Mounjaro is more effective for weight loss than Ozempic. So how does it work? And why does it cost so much?

A weight-loss drug more effective than Ozempic and Wegovy has recently been approved in Australia.

The drug, tirzepatide, is sold under the brand name Mounjaro and affects feelings of hunger and fullness, as well as changing how the body processess food. (In other countries, tirzepatide is also sound under the brand name Zepbound.)

So how does tirzepatide work and differ from Ozempic? And with a price tage of $315–$645 per month for the starting dose, why is it so expensive?

How does it work?

Think of tirzepatide as a master key that unlocks two important doors in your body’s weight control system. It mimics two hormones: GLP-1 (glucagon-like peptide-1) and GIP (glucose-dependent insulinotropic polypeptide).

When you eat, your body naturally releases GIP and GLP-1 hormones. These hormones play crucial roles in regulating appetite, food intake and blood sugar levels. Tirzepatide mimics and amplifies the effects of these hormones.

By mimicking the GLP-1 and GIP hormones, tirzepatide makes people feel fuller with smaller meals. This can reduce the overall food intake and lead to weight loss over time.

It also helps your body process sugar more effectively and slows down how quickly food leaves your stomach. This results in eating less, feel satisfied for longer and having healthier blood sugar levels.

How does it compare with Wegovy/Ozempic?

Tirzepatide (Mounjaro) and semaglutide (Wegovy/Ozempic) are similar in many ways. Both are injectable medications used for weight loss and work by mimicking hormones that regulate appetite and blood sugar.

The key difference is that tirzepatide acts on two hormone receptors (GIP and GLP-1), while semaglutide only acts on one (GLP-1). This dual action is thought to be why tirzepatide shows slightly better results for weight loss in clinical trials.

Clinical trials have shown participants lost an average of 25% of their body fat in the first year of treatment with tirzepatide. This is when combined with lifestyle counselling from a health-care professional who encouraged a healthy and reduced-calorie diet (500 calories less per day compared to patient’s diet at the beginning of the study) and at least 150 minutes of physical activity per week*.

This compares with an average of 15% weight loss in the first year for semaglutide, also alongside a reduced-calorie diet (a 500 calorie-deficit per day) and increased physical exercise (150 minutes per week).

For a person weighing 120kg, this might mean the difference between losing 30kg with tirzepatide versus 18kg with semaglutide. But of course, with both drugs, some people will lose less weight than the average, some will lose more, and some may not respond to the drug at all.

What are the side effects of tirzepatide?

Like any medication, tirzepatide has side effects. The most common are nausea, vomiting, diarrhoea and constipation. These could feel like a mild tummy bug and are similar to those seen with semaglutide.

For most people, these side effects are manageable and often improve over time.

There are also some rarer, more serious risks to consider. These include inflammation of the pancreas and gallbladder problems. There is also a potential increased risk for thyroid cancer, although this has only been seen in lab rats so far, not humans.

As with Ozempic and Wegovy, when you stop taking tirzepatide, its effects stop. Most people regain some, if not all, of the weight they lost.

Who can access tirzepatide?

In Australia, tirzepatide is approved for use in adults with a body mass index (BMI) of 30 or higher, or a or BMI of 27 or above if you have a weight-related health condition such as diabetes. It can only be prescribed by a doctor, after you have tried other weight-loss methods.

But it’s not suitable for everyone. It shouldn’t be used in pregnancy and may not be suitable for people with certain medical conditions and those with a history of eating disorders.

If you’re considering tirzepatide, it’s important to discuss the benefits and risks for your personal health situation with your doctor.

Why is it so expensive?

Tirzepatide typically costs around A$345 per month for the starting dose. This can escalate to $645 per month for the ongoing “maintenance” dose if a higher dose is necessary for diabetes and/or weight management. This puts the drug out of reach for most people.

Tirzepatide, sold as Mounjaro in Australia, is only available on private prescription and is not subsidised by the Pharmaceutical Benefits Scheme (PBS). This means you pay the full cost of the medication without any government support.

However, the United Kingdom recently announced it would add tirzepatide to the National Health Service in a phased approach over the next three years, so it’s possible we might see it subsidised in Australia in the future.

Developing new drugs is a costly business. Companies spend billions on research, clinical trials, and getting regulatory approvals. They then set high prices to recoup these costs and make a profit.

The patent for tirzepatide lasts until 2036. So we won’t have any cheaper generic versions for more than a decade.

Correction: this article originally said 150 minutes of exercise per day rather than per week.