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Tirzepatide guide

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PepCaddie provides educational summaries of published and registered research. It does not sell peptides, provide medical advice, or recommend the use of any investigational substance. Discuss health decisions with a qualified healthcare professional.

This tirzepatide guide covers an approved prescription medicine, which makes it the exception in this library. Where most compounds here rest on animal work, tirzepatide has approved labelling, a trial programme running to tens of thousands of participants, and published results for every pivotal trial1214. That also means the authority on how it is prescribed is the label, not a website.

The short answer

  • What it is: a prescription medicine given by weekly injection that activates two receptors, GIP and GLP-11.
  • Approved? Yes, under two brand names for different things: Mounjaro for type 2 diabetes and cardiovascular risk, Zepbound for weight management and obstructive sleep apnoea1214.
  • Human evidence: extensive and published, including head-to-head trials, a cardiovascular outcomes trial, and a trial of what happens after stopping68.
  • Carries a boxed warning about thyroid C-cell tumours seen in rats, and is contraindicated with a personal or family history of medullary thyroid carcinoma or MEN 21.
  • Compounded and research-grade versions are not this product, and FDA has more than 730 adverse event reports associated with compounded tirzepatide3.

What the trials found

In adults with obesity and without diabetes, mean body weight fell 20.9 per cent on the highest dose over 72 weeks, against 3.1 per cent on placebo6. The same doses produce less weight loss in people who also have type 2 diabetes, 14.7 per cent against 3.2 per cent7, which is why the two trials should never be quoted interchangeably.

For blood sugar, HbA1c fell by roughly 2 to 2.3 percentage points across the diabetes programme10. Against semaglutide, tirzepatide produced more weight loss over 72 weeks, 20.2 per cent against 13.7 per cent910, though that trial and the diabetes comparison were both open-label, meaning everyone knew which drug they were taking.

In people with obesity and moderate to severe sleep apnoea, breathing interruptions fell by 25 to 29 events an hour against 5 on placebo, which is the evidence behind that indication122. A separate trial in heart failure with preserved ejection fraction reported fewer heart-failure events, with the caveat that cardiovascular deaths were numerically higher on very small numbers13.

What the cardiovascular trial actually showed

This is the detail most summaries flatten. The cardiovascular outcomes trial enrolled 13,299 people with type 2 diabetes and existing cardiovascular disease and followed them for a median of about four years. Major cardiovascular events occurred in 12.2 per cent on tirzepatide against 13.1 per cent on dulaglutide. Tirzepatide met the bar for being no worse than dulaglutide, and the formal test for being better was not met111.

There was no placebo group, and the comparator is itself a medicine that reduces cardiovascular events. So the trial supports the conclusion that tirzepatide is not worse than an active treatment; it does not measure how much benefit there is compared with no treatment at all.

What happens if you stop

Unusually for this library, there is a trial that answers this directly. Everyone took tirzepatide for 36 weeks and lost about 21 per cent of body weight. Half then switched to placebo. Over the following year, those who continued lost a further 5.5 per cent while those who stopped regained 14 per cent8.

Safety, as the label states it

Both labels carry a boxed warning about thyroid C-cell tumours observed in rats, noting that whether this applies to humans is undetermined, and both contraindicate the medicine in people with a personal or family history of medullary thyroid carcinoma or MEN 211. Labelled warnings include severe gastrointestinal reactions, acute kidney injury following dehydration, gallbladder disease, pancreatitis, and aspiration during anaesthesia2. Low blood sugar becomes more likely when it is combined with insulin or a sulfonylurea2.

Gastrointestinal effects are the most common adverse events, and led between 4 and 7 per cent of participants to stop treatment in the pivotal obesity trial6. One thing worth flagging because older summaries still repeat it: the suicidal behaviour and ideation warning was removed from the Zepbound label in February 20262.

Why compounded tirzepatide is a different question

Everything above describes the approved product. FDA states that compounded drugs are not approved and are not reviewed for safety, effectiveness or quality before they are sold, and reports more than 730 adverse event reports associated with compounded tirzepatide, including cases involving doses beyond what the label describes343. The agency declared the shortage that drove widespread compounding resolved at the end of 2024, and in April 2026 proposed excluding tirzepatide from the list outsourcing facilities may compound with34.

