Compound guide · Tier A
Tirzepatide
Two receptors instead of one, and the largest weight loss of any approved obesity drug. It also carries the clearest signal in the category for disproportionate lean tissue loss.
The short answer
The most effective approved option on weight loss alone. The lean mass question is unsettled and worth watching rather than dismissing.
At a glance
| Class | Dual GIP and GLP-1 receptor agonist |
| Developer | Eli Lilly |
| Sold as | Mounjaro, Zepbound |
| Regulatory status | Approved. Type 2 diabetes and chronic weight management, with obstructive sleep apnoea added subsequently. Marketed as Mounjaro for diabetes and Zepbound for weight management. Same molecule, two brands. |
| Compounding status | Tirzepatide came off the FDA shortage list, closing the shortage-based compounding route. Compounded tirzepatide is not an FDA-approved product. |
| Anti-doping | Not specifically listed, but captured by S0 for any use outside an approved therapeutic context in tested sport. |
| Our evidence tier | Tier A. Approved medicine |
What it is
Tirzepatide activates two incretin receptors rather than one: GIP as well as GLP-1. The combination produces greater weight loss than GLP-1 agonism alone in head to head comparison, though the mechanistic reason the pairing outperforms is still debated. It is a once-weekly injection.
Who it is for, and who actually takes it
Adults with type 2 diabetes, and adults with obesity or with overweight plus a weight-related comorbidity. The sleep apnoea indication covers moderate to severe obstructive sleep apnoea in adults with obesity.
Demand consistently outstrips the approved populations. Trends data over the last twelve months puts tirzepatide search interest above both semaglutide and retatrutide worldwide, and the grey market tracks that demand.
What the research shows
Mean weight change at 72 weeks, SURMOUNT-1
Adults with obesity or overweight without diabetes, randomised to placebo or one of three tirzepatide doses.
View as table
| Group | % mean weight loss |
|---|---|
| Placebo | 3.1% |
| 5 mg | 15.0% |
| 10 mg | 19.5% |
| 15 mg | 20.9% |
Source: SURMOUNT-1, published 2022.
Dosing
| Stage | Dose |
|---|---|
| Weeks 1 to 4 | 2.5 mg once weekly, for initiation only and not a maintenance dose |
| Week 5 onward | 5 mg once weekly |
| Thereafter | Increases of 2.5 mg after at least 4 weeks at the current dose |
| Maintenance | 5 mg, 10 mg or 15 mg once weekly |
| Maximum | 15 mg once weekly |
This is the escalation set out in the Zepbound prescribing information for chronic weight management, reproduced as published. The stepwise increase exists to reduce gastrointestinal adverse reactions. Doses for type 2 diabetes differ. This records what the label says. It is not a recommendation, and it applies to the approved product under prescription.
What happens when you come off it
SURMOUNT-4 tested this directly. After a 36-week run-in producing 20.9% mean weight loss, participants randomised to placebo regained about 14% of baseline body weight over the following year, while those continuing lost a further 5.5%. Follow-up work indicates much of the regained weight is fat rather than the lean tissue lost during treatment, which means the body composition on the way back up is not the same as on the way down.
What it is being studied for
| Area | Stage of evidence |
|---|---|
| Type 2 diabetes | Approved |
| Chronic weight management | Approved |
| Obstructive sleep apnoea in obesity | Approved |
| Heart failure with preserved ejection fraction and further cardiometabolic indications | Trials registered and reporting |
Common myths
It is just a stronger version of semaglutide.
It is a different molecule with a different mechanism. Tirzepatide activates the GIP receptor in addition to GLP-1. Greater average weight loss is an outcome of that difference, not evidence that it is the same drug at a higher dose.
Mounjaro and Zepbound are different drugs.
Same molecule, different brand names for different approved indications. Mounjaro is licensed for type 2 diabetes, Zepbound for weight management and sleep apnoea.
More weight loss makes it the better choice for everyone.
Routine care body composition work has reported greater relative lean body mass loss with tirzepatide than semaglutide, around a 2.0% excess at twelve months. That finding is from a preprint that has not completed peer review, so we hold it at Tier C, but total weight lost is not the only variable that matters.
Compounded tirzepatide is equivalent because it is the same molecule.
Regulators have logged hundreds of adverse event reports associated with compounded tirzepatide, many involving dosing errors from drawing doses out of multidose vials rather than using a metered pen.
Verifying a purchase
Because tirzepatide is dosed in 2.5 mg steps and the trials distinguish between 5, 10 and 15 mg, net peptide content is the figure that matters most and the one most often missing. A vial labelled by gross mass with no content figure cannot support any accurate calculation. Confirm identity by mass spectrometry: tirzepatide and semaglutide are routinely substituted for one another in counterfeit product.
The general method is set out in our guide to reading a certificate of analysis, which covers the eleven checks that apply to any compound. The points above are the ones specific to Tirzepatide.
Caveats and safety
Gastrointestinal adverse effects are common and dose dependent, which is why the label escalates slowly. Labels carry a boxed warning regarding thyroid C-cell tumours in rodents, with contraindications in personal or family history of medullary thyroid carcinoma or MEN 2. Gallbladder disease and pancreatitis appear in the safety record. The lean mass signal above is unresolved.
Where to get it
We have no vendor link for Tirzepatide. Our affiliate partner does not stock it, and we do not link to sellers we have not looked at.
Sources
- Zepbound prescribing information, FDA
- Zepbound dosage information, Eli Lilly
- Weight regain after GLP-1 interruption, narrative review of randomised studies
- Lean body mass comparison, medRxiv preprint, not peer reviewed
Related compounds
Disclosure. PeptoPurity is an affiliate of CertaPeptides and earns a commission on qualifying purchases made through the vendor link on this page, at no additional cost to you. That relationship does not set the evidence tier, alter the verdict, or change a word of the assessment. Our Tier C and Tier D pages carry the same links as our Tier A pages, with the same conclusions we would publish if we earned nothing. Where the registered, prescribed route is the better option, we say so on the page that would otherwise pay us.
Scope. This is an evidence review, not medical advice. Where an approved label schedule is reproduced it is a record of what a regulator has published about a licensed medicine, not a recommendation and not a schedule for anyone to follow unsupervised. For unapproved compounds we report only the doses used in published studies, attributed to those studies, and we publish no protocols and no reconstitution guidance for any compound. Regulatory status differs between countries and changes over time. Material sold for laboratory research is not approved for human use. Decisions about treatment belong with a qualified prescriber.