Semaglutide vs Tirzepatide vs Retatrutide Dosing

Last updated: July 2026

Semaglutide, tirzepatide, and retatrutide are three injectable incretin drugs that each climb their own dose ladder: semaglutide runs 0.25–2.4 mg weekly, tirzepatide runs 2.5–15 mg weekly, and retatrutide has been studied from 1 mg up to 12 mg weekly. They are not interchangeable milligram-for-milligram — each activates a different set of hormone receptors, and the number of syringe units you draw depends on your vial concentration, not on which drug it is.

One honesty note before the numbers: semaglutide and tirzepatide are FDA-approved and carry official labels, but retatrutide is investigational. As of writing it is in clinical trials and has no approved label, so every retatrutide figure below comes from published trial protocols, not a marketed dosing schedule. Treat it as research context, not a prescription.

Have a vial and a target dose? Convert any weekly retatrutide dose to exact mL and U-100 syringe units in seconds.

Open the retatrutide calculator →

TL;DR — key takeaways

Three different scales. A 2.4 mg semaglutide dose, a 15 mg tirzepatide dose, and a 12 mg retatrutide dose are each the top of a different number line. Bigger numbers do not mean a stronger drug.
More receptors, roughly. Semaglutide hits one receptor (GLP-1), tirzepatide two (GIP + GLP-1), and retatrutide three (GIP + GLP-1 + glucagon).
Same titration rhythm. All three step the dose up slowly — typically every 4 weeks in the trials and labels — to let gastrointestinal side effects settle.
Units follow concentration. Whether you draw 20, 40, or 60 units depends on the mg/mL strength of your vial, which is exactly what a reconstitution or units calculator solves.
Approval status differs. Only semaglutide and tirzepatide are approved. Retatrutide is not, so its numbers are trial data, not a label.

Why the three dose scales look so different

Semaglutide is a glucagon-like peptide-1 (GLP-1) receptor agonist — it mimics one gut hormone to blunt appetite and slow gastric emptying. Tirzepatide is a dual agonist, adding the glucose-dependent insulinotropic polypeptide (GIP) receptor. Retatrutide goes one further as a triple agonist, adding the glucagon receptor on top of GIP and GLP-1, which is why it is sometimes called a “GGG” agonist. Because each molecule binds a different receptor set with different potency, their effective milligram ranges do not line up. You cannot assume 1 mg of one equals 1 mg of another.

That is also why the raw dose numbers are misleading out of context. Retatrutide was studied up to 12 mg and tirzepatide is approved up to 15 mg, but that does not make either “five times stronger” than semaglutide at 2.4 mg. Each figure is the ceiling of its own separately calibrated ladder.

The slow build matters for tolerability. The appetite and gut effects that drive weight loss are also what cause early nausea, so all three are started well below the therapeutic dose and held at each rung for weeks before climbing. Rushing the staircase is a common reason people abandon these drugs, which is why the schedule — not just the final number — is part of the dose.

Side-by-side: dosing at a glance

Property	Semaglutide	Tirzepatide	Retatrutide
Receptors	GLP-1	GIP + GLP-1	GIP + GLP-1 + glucagon
Starting dose	0.25 mg / wk	2.5 mg / wk	2 mg / wk (trial)
Top dose studied/approved	2.4 mg / wk	15 mg / wk	12 mg / wk (trial)
Typical step interval	4 weeks	4 weeks	4 weeks (trial)
Route	Subcutaneous	Subcutaneous	Subcutaneous
Approx. half-life	~7 days	~5 days	~6 days
Approval status	FDA approved	FDA approved	Investigational

Semaglutide and tirzepatide figures reflect the FDA-approved Wegovy and Zepbound labels for weight management. Retatrutide figures are from the Phase 2 obesity trial protocol, where doses were escalated over several weeks toward 1, 4, 8 or 12 mg targets; there is no approved retatrutide schedule. Compounded vials are drawn manually, so you calculate the draw volume yourself — always follow your prescriber and your own vial label.

The titration timelines, visualised

All three follow the same staircase shape — hold each rung, then step up — but on three different vertical scales.

How to turn any dose into syringe units

This is where most people get stuck. The milligram dose is not what you read on the syringe — you read units, and a U-100 insulin syringe has 100 units per 1 mL. So the conversion is always the same three steps: find the concentration (mg/mL), divide your dose by it to get mL, then multiply by 100 to get units. It is identical arithmetic for all three drugs.

