – For others, digestion slows down instead.
Abdominal pain – Cramping or discomfort may occur.
Headache – Reported by some during the adjustment phase.
Fatigue – Tiredness is possible while your body adapts.
Dizziness – Less common but still noted in studies.
Bloating – Temporary stomach discomfort may happen.
Risk of pancreatitis (rare) – Serious but uncommon, requiring urgent medical attention.
Some side effects, like fatigue, are common to GLP-1 medications in general. We explore similar experiences in our article Does Semaglutide Make You Tired?.
So, does Mounjaro really work for weight loss? The evidence strongly suggests yes, it’s one of the most effective weight loss injections currently available, delivering both significant weight reduction and improved metabolic health.
That said, it works best when paired with lifestyle changes, and it’s not suitable for everyone. With proper medical guidance, consistency and healthy habits, Mounjaro can be a powerful partner on your weight loss journey.
Dr Nick Fuller is the founder of Interval Weight Loss and is a leading obesity expert at the University of Sydney with a Ph.D. in Obesity Treatment. Dr Fuller is also the author of three best-selling books and his work been published in top ranked journals in the medical field, including JAMA, Lancet and American Journal of Clinical Nutrition.