Mounjaro in New Zealand: Complete Guide to Tirzepatide for Weight Loss

What Is Mounjaro?

Mounjaro is the brand name for tirzepatide, a prescription medication manufactured by Eli Lilly. Originally developed for type 2 diabetes, it has since been approved for chronic weight management in adults with obesity or overweight with weight-related health conditions.

What makes Mounjaro unique is its dual mechanism of action. Unlike Wegovy (semaglutide), which targets only the GLP-1 receptor, Mounjaro activates both the GLP-1 and GIP receptors simultaneously. This dual-action approach produces more pronounced effects on appetite, blood sugar regulation, and fat metabolism.

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How Does Mounjaro Work?

Mounjaro mimics two natural gut hormones that your body releases after eating:

• GLP-1 (glucagon-like peptide-1): Slows stomach emptying, reduces appetite, and improves insulin sensitivity
• GIP (glucose-dependent insulinotropic polypeptide): Enhances insulin secretion, promotes fat breakdown, and may have independent effects on appetite and metabolism

By targeting both pathways, Mounjaro creates a synergistic effect that researchers believe explains its superior weight loss results compared to GLP-1-only medications.

The medication is administered once weekly via a pre-filled injection pen, similar to Wegovy. You inject it under the skin of your abdomen, thigh, or upper arm.

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Clinical Effectiveness: What the Research Shows

Mounjaro's weight loss efficacy has been established through extensive clinical trials, most notably the SURMOUNT program.

SURMOUNT-1 Trial Results

The landmark SURMOUNT-1 trial enrolled 2,539 adults without diabetes over 72 weeks. Results demonstrated:

• 22.5% average body weight loss at the maximum 15mg dose (approximately 24kg for an average participant)
• 63% of participants lost more than 20% of their starting body weight
• Even the lowest 5mg dose achieved approximately 16% weight loss

Head-to-Head Comparison with Semaglutide

The SURMOUNT-5 trial directly compared tirzepatide against semaglutide (the active ingredient in Wegovy). At maximum doses over 72 weeks:

• Tirzepatide achieved 20.2% weight loss
• Semaglutide achieved 13.7% weight loss
• Tirzepatide reduced waist circumference by 18.4cm versus 13.0cm for semaglutide

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Mounjaro Dosing Schedule

Mounjaro uses a gradual dose escalation approach to minimise side effects. The standard titration schedule is:

• Weeks 1-4: 2.5mg once weekly (starting dose)
• Weeks 5-8: 5mg once weekly
• Weeks 9-12: 7.5mg once weekly
• Weeks 13-16: 10mg once weekly
• Weeks 17-20: 12.5mg once weekly
• Week 21+: 15mg once weekly (maximum maintenance dose)

Your prescriber may adjust this schedule based on your response and tolerance. Some patients achieve their goals at lower doses and don't need to reach the maximum.

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Side Effects and Safety Profile

Mounjaro's side effects are similar to other GLP-1 medications. The most common include:

• Nausea (approximately 18% of patients)
• Diarrhoea (approximately 17%)
• Decreased appetite (approximately 11%)
• Vomiting (approximately 9%)
• Constipation (approximately 7%)

These gastrointestinal effects are typically dose-dependent, occurring mainly during the titration phase, and usually resolve within 4-8 weeks as your body adjusts.

Serious but Rare Side Effects

More serious adverse events are uncommon but include:

• Pancreatitis (inflammation of the pancreas)
• Gallbladder problems
• Kidney problems
• Severe allergic reactions

Boxed Warning

Like all GLP-1 medications, Mounjaro carries a boxed warning regarding thyroid C-cell tumours observed in rodent studies. While this hasn't been confirmed in humans, Mounjaro should not be used by anyone with a personal or family history of medullary thyroid carcinoma (MTC) or Multiple Endocrine Neoplasia syndrome type 2 (MEN 2).