Semaglutide vs Retatrutide Dosing Compared

Last updated: June 2026

Semaglutide and retatrutide are both once-weekly subcutaneous injections, but they sit on different scales and different stages of development: semaglutide is FDA-approved and titrates 0.25 → 2.4 mg weekly, while retatrutide is an investigational triple-receptor agonist studied at up to 12 mg weekly. They are not interchangeable milligram-for-milligram, and the syringe units you draw depend on your vial concentration — not on which drug it is.

Reconstituted a retatrutide vial and need to know the draw? Convert any weekly dose to exact mL and U-100 syringe units in seconds.

Retatrutide calculator →

TL;DR — key takeaways

Different approval status. Semaglutide is FDA-approved (Ozempic, Wegovy). Retatrutide is not approved for any use — it is in phase 3 trials, so any non-trial supply is unregulated.
Different mechanism. Semaglutide hits one receptor (GLP-1); retatrutide is a triple agonist hitting GIP, GLP-1, and glucagon receptors.
Different number lines. Semaglutide tops out at 2.4 mg/week for weight management; retatrutide was studied up to 12 mg/week. A 2.4 mg dose is not "weak" — the molecules use different ranges.
Units follow concentration. Whether you draw 10, 40, or 100 units depends on the mg/mL strength of your vial, which is what a reconstitution or units calculator works out for you.

Why the two dose scales look so different

Semaglutide is a glucagon-like peptide-1 (GLP-1) receptor agonist. It mimics the GLP-1 hormone to promote glucose-dependent insulin release, slow gastric emptying, and blunt appetite. Retatrutide is a single molecule that activates three receptors at once: the GLP-1 receptor, the glucose-dependent insulinotropic polypeptide (GIP) receptor, and the glucagon receptor. The glucagon-receptor arm is the headline difference — it is thought to raise energy expenditure on top of the appetite effects shared with GLP-1 drugs.

Because retatrutide recruits three pathways with different potencies, its effective milligram range is not aligned with semaglutide's. You cannot assume "1 mg of one equals 1 mg of the other." In its phase 2 obesity trial, retatrutide at 12 mg once weekly produced a mean weight reduction of about 24% at 48 weeks; semaglutide 2.4 mg in the STEP 1 trial produced about 15% over 68 weeks. Those are different molecules, different doses, and different trial designs — useful context, not a head-to-head conversion.

Both are dosed once weekly because both clear slowly: semaglutide has an elimination half-life of roughly seven days, and retatrutide's supports weekly injection as well. Steady state is reached only after several weeks, which is the same window over which the dose is being stepped up.

The honesty caveat: retatrutide is investigational

This matters enough to repeat. As of 2026 retatrutide has no FDA-approved label, no approved indication, and no standardised consumer dosing. Every dose figure below comes from published clinical trials, not from a prescribing label, and trial protocols are run under medical supervision with pharmaceutical-grade drug. "Research" or compounded retatrutide sold outside a trial is not quality-controlled, and its true concentration may not match the label. Treat the trial doses as background information, not a protocol to copy. Semaglutide, by contrast, has full FDA labels you can read directly.

Side-by-side: dosing at a glance

Property	Semaglutide	Retatrutide
Class	GLP-1 receptor agonist	GIP + GLP-1 + glucagon triple agonist
Approval status	FDA-approved (Ozempic, Wegovy)	Investigational — phase 3 ongoing
Trial starting dose	0.25 mg / week	~2 mg / week (trial)
Step interval	4 weeks	~2–4 weeks (trial protocols)
Top studied/maintenance	2.4 mg / week (Wegovy)	12 mg / week (phase 2)
Route	Subcutaneous, once weekly	Subcutaneous, once weekly
Approx. half-life	~7 days	~6 days

Semaglutide figures reflect the FDA-approved Wegovy and Ozempic labels. Retatrutide figures reflect the phase 2 obesity and type 2 diabetes trials; phase 3 schedules may differ. Always follow the protocol set by the supervising clinician.

The titration timeline, visualised

Both drugs follow the same staircase shape — start low, hold each rung for several weeks, climb slowly to let gastrointestinal side effects settle — but on very 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. 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. The drug name never enters the maths.

Worked example 1 — semaglutide start

A compounded vial labelled 2.5 mg/mL, prescribed dose 0.25 mg/week.

0.25 mg ÷ 2.5 mg/mL = 0.1 mL. 0.1 mL × 100 units/mL = 10 units.

Draw 10 units on a U-100 syringe.

Worked example 2 — semaglutide maintenance

A vial at 4 mg/mL, prescribed dose 1 mg/week.

1 mg ÷ 4 mg/mL = 0.25 mL. 0.25 mL × 100 units/mL = 25 units.

Draw 25 units — a quarter of a 1 mL syringe.

Worked example 3 — retatrutide reconstitution

A 10 mg lyophilised retatrutide vial reconstituted with 1 mL bacteriostatic water gives 10 mg/mL. Trial-level dose 4 mg/week.

4 mg ÷ 10 mg/mL = 0.4 mL. 0.4 mL × 100 = 40 units.

Draw 40 units on a U-100 syringe.

