Same medicine, same strengths
The description sections of the two labels are almost word for word the same; the only change is that the Mounjaro® version calls tirzepatide a once weekly agonist [1][2]. Both describe tirzepatide, a GIP receptor and GLP-1 receptor agonist based on the GIP sequence, with a molecular weight of 4813.53 daltons. Both list the same six strengths, from 2.5 mg to 15 mg, in single-dose pens and vials holding 0.5 mL.
Both also come as multi-dose vials or pens holding four weekly doses of 0.6 mL each. The pharmacology is described the same way: about 99% bound to albumin, steady levels after about 4 weeks of weekly use, and similar exposure whether injected into the abdomen, thigh or upper arm [1][2]. The storage rules in section 16.2 match line for line.
Different approved uses
- Mounjaro®: alongside diet and exercise, to improve blood sugar control in type 2 diabetes for adults and for children from the age of 10; and, in adults with type 2 diabetes who are at high risk, to cut the chance of major cardiovascular events (cardiovascular death, heart attack or stroke) [1].
- Zepbound®: used together with eating fewer calories and moving more, to bring weight down and hold the loss over the long term in adults with obesity, or overweight with at least one weight-related condition; and to treat moderate to severe obstructive sleep apnoea in adults with obesity [2].
- The Zepbound® label advises against using it together with any other tirzepatide product or any GLP-1 receptor agonist. Mounjaro® contains tirzepatide, so the two are not meant to be combined [2].
The trials behind each label
Section 14 of each label rests on different studies. For Mounjaro®, five SURPASS trials in adults with type 2 diabetes compared tirzepatide with placebo, semaglutide 1 mg, insulin degludec or insulin glargine; a 30-week trial enrolled 99 children and teenagers; and SURPASS-CVOT randomised 13,299 adults with type 2 diabetes and established heart disease to tirzepatide or dulaglutide [1].
In SURPASS-CVOT, a first major cardiovascular event occurred in 12.1% on tirzepatide and 13.0% on dulaglutide over a median of 210.1 weeks, a hazard ratio of 0.92. That met the trial’s test for non-inferiority; superiority over dulaglutide was not established [1]. The article on the Mounjaro® heart indication covers that trial in detail.
For Zepbound®, Study 1 enrolled 2,539 adults with obesity or overweight and no diabetes and Study 2 enrolled 938 adults with type 2 diabetes, both for 72 weeks against placebo. Study 3 began with an intensive lifestyle lead-in and Study 4 tested what happened when some people were moved to placebo. Studies 5 and 6 followed 469 adults with obesity and moderate to severe obstructive sleep apnoea for 52 weeks [2].
How the dose steps are described
Both labels start at 2.5 mg once weekly and climb in 2.5 mg increments, holding each dose for 4 weeks or longer before the next step, which they say reduces the risk of stomach side effects. The wording around those steps differs [1][2].
The Mounjaro® label increases the dose if more blood sugar control is needed, up to 15 mg weekly in adults and 10 mg in children. The Zepbound® label says the 2.5 mg dose is only for starting treatment and is not a maintenance dose. It describes maintenance doses of 5, 10 or 15 mg for weight reduction and 10 or 15 mg for sleep apnoea, chosen by response and tolerability [1][2].
Rules that are the same
- Missed dose: a late dose can still be given within 4 days (96 hours) of the missed one. After that, it is skipped and the next dose goes on the usual day [1][2].
- Changing the weekly day: allowed as long as at least 3 days (72 hours) separate two doses [1][2].
- Where to inject: the abdomen or thigh; the back of the upper arm only when someone else injects. Rotate sites with each dose [1][2].
- Storage: refrigerate, do not freeze, and protect from light. Single-dose pens and vials may be kept unrefrigerated up to 30°C for a total of 21 days; multi-dose vials and pens are discarded 30 days after first use or after 4 doses, even if medicine is left [1][2].