Pharmacokinetics and sports status

The label gives an elimination half-life of about five days, steady state after four weeks of weekly dosing, and 80 per cent bioavailability1. For athletes: tirzepatide is not on the 2026 WADA Prohibited List, but it is on the 2026 Monitoring Program, in and out of competition, which is where WADA places substances it is watching without prohibiting5.

What is less well established

  • How much of the weight lost is muscle. Only a small imaging substudy has looked, with no strength or physical function outcomes[unverified].
  • Benefit against no treatment for cardiovascular outcomes, since the outcomes trial used an active comparator111.
  • Long-term safety in children: the paediatric trial randomised 99 participants for 30 blinded weeks1214.

Where the rest of the detail lives

The interactive library on the homepage carries the fuller reference entry for tirzepatide. For anyone actually prescribed it, the approved labelling linked in the references below is the authority on how it is used, and it is written for that purpose in a way no summary can replace.

Open the full tirzepatide reference in the library

References

These are the sources behind this page, listed so you can read them yourself rather than take our word for it. Animal and laboratory findings do not establish that something works or is safe in people. Doses and protocols shown on a study card are that study's research parameters, not recommendations. PepCaddie does not sell peptides and does not choose a dose for anyone; this is educational material and it does not replace a qualified healthcare professional.

  • SURMOUNT-1, obesity

    2022

    Human randomised trial

    Adults with obesity or overweight, without diabetes5 mg, 10 mg or 15 mg once weekly, as reported in this trial studied72 weeksBody-weight outcome

    The dose above is the amount used in this study. It is research information, not a recommended dose, and PepCaddie does not convert study doses into human doses.

    The pivotal obesity trial. Mean body weight fell 20.9 per cent on the highest dose and 15.0 per cent on the lowest, against 3.1 per cent on placebo, over 72 weeks. Around nine in ten participants on the higher doses lost at least 5 per cent of body weight. Between 4 and 7 per cent stopped because of adverse events, against 2.6 per cent on placebo.

    Limitation: People with diabetes were excluded, and the results are smaller in people who have diabetes. The trial ran 72 weeks, so it says nothing about what happens beyond that.

    Randomised, double-blind, placebo-controlled phase 3 trialView study: SURMOUNT-1, obesity

  • SURMOUNT-2, obesity with type 2 diabetes

    2023

    Human randomised trial

    Adults with obesity and type 2 diabetes10 mg or 15 mg once weekly, as reported in this trial studied72 weeksBody-weight outcome

    The dose above is the amount used in this study. It is research information, not a recommended dose, and PepCaddie does not convert study doses into human doses.

    The same question asked in people who also have type 2 diabetes. Weight fell 14.7 per cent on the higher dose against 3.2 per cent on placebo, noticeably less than in people without diabetes.

    Limitation: The figures are materially smaller than the trial in people without diabetes, so the two should not be pooled or used interchangeably. The cohort was 60 per cent Hispanic or Latino across seven countries.

    Randomised, double-blind, placebo-controlled phase 3 trialView study: SURMOUNT-2, obesity with type 2 diabetes

  • SURMOUNT-4, what happens after stopping

    2024

    Human randomised trial

    Adults with obesity or overweight, without diabetesMaximum tolerated dose, 10 mg or 15 mg once weekly, as reported in this trial studied88 weeks in totalWeight-maintenance outcome

    The dose above is the amount used in this study. It is research information, not a recommended dose, and PepCaddie does not convert study doses into human doses.

    Everyone took tirzepatide for 36 weeks and lost about 21 per cent of body weight. Half then switched to placebo. Over the next year those who continued lost a further 5.5 per cent, while those who stopped regained 14 per cent. This is the trial that answers what happens when treatment ends.

    Limitation: A withdrawal design: the comparison group is people stopping an effective drug, not people who never took it, so the contrast is larger than a conventional placebo comparison.

    Randomised withdrawal trial after an open-label lead-inView study: SURMOUNT-4, what happens after stopping

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