An independent peptide reference — no sellers, every claim sourced

Tirzepatide

Also known as Mounjaro, Zepbound, LY3298176

Dual GIP and GLP-1 receptor agonist, registered for type 2 diabetes and weight management.

clinically proven Metabolic & weight approved drug

At a glance

Category
Metabolic & weight
Status
approved drug
Route
subcutaneous, once weekly
Half-life
approximately 5 days in type 2 diabetes 8 and approximately 5-6 days in patients with overweight or obesity 7, subcutaneous
Onset
weight loss from a few weeks onwards; maximum effect after 9-18 months
Molecular weight
4813.53 Da 7
Sequence
39-amino-acid synthetic peptide based on the GIP sequence, with Aib at positions 2 and 13 and a C20 fatty diacid attached to Lys20 via a γGlu-AEEA-AEEA linker

Registered by the EMA and the FDA. In the US, Mounjaro is indicated as an adjunct to diet and exercise to improve glycaemic control in adults and children aged 10 and over with type 2 diabetes 8, while Zepbound is indicated to reduce excess body weight and maintain weight reduction long term in obesity or overweight with a weight-related comorbidity, and to treat moderate to severe obstructive sleep apnoea in adults with obesity 7. In the EU the Mounjaro brand covers both diabetes and weight management. Prescription only.

Doping status: Not listed by WADA

Checked against the WADA 2026 Prohibited List. For a specific product and country, Global DRO is the lookup athletes are expected to use — the List names substances, not brand names.

Mechanism of action

Tirzepatide activates two incretin receptors simultaneously: the GIP receptor (glucose-dependent insulinotropic polypeptide) and the GLP-1 receptor. The molecular structure is derived from GIP, but it also has affinity for the GLP-1 receptor. Affinity for the GIP receptor is comparable to that of natural GIP; for the GLP-1 receptor the affinity is roughly five times lower than that of natural GLP-1.

Via the GLP-1 receptor the same effects occur as with semaglutide: glucose-dependent insulin secretion, inhibition of glucagon, delayed gastric emptying and central appetite suppression. The added GIP receptor activation appears to contribute to satiety via receptors in the hypothalamus and to lipid metabolism in adipose tissue, where GIP influences the uptake and storage of fatty acids and insulin sensitivity.

Why GIP receptor agonism amplifies the weight effect is still under debate. There are indications that both GIP agonism and GIP antagonism can produce weight loss in animal models; one explanation is that prolonged agonist stimulation leads to receptor desensitisation. The definitive mechanism has not been elucidated.

What the research shows

Strong evidence from large randomised phase 3 trials (SURPASS in diabetes, SURMOUNT in obesity) with thousands of participants. In head-to-head comparison with semaglutide 1 mg (SURPASS-2) and semaglutide 2.4 mg (SURMOUNT-5), tirzepatide produced greater weight loss and a greater fall in HbA1c.

Research in humans

SURMOUNT-1 (n=2539, 72 weeks) showed a mean weight loss in adults with obesity without diabetes of 15.0% (5 mg), 19.5% (10 mg) and 20.9% (15 mg) versus 3.1% with placebo 1. In the SURPASS programme HbA1c fell by approximately 1.9-2.6 percentage points. SURMOUNT-OSA showed a clinically relevant fall in the apnoea-hypopnoea index in obstructive sleep apnoea. SURPASS-CVOT demonstrated non-inferiority to dulaglutide on cardiovascular outcomes.

Animal and lab research

As with other long-acting GLP-1 receptor agonists, dose- and duration-dependent thyroid C-cell tumours were seen in rat studies. The relevance to humans is unknown; this forms the basis for the boxed warning.

Caveats. The clinical programme was designed and funded by Eli Lilly. As with semaglutide, a large part of the weight returns after stopping: in SURMOUNT-4 weight increased again after switching to placebo. A substantial share of the weight lost consists of fat-free mass. Direct comparative data with other agents are limited to a few trials; long-term data beyond around 3 years remain scarce.

