GLP-1 / incretin
Tirzepatide
Approved (Canada and US)Approved drugMounjaroZepboundTirz
A once-weekly injection from Eli Lilly that acts on GLP-1 and GIP receptors. It's approved for type 2 diabetes (Mounjaro) and weight management (Zepbound), with large trial weight loss and years of real-world use.
- Canada
- Authorized: Mounjaro (type 2 diabetes), Zepbound (weight management; sleep apnea with obesity)
- United States
- Approved: Mounjaro, Zepbound
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Not medical advice — talk to your doctor before making medical decisions.
At a glance
- Class
- GLP-1 / GIP agonist
- Mechanism
- Lowers appetite, slows stomach emptying, improves insulin response
- Evidence
- Approved drug
- Canada
- Authorized (Mounjaro, Zepbound)
- Us
- Approved
- Half Life
- About 5 days
- Routes
- SubQ, weekly (pen)
- Common Side Effects
- Nausea, diarrhea, constipation, vomiting, reflux
- Key Cautions
- Pancreatitis, gallbladder, dehydration; oral birth control less reliable
- Trial Weight Loss
- Up to ~21% at 72 weeks (SURMOUNT-1)
What the research says
Is there a legal, regulated version in Canada?
Yes. Mounjaro and Zepbound are authorized and sold by prescription at pharmacies. A prescribed pen has a DIN and known contents, unlike research vials.
Birth control pills?
Tirzepatide can make oral contraceptives less reliable, especially after starting and after each dose increase. The label suggests a backup or non-oral method for 4 weeks after each of those.
Combine with semaglutide or retatrutide?
No. Overlapping action, more side effects, no evidence of benefit.
How does it compare with semaglutide?
In the head-to-head SURMOUNT-5 trial, tirzepatide gave more weight loss than semaglutide 2.4 mg over 72 weeks (about 20% vs 14%).
Common side effects and cautions
- Nausea, diarrhea, constipation, vomiting and reflux are the most common, mostly in the first weeks and after each dose increase.
- Eating much less can mean losing muscle along with fat. Protein and strength training help protect it.
- Gallstones are more likely with fast weight loss.
- Slowed stomach emptying can change how oral medicines absorb, and matters before surgery or sedation. Tell the anesthetist you're on it.
- If you take insulin or a sulfonylurea, the risk of low blood sugar goes up.
- Not for use in pregnancy or with a personal or family history of medullary thyroid cancer or MEN2 (label warning for this class).
Get medical care if
- Redness, heat, swelling or pus at a site that spreads or comes with fever
- Hives, swelling of the face or throat, or trouble breathing (call 911)
- Severe stomach pain that won't go away, with or without vomiting (possible pancreatitis)
- Pain in the upper right belly, fever or yellow skin or eyes (possible gallbladder problem)
- Can't keep fluids down, very dark urine or dizziness when standing (dehydration, which can affect the kidneys)
- A lump or swelling in the neck, trouble swallowing or a hoarse voice that won't go away
Dose calculator
Doses are set with your prescriber. This converts a dose you already have into what to draw; it doesn't recommend one. Check every number against your syringe and your vial's label.
Doses left in the vial
A blend vial
Not medical advice — talk to your doctor before making medical decisions.
Sources
Researched 2026-10-27. Trial results and approval status change.
General education, not medical advice. Nothing here is a dose recommendation. Doses, schedules and changes are set with a prescriber.