Reading the side effect numbers
Each label reports the side effects seen in its own trials, in different people. The Mounjaro® label lists the most common ones, reported in at least 5% of patients, as nausea, diarrhoea, decreased appetite, vomiting, constipation, indigestion and abdominal pain [1].
The Zepbound® list is longer. It includes the digestive effects plus injection site reactions, fatigue, hypersensitivity reactions, burping, hair loss and gastro-oesophageal reflux [2]. Part of the gap comes from who was studied and how each table is built: the Zepbound® trials ran for up to 72 weeks in adults with obesity or overweight, its table starts at 2%, and even its placebo group reported nausea twice as often as the placebo group in the Mounjaro® pool [1][2].
The rows below put the same item from each label side by side. They come from separate trials in different people; they are not a head-to-head comparison, and they do not show that one brand causes more side effects than the other.
The warnings are largely shared, including the boxed warning about thyroid C-cell tumours in rats, pancreatitis, gallbladder disease, kidney injury from dehydration and aspiration during anaesthesia [1][2].
| Item and label section | Mounjaro® (adults with type 2 diabetes) | Zepbound® (adults with obesity or overweight) |
|---|---|---|
| Pool behind the main table (6.1) | Two placebo-controlled trials, 718 people on tirzepatide, mean 36.6 weeks [1] | Studies 1 and 2, 2,519 people on tirzepatide, up to 72 weeks [2] |
| Cut-off for the main table (6.1) | At least 5% and more often than placebo [1] | At least 2% and more often than placebo [2] |
| Nausea: placebo, then 5 / 10 / 15 mg (6.1) | 4%, then 12% / 15% / 18% [1] | 8%, then 25% / 29% / 28% [2] |
| Any digestive reaction: placebo, then 5 / 10 / 15 mg (6.1) | 20.4%, then 37.1% / 39.6% / 43.6% [1] | 30%, then 56% at each dose [2] |
| Stopped because of digestive reactions: placebo, then 5 / 10 / 15 mg (6.1) | 0.4%, then 3.0% / 5.4% / 6.6% [1] | 0.5%, then 1.9% / 3.3% / 4.3% [2] |
| Severe digestive reactions: placebo, then 5 / 10 / 15 mg (5.6 and 5.2) | 0.9%, then 1.3% / 0.4% / 1.2% [1] | 1%, then 1.7% / 2.5% / 3.1% [2] |
| Average change in heart rate (6.1) | Up 2 to 4 beats per minute, against 1 on placebo [1] | Up 1 to 3 beats per minute, against none on placebo [2] |
| People who formed anti-tirzepatide antibodies (12.6) | 51% across seven diabetes trials [1] | 64.5% in Studies 1 and 2; 60.6% in the sleep apnoea studies [2] |
| Elimination half-life (12.3) | About 5 days [1] | About 5 to 6 days [2] |
| Time to the highest blood level after a dose (12.3) | 8 to 72 hours [1] | Median 24 hours, range 8 to 72 [2] |
| Share aged 65 or older in the pooled trials (8.5) | 30.1% of the seven-trial pool [1] | 9% of Studies 1 and 2 [2] |
Warnings written for different readers
- Low blood sugar: the Mounjaro® label ties the risk to use with insulin or a sulfonylurea. The Zepbound® label says the medicine itself lowers blood glucose, reports low readings in 4.2% against 1.3% on placebo in its diabetes trial and in 10.3% of those also on a sulfonylurea, and mentions cases in adults without diabetes [1][2].
- Eyes: both labels say diabetic retinopathy can worsen for a while when glucose control improves quickly; the Zepbound® heading limits the point to people with type 2 diabetes [1][2].
- Blood pressure: only the Zepbound® label reports low blood pressure, in 1.6% against 0.1% on placebo, and more often in people taking blood pressure medicines [2].
- Hair: Zepbound® lists hair loss in its main table and reports it in 7.1% of women against 0.5% of men on tirzepatide; the Mounjaro® label lists alopecia among postmarketing reports [1][2].