Worked example 1 — semaglutide

A compounded vial labelled 2.5 mg/mL, prescribed dose 1 mg/week.

1 mg ÷ 2.5 mg/mL = 0.4 mL. 0.4 mL × 100 units/mL = 40 units.

Draw 40 units on a U-100 syringe.

Worked example 2 — tirzepatide

A vial reconstituted to 15 mg/mL, prescribed dose 7.5 mg/week.

7.5 mg ÷ 15 mg/mL = 0.5 mL. 0.5 mL × 100 units/mL = 50 units.

Draw 50 units — exactly half of a 1 mL syringe.

Worked example 3 — retatrutide

A vial at 20 mg/mL, a 4 mg target dose (a trial step).

4 mg ÷ 20 mg/mL = 0.2 mL. 0.2 mL × 100 units/mL = 20 units.

Draw 20 units on a U-100 syringe.

Worked example 4 — retatrutide, higher step

Same 20 mg/mL vial, an 8 mg target dose.

8 mg ÷ 20 mg/mL = 0.4 mL. 0.4 mL × 100 units/mL = 40 units.

Double the dose, double the units — concentration held constant.

Worked example 5 — same dose, weaker vial

The same 4 mg retatrutide dose, but from a 10 mg/mL vial: 4 ÷ 10 = 0.4 mL × 100 = 40 units.

Half the concentration, double the units — for the identical milligram dose. This is why “how many units” has no single answer without the vial strength.

Dose-to-units reference chart

Representative weekly doses for each drug, shown as units on a U-100 syringe at two common compounded concentrations. Confirm against your own vial label before drawing.

Dose	At 5 mg/mL	At 10 mg/mL
0.5 mg (sema)	10 units	5 units
2.4 mg (sema max)	48 units	24 units
5 mg (tirz)	100 units	50 units
10 mg (tirz)	— (over 1 mL)	100 units
4 mg (reta)	80 units	40 units
8 mg (reta)	— (over 1 mL)	80 units
12 mg (reta)	— (over 1 mL)	— (over 1 mL)

Notice how the higher-dose drugs run out of syringe room on a weak vial: any draw over 1 mL will not fit a standard U-100 syringe, so stronger vials are used for larger tirzepatide and retatrutide doses. If your calculated draw exceeds 1 mL, ask your pharmacy about a higher-concentration vial.

How this is calculated

Every figure here uses two facts only: a U-100 syringe holds 100 units per mL, and concentration is dose divided by volume. There is no drug-specific constant — the arithmetic is identical for semaglutide, tirzepatide, retatrutide, or any other vialled peptide, which is exactly why one method covers all three. The calculators on this site automate this and let you sanity-check the result against the chart above. None of this is medical advice; it is the maths behind a dose your prescriber sets, and for retatrutide it reflects trial protocols rather than an approved regimen.

Frequently asked questions

Is retatrutide just a stronger tirzepatide?

No. Retatrutide adds a third receptor target (glucagon) on top of the GIP and GLP-1 receptors that tirzepatide hits. It is a different molecule on its own dose scale, and it is still investigational — not an approved, more-potent version of tirzepatide.

Why is a 12 mg retatrutide dose not “5x” a 2.4 mg semaglutide dose?

Because each drug has its own potency and separately calibrated dose range. The milligram numbers live on different scales, so comparing them directly — or converting one to another by ratio — is meaningless.

Do I draw more units for retatrutide than for semaglutide?

Not necessarily. Units depend on the vial concentration, not the drug name. A 4 mg retatrutide dose from a 20 mg/mL vial is 20 units; a 2.4 mg semaglutide dose from a 5 mg/mL vial is 48 units. The stronger the vial, the fewer the units.

Can I map my semaglutide or tirzepatide dose onto retatrutide?

No. There is no validated milligram conversion between these drugs, and retatrutide has no approved dosing schedule. Any switch is a prescriber decision with its own starting dose and titration — do not translate one dose into another yourself.

Sources

This guide is for general educational purposes only and does not constitute medical advice. Always follow your prescriber’s specific instructions and consult a qualified clinician before changing any protocol.