What it is used for

  • Type 2 diabetes mellitus in adults and children aged 10 and over, as an adjunct to diet and exercise 8
  • Chronic weight management in obesity (BMI ≥ 30) or overweight (BMI ≥ 27) with a weight-related comorbidity 7
  • Moderate to severe obstructive sleep apnoea in adults with obesity (US indication) 7
  • Investigated in MASH, heart failure with preserved ejection fraction (HFpEF) and chronic kidney disease

Dosing

Dose
2.5 mg to 15 mg per week
Frequency
once weekly, on a fixed day
Route
Subcutaneous into the abdomen, thigh or upper arm; rotate the injection site
Duration
Chronic; maintaining weight loss generally requires continued use
  • Titration schedule: start at 2.5 mg subcutaneously once weekly for 4 weeks. This is a starting dose, not a maintenance dose 78.
  • After 4 weeks increase to 5 mg per week. Further increases in steps of 2.5 mg with an interval of at least 4 weeks at the current dose: 7.5 mg, 10 mg, 12.5 mg and a maximum of 15 mg per week in adults, or 10 mg per week in paediatric patients aged 10 and over 78.
  • For type 2 diabetes, 5, 10 and 15 mg are the maintenance doses; for weight management, 5, 10 and 15 mg are maintenance doses, with 7.5 and 12.5 mg as alternatives in case of tolerability problems.
  • A missed dose can still be given within 4 days (96 hours); after that, skip it and resume the usual schedule 8.
  • When switching to a different injection day there must be at least 3 days (72 hours) between two doses 8.
  • Doses are the official registered schedules. This is reference information, not treatment advice.
  • The schedules above describe the licensed product. Tirzepatide is also widely sold as lyophilised powder in vials outside any approval framework, and is reconstituted and drawn up with an insulin syringe by the buyer. That removes the fixed-dose mechanism of the pen, and none of the registered titration steps have been validated for such material.
  • The milligram-versus-microgram trap is the single most likely way someone is harmed with this drug. Tirzepatide is dosed in milligrams; insulin syringes are marked in units, and one unit is a volume (0.01 ml), not a dose. The same unit count therefore means a different milligram amount at every concentration, and grey-market vials come in at least five different strengths. The FDA's compounding risk alert of 26 July 2024, written about semaglutide but describing the identical failure mode, records patients administering five to twenty times the intended dose after confusing millilitres, milligrams and 'units' — in one reported pattern, patients told to inject 5 units injected 50 4.
  • The FDA states that it has received adverse event reports for compounded semaglutide and tirzepatide products prescribed at doses beyond the approved label, including larger single doses, more frequent dosing and faster titration, and that some of those events were serious. As of 31 May 2026 the agency had received more than 730 adverse event reports associated with compounded tirzepatide, and notes that these are likely to be under-reported because state-licensed pharmacies that are not outsourcing facilities are not required to report 3. Compounding is in any case no longer shortage-justified: the FDA declared the tirzepatide injection shortage resolved on 19 December 2024, enforcement discretion for 503A and 503B compounders ended on 18 February and 19 March 2025, and tirzepatide appears on neither the drug shortage list nor the 503B bulks list 9.
  • Grey-market powder carries no guarantee of identity, purity, sterility or actual milligram content, so the number on the label may not be the number in the vial, and any calculation is only as good as that label. The FDA has warned companies selling tirzepatide, semaglutide and retatrutide labelled 'for research purposes' or 'not for human consumption' directly to consumers with dosing instructions, and has documented fraudulent compounded tirzepatide carrying the name of a licensed pharmacy that did not make it 3.
  • The registered titration schedule exists because gastrointestinal effects are dose-limiting. Starting at 2.5 mg for four weeks and stepping up by 2.5 mg no faster than every four weeks is what makes the drug tolerable; beginning at a maintenance dose such as 10 or 15 mg is how people end up vomiting for days and dehydrated. With a half-life of roughly five days, an overdose is not something that resolves overnight.