- Gallbladder: Mounjaro® reports acute gallbladder disease in 0.6% against none on placebo; Zepbound® splits it into gallstones (1.1% against 1%), inflammation (0.7% against 0.2%) and removal of the gallbladder (0.2% against none) [1][2].
- Insulin users: only the Mounjaro® label explains that insulin and tirzepatide are separate injections, never mixed, which may go in the same body region though not side by side [1].
Pregnancy and children
The pregnancy sections are written for different situations. The Zepbound® label says weight loss offers no benefit during pregnancy and may harm the fetus, and that it should be stopped when a pregnancy is recognised; it also lists a pregnancy exposure registry. The Mounjaro® label, written for diabetes, says it should be used in pregnancy only if the potential benefit justifies the potential risk, and notes the risks of poorly controlled diabetes [1][2].
Both labels say the same about the pill: for four weeks at the start and four weeks after every step up, pill users are pointed to a contraceptive that is not swallowed, or to a condom alongside the pill. On children, Mounjaro® is approved from age 10 for type 2 diabetes, and its label says the multi-dose pen is not recommended for children to inject themselves. The Zepbound® label says safety and effectiveness have not been established in children [1][2].
The breastfeeding sections are identical. In a single-dose study in 11 women, tirzepatide could not be detected in 164 of 171 milk samples, and neither label has data on effects in the breastfed infant or on milk production [1][2].
Outside the US
The two-brand split is a US and Canadian arrangement. In the European Union there is one product, Mounjaro®, authorised for type 2 diabetes from age 10 and for weight management in adults; sleep apnoea and heart failure trial results appear in its section 5.1 rather than as separate indications [3][4].
The EU text is also worded differently in places. Its contraindication section lists only hypersensitivity, the thyroid tumour findings in rats sit in the preclinical section, and it advises stopping tirzepatide at least one month before a planned pregnancy because of its long half-life [3].
Health Canada keeps both names, each with its own monograph: Mounjaro® for type 2 diabetes in adults and in young people aged 10 to under 18, and Zepbound® for chronic weight management and sleep apnoea, supplied only as a four-dose KwikPen® [5][6]. Both Canadian monographs list pregnancy as a contraindication and include a warning on non-arteritic anterior ischemic optic neuropathy (NAION), an eye condition reported with GLP-1 receptor agonist products; the US labels checked for this article carry no such warning [1][2][5][6].
Which brand name you see on the box, and what it is approved for, depends on where you live. The leaflet in your pack is the version that applies to you.
If your prescription changes brand or device
Neither US label has a section on moving from one brand to the other. Both ask that you be trained again whenever the presentation changes, for example from a single-dose pen to a KwikPen® or a vial, and the Zepbound® label advises against pairing it with any other tirzepatide product [1][2]. How a change is made, and at which dose, is your prescriber’s decision.
Because the multi-dose vials and pens hold four doses and have a 30-day limit after first use, it helps to know which dose you are on and when the container was opened.
Mounjaro® and Zepbound® are registered trademarks of Eli Lilly and Company. PepLabo is not affiliated with or endorsed by Eli Lilly and Company.
When to get help
| Sign | Who to contact | How fast | Source |
|---|---|---|---|
| A sudden loss of sight in one eye, even if partial | Urgent eye examination | Emergency | Canadian monographs, NAION warning [5][6] |
| Changes in your vision, especially if you have had diabetic retinopathy | Your prescriber | Today | US labels, sections 5.7, 5.8 and 17 [1][2] |
| Shakiness, sweating, dizziness, hunger or a racing heartbeat while tirzepatide is used with insulin or a sulfonylurea | Your prescriber, the same day | Today | US labels, sections 5.3, 5.7 and 17 [1][2]; MedlinePlus [7] |
| A pregnancy while using Zepbound®, or a planned pregnancy on either brand | Your prescriber | Today | Zepbound® label, sections 8.1 and 17 [2]; EU product information, section 4.6 [3] |
| An operation or procedure with anaesthesia or deep sedation coming up | The surgical team and your prescriber, before the procedure | At your next appointment | US labels, sections 5.9 and 17 [1][2] |
