Library / Weight and metabolic

Tirzepatide

Also known as Mounjaro, Zepbound

Approved medicine

Dual GIP and GLP-1 receptor agonist peptide given by weekly injection. Approved for type 2 diabetes and for chronic weight management.

Prescription medicine. Only a prescriber can decide whether a medicine suits you and at what dose. This page is information, not a recommendation.

Background

Synthetic 39 amino acid peptide developed by Eli Lilly, built on the sequence of the gut hormone GIP with added GLP-1 activity and a fatty acid chain for once weekly dosing. FDA approved it as Mounjaro for type 2 diabetes in 2022 and as Zepbound for weight management in 2023.

How it is thought to work

Activates both GIP and GLP-1 receptors. This increases insulin release when glucose is high, lowers glucagon, slows stomach emptying and reduces appetite.

What is claimed, and the evidence

Claim	Evidence	Notes
Improves blood sugar control in type 2 diabetes (adults and children 10 and over)	Approved use	Mounjaro label.
Chronic weight management in adults with obesity, or overweight with a weight related condition	Approved use	Zepbound label. SURMOUNT-1: mean weight change of minus 15% to minus 21% at 72 weeks versus minus 3% on placebo.
Treats moderate to severe obstructive sleep apnoea in adults with obesity	Approved use	Zepbound label.
Reduces major cardiovascular events in type 2 diabetes at high cardiovascular risk	Approved use	Current Mounjaro label.
'Research' or compounded tirzepatide is equivalent to the approved medicine	No published evidence	FDA warns such products are of unknown quality; compounding of GLP-1 medicines is banned in Australia since 1 October 2024.

Side effects

Effect	How often	Notes
Nausea	Common	Most common on the label; mainly during dose increases.
Diarrhoea, vomiting, constipation, indigestion and abdominal pain	Common	Label lists these at 5% or more.
Decreased appetite	Common	Label.
Gallbladder disease Serious	Uncommon	Label warning.
Acute pancreatitis Serious	Rare	Label warning.
Low blood sugar with insulin or sulfonylureas Serious	Common	Label warning.
Acute kidney injury from dehydration Serious	Rare	Label warning.
Serious allergic reactions including anaphylaxis and angioedema Serious	Rare	Label warning.
Worsening diabetic eye disease Serious	Uncommon	Label warning in people with existing retinopathy.
Aspiration during anaesthesia or sedation Serious	Rare	Label warning.

Warnings

Boxed warning: causes thyroid C-cell tumours in rats; human relevance unknown. Not for people with a personal or family history of medullary thyroid cancer or MEN 2.
Can cause pancreatitis, gallbladder disease and kidney injury from dehydration; not recommended with severe gastroparesis.
Tell the treating team before surgery or sedation because of aspiration risk.
FDA has warned about dosing errors with compounded tirzepatide and illegal online 'research' products; pharmacy compounded GLP-1 products are not permitted in Australia.

Phase 3 trials

SURMOUNT-5

Phase 3b, Completed, published. 751 participants, 72 weeks, open label. NCT05822830

Population: Adults with obesity without type 2 diabetes.
Arms: Tirzepatide up to 10 or 15 mg weekly, starting at 2.5 mg and stepping up every 4 weeks; Semaglutide up to 1.7 or 2.4 mg weekly
Primary outcome: Percentage change in body weight at week 72.
Results: Body weight changed by minus 20.2% on tirzepatide against minus 13.7% on semaglutide.
Safety: Gastrointestinal effects were the most common, mostly during dose escalation. Treatment discontinuation for adverse events is not given in the abstract.
Source: Aronne LJ et al. N Engl J Med 2025;393:26-36.

Doses in these trials were given under medical supervision.

Regulatory status

Australia: Approved (ARTG, Mounjaro). Schedule 4. Pharmacy compounding of GLP-1 receptor agonists has been prohibited since 1 October 2024.
United States: FDA approved (Mounjaro 2022 for type 2 diabetes; Zepbound 2023 for chronic weight management and obstructive sleep apnoea with obesity). Removed from the FDA drug shortage list in December 2024.

Sources

Also in Weight and metabolic

From the VialOwl library, reviewed 26 September 2026. For education and general information. It is not medical advice and not a recommendation to use Tirzepatide.