These figures describe what the literature and published protocols report. They are not advice and not a dosing instruction.

Protocols

Mounjaro titration (type 2 diabetes)

approved product information

Source: FDA prescribing information for Mounjaro (DailyMed)

Weeks 1-42.5 mg subcutaneously once weekly
After 4 weeks5 mg once weekly
Each further stepincrease by 2.5 mg after at least 4 weeks on the current dose, if additional glycaemic control is needed
Ceiling15 mg once weekly in adults; 10 mg once weekly in paediatric patients

2.5 mg is a starting dose, not a maintenance dose. Every increase requires at least four weeks at the dose below it.

Zepbound titration (obesity, and obstructive sleep apnoea)

approved product information

Source: FDA prescribing information for Zepbound (DailyMed)

Weeks 1-42.5 mg subcutaneously once weekly (initiation only)
After 4 weeks5 mg once weekly
Each further stepincrease by 2.5 mg after at least 4 weeks on the current dose
Maintenance5 mg, 10 mg or 15 mg once weekly for weight reduction; 10 mg or 15 mg once weekly for obstructive sleep apnoea
Ceiling15 mg once weekly for all indications

The same ladder as Mounjaro, but a different set of maintenance doses: 5 mg is not an option for the sleep apnoea indication. If a maintenance dose is not tolerated the label says to consider a lower one rather than to stop.

Grey-market powder, weekly ladder run to maximum

user protocol — not validated

Source: Pattern circulating among users and sellers of unlicensed tirzepatide powder

This is not a validated schedule. It is a pattern that circulates among users and sellers, reproduced because it is what people actually follow — not because it has been tested. No trial established these doses, this interval or this duration, and nobody is checking what is in the vial. Treat every number below as an assertion, not a finding.

Weeks 1-42.5 mg once weekly
Weeks 5-85 mg once weekly
Weeks 9-127.5 mg once weekly
Weeks 13-1610 mg once weekly
Weeks 17-2012.5 mg once weekly
Week 21 onward15 mg once weekly

This is the label's 2.5 mg ladder run straight to its ceiling. The label does not schedule those higher steps — there each one is conditional on needing more effect, and 5 mg or 10 mg is a maintenance dose in its own right. Grey-market vials circulate at several strengths, so an identical syringe reading is a different milligram amount from one vial to the next.

Schedules are reproduced as their source states them. Units, IU and milligrams explains why the figures are not interchangeable between products.

Reconstitution

Vial sizes
10 mg, 15 mg, 20 mg, 30 mg, 60 mg
Solvent
bacteriostatic water (0.9% benzyl alcohol) — for grey-market powder only; the licensed presentation is a ready-made solution and is never reconstituted
Storage
Licensed presentation: 2-8 °C in the refrigerator, do not freeze, in the original packaging to protect from light. If needed, up to 21 days at room temperature up to 30 °C; after that discard and do not refrigerate again. Unregistered powder: no approved storage instruction exists. The FDA has separately received complaints that compounded GLP-1 products arrived warm or with inadequate ice packs, and advises against using any injectable GLP-1 drug that arrives insufficiently refrigerated.

Worked example

Two different products, and the entry does not treat them as one. The licensed product (Mounjaro, Zepbound) is supplied as a ready-to-use solution in a prefilled single-dose pen or single-dose vial at a validated concentration: nothing is dissolved, nothing is measured. Separately, tirzepatide is sold as lyophilised powder in vials outside any approval framework, and that material is reconstituted and measured by the buyer. For such a vial: 30 mg vial + 3 ml bacteriostatic water = 10 mg/ml. A 2.5 mg starting dose is 0.25 ml, which is 25 units on a U100 insulin syringe. A 15 mg dose from the same vial would be 1.5 ml — more than one full syringe, which is itself a warning that the concentration is wrong for that dose. Reconstituting the same 30 mg vial with 1.5 ml instead gives 20 mg/ml, at which 2.5 mg is 12.5 units. The vial has not changed; the meaning of a 'unit' has halved.

