Tirzepatide Reconstitution Calculator
Tirzepatide is a dual GIP and GLP-1 receptor agonist, sold under the brand names Mounjaro and Zepbound and developed as LY3298176. A C20 fatty diacid chain lets it bind albumin, which is what stretches its half-life to roughly 120 hours and makes once-weekly subcutaneous injection possible. It enhances first- and second-phase insulin secretion and lowers glucagon, both glucose-dependently, and it delays gastric emptying — the mechanism behind most of its gastrointestinal effects and its oral-drug interaction profile. Unlike research peptides, it is FDA-approved, prescription-only, and shipped as a ready-to-use solution that requires no reconstitution. The calculator above is for the compounded and grey-market vials sold as a lyophilised powder, which are not the approved product and carry none of its labelling.
What the evidence says
The published trials that established Tirzepatide dosing are reported below, each with the paper it comes from. The structured range table — every range with its experience level, frequency and linked citation — lives in the Dosavy compound library.
Tirzepatide at a glance
- Category
- GLP-1
- Half-life
- 5 d
- Routes
- Subcutaneous
- Regulatory status
- Approved
- Also sold as
- Mounjaro, Zepbound, LY3298176, GIP/GLP-1 dual agonist, twincretin
Mechanism
A dual GIP receptor and GLP-1 receptor agonist. It contains a C20 fatty diacid that enables albumin binding and prolongs the half-life. Tirzepatide selectively binds to and activates both the GIP and GLP-1 receptors — the targets for native GIP and GLP-1 — enhancing first- and second-phase insulin secretion and reducing glucagon levels, both in a glucose-dependent manner. It also delays gastric emptying, which is the basis of most of its gastrointestinal adverse reactions and of its oral-drug interaction profile.
Reconstitution
The FDA-approved product is a ready-to-use clear, colourless to slightly yellow solution supplied in prefilled pens, single-dose vials, multi-dose vials and a KwikPen. It is not a lyophilised powder — no reconstitution is required or appropriate. Lyophilised 'tirzepatide' powder sold outside the approved supply chain is not the labelled product; its identity, purity and concentration are unverified, so label dosing cannot be assumed to transfer to a reconstituted vial of unknown content.
Storage
Refrigerate at 2°C to 8°C; do not freeze and do not use if frozen. Protect from heat and light and keep in the original carton. Single-dose pens and single-dose vials may be kept unrefrigerated at up to 30°C for a total of 21 days, then discarded. Unopened multi-dose vials or single-patient-use KwikPens kept at room temperature must be discarded after 30 days.
Frequency in practice
Once weekly by subcutaneous injection, at any time of day, with or without meals.
Regulatory
FDA-approved and prescription-only. MOUNJARO is approved for type 2 diabetes (adults and, at a lower maximum, patients 10 years and older); ZEPBOUND is approved for chronic weight management and for obstructive sleep apnea in adults with obesity. These are separate products and separate indications sharing one active ingredient.
What to know before anything else
BOXED WARNING: In both male and female rats, tirzepatide causes dose-dependent and treatment-duration-dependent thyroid C-cell tumors at clinically relevant exposures. Whether it causes thyroid C-cell tumors, including medullary thyroid carcinoma (MTC), in humans is unknown — the human relevance of the rodent finding has not been determined.
Contraindicated with a personal or family history of medullary thyroid carcinoma (MTC) or with Multiple Endocrine Neoplasia syndrome type 2 (MEN 2).
Contraindicated after a known serious hypersensitivity reaction to tirzepatide or any excipient; anaphylaxis and angioedema have been reported.
Acute pancreatitis and acute gallbladder disease have been reported; discontinue if pancreatitis is suspected.
Severe gastrointestinal adverse reactions occur; not recommended in patients with severe gastroparesis. Acute kidney injury secondary to volume depletion from vomiting/diarrhoea has been reported.
Combining tirzepatide with insulin or an insulin secretagogue (e.g. a sulfonylurea) raises the risk of hypoglycaemia, including severe hypoglycaemia; the label directs considering a dose reduction of the insulin or secretagogue.
Delayed gastric emptying can impair absorption of oral medications with a narrow therapeutic index (e.g. warfarin). Oral hormonal contraceptives may be less effective — the label directs switching to a non-oral method or adding a barrier method for 4 weeks after initiation and after each dose escalation.
Pulmonary aspiration during general anesthesia or deep sedation has been reported with GLP-1 receptor agonists; tell any anesthetist about current use before an elective procedure.
The titration schedule exists to limit gastrointestinal adverse reactions. Escalating faster than the label directs increases them, and the 2.5 mg dose is explicitly an initiation dose that is not intended for glycaemic control and is not approved as a maintenance dosage.
Tirzepatide questions
Does tirzepatide need to be reconstituted?
No. The product described in the FDA prescribing information is a ready-to-use clear, colourless to slightly yellow solution in prefilled pens, single-dose vials, multi-dose vials and a KwikPen, not a lyophilised powder, so reconstitution is neither required nor appropriate. Powder sold as 'tirzepatide' outside the approved supply chain is not the labelled product: its identity, purity and concentration are unverified, so label dosing cannot be assumed to transfer.
What dosing schedule does the FDA label publish?
The MOUNJARO prescribing information, section 2.1, gives a starting dosage of 2.5 mg subcutaneously once weekly, increased to 5 mg once weekly after 4 weeks, then in 2.5 mg increments after at least 4 weeks on the current dose, to a maximum of 15 mg once weekly in adults. The ZEPBOUND label uses the same 2.5 mg four-week start and lists 5, 10 and 15 mg once weekly as maintenance dosages for weight reduction, and 10 or 15 mg for obstructive sleep apnea. Those are published label figures, not a recommendation for any individual.
Why is the 2.5 mg starting dose not a maintenance dose?
Both labels say so explicitly. MOUNJARO states the 2.5 mg dosage is for treatment initiation and is not intended for glycemic control; ZEPBOUND states it is not approved as a maintenance dosage. The titration schedule exists to limit gastrointestinal adverse reactions, so the four-week holds are part of the tolerability design rather than an arbitrary ramp. Escalating faster than the label directs increases those reactions. Reaching 15 mg from the 2.5 mg start takes a minimum of 20 weeks under the label's 'at least 4 weeks on the current dose' rule.
What is in tirzepatide's boxed warning?
In both male and female rats, tirzepatide causes dose-dependent and treatment-duration-dependent thyroid C-cell tumors at clinically relevant exposures. Whether it causes thyroid C-cell tumors, including medullary thyroid carcinoma, in humans is unknown — the human relevance of the rodent finding has not been determined. It is contraindicated in anyone with a personal or family history of medullary thyroid carcinoma or with Multiple Endocrine Neoplasia syndrome type 2, and after any known serious hypersensitivity reaction to tirzepatide or its excipients; anaphylaxis and angioedema have been reported. Separately, acute pancreatitis and acute gallbladder disease have been reported, severe gastrointestinal reactions can cause volume depletion leading to acute kidney injury, and the drug is not recommended in severe gastroparesis.
How does delayed gastric emptying affect other medications?
It can impair absorption of oral drugs with a narrow therapeutic index, warfarin being the label's example. Oral hormonal contraceptives may be less effective, and the label directs switching to a non-oral method or adding a barrier method for four weeks after initiation and after each dose escalation. Combining tirzepatide with insulin or an insulin secretagogue such as a sulfonylurea raises the risk of hypoglycaemia, including severe hypoglycaemia; the label directs considering a dose reduction of the insulin or secretagogue. The same delayed emptying is why pulmonary aspiration during general anesthesia or deep sedation has been reported with GLP-1 receptor agonists — an anesthetist should be told about current use before an elective procedure.
How is tirzepatide stored?
The FDA prescribing information directs refrigeration at 2°C to 8°C in the original carton, protected from heat and light, and says not to freeze or use product that has been frozen. Single-dose pens and single-dose vials may be kept unrefrigerated at up to 30°C for a total of 21 days, then discarded. Unopened multi-dose vials or single-patient-use KwikPens kept at room temperature must be discarded after 30 days.
Are Mounjaro and Zepbound the same drug?
They share one active ingredient and are separate products with separate approvals. MOUNJARO is approved for type 2 diabetes in adults and, at a lower 10 mg maximum, in patients aged 10 years and older. ZEPBOUND is approved for chronic weight management and for obstructive sleep apnea in adults with obesity. Both are prescription-only. Because they are distinct approvals, the indication, the maximum dosage and the maintenance steps that apply depend on which product was prescribed.
The rest of the math
- Reconstitution calculatorThe full version of the tool above, with syringe barrel sizes and IU conversion.
- Vial longevityHow many doses a vial holds and the date it runs out.
- Cost per doseVial price against doses drawn, so two vial sizes can be compared honestly.
- Half-life and decayFirst-order clearance, time to steady state, and what remains at a given hour.
- GLP-1 titration scheduleEscalation steps and week-by-week timing for GLP-1 receptor agonists.
Same class as Tirzepatide
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