Vial strengths are not standardised between sellers. 10, 15, 20, 30 and 60 mg vials all circulate, so two vials that look identical can differ sixfold in content and the concentration must be recalculated for every one. A unit figure copied from another person's protocol is meaningless unless their vial strength and water volume matched yours. Underneath all of it, the arithmetic rests on a label no regulator has checked: identity, purity, sterility and actual milligram content of grey-market powder are unverified. The licensed pen delivers a validated dose; the powder is a separate, unapproved supply route.

Work it out for Tirzepatide

Safety

Side effects

  • Nausea, diarrhoea, vomiting, constipation, abdominal pain — very common, especially during dose increases; the label lists these among the most common adverse reactions 7
  • Reduced appetite, dyspepsia, belching, bloating
  • Injection site reactions, fatigue, hair loss, gastro-oesophageal reflux disease 7
  • Gallstones and cholecystitis with rapid weight loss
  • Acute pancreatitis (rare)
  • Delayed gastric emptying up to gastroparesis; risk of aspiration of gastric contents under anaesthesia
  • Hypoglycaemia in combination with sulfonylureas or insulin
  • Worsening of diabetic retinopathy with rapid glycaemic improvement
  • Loss of fat-free mass
  • Possible reduced efficacy of oral contraceptives in the initial period after starting and after each dose increase 78
  • Overdose from a dosing error with reconstituted powder: severe and protracted nausea, vomiting and abdominal pain, dehydration, fainting and headache, with pancreatitis and gallbladder events also reported in this class. With a half-life of about five days, the effects of a tenfold error persist for days
  • Injection-site infection and abscess from non-sterile technique or non-sterile starting material — a vial-and-syringe risk that does not exist with the sealed licensed pen

Do not use if

  • Personal or family history of medullary thyroid carcinoma (MTC) — a labelled contraindication 78
  • Multiple endocrine neoplasia syndrome type 2 (MEN 2) — a labelled contraindication 78
  • Hypersensitivity to tirzepatide or any of the excipients
  • History of pancreatitis — relative contraindication
  • Severe gastrointestinal disorders including gastroparesis
  • Pregnancy and breastfeeding
  • FDA boxed warning: tirzepatide causes thyroid C-cell tumours in rats, and it is unknown whether it causes them, including medullary thyroid carcinoma, in humans 78
  • Reconstituting and measuring unregulated powder without being able to do the milligram-to-unit conversion reliably. Tenfold errors at this step are the most frequently documented mechanism of harm with drugs in this class, and the FDA has recorded adverse events, some requiring hospitalisation, from them 4
  • Any assumption that a grey-market vial contains what its label states. Identity, purity, sterility and milligram content are unverified, and the FDA has documented fraudulent compounded tirzepatide labelled with the name of a pharmacy that did not compound it 3

Interactions

Tirzepatide delays gastric emptying and may affect the absorption of oral medication. For oral hormonal contraceptives the label advises switching to a non-oral method of contraception, or adding a barrier method, for 4 weeks after initiation and for 4 weeks after each dose escalation 78. In combination with sulfonylureas or insulin, a dose reduction of those agents is often needed because of the risk of hypoglycaemia. Because of delayed gastric emptying, anaesthesiology guidelines advise adjusting fasting policy around procedures.

Common questions

What is tirzepatide?
A dual GIP and GLP-1 receptor agonist, approved for type 2 diabetes (Mounjaro) and weight management (Zepbound). Acting on both incretin receptors is what sets it apart from single-target GLP-1 drugs such as semaglutide.
Is Mounjaro the same as Zepbound?
Yes — the same drug, tirzepatide, branded Mounjaro for diabetes and Zepbound for weight loss.
Is tirzepatide stronger than semaglutide?
In the trials it has generally produced larger average weight loss, consistent with its extra action at the GIP receptor — though response varies between people. See the full comparison.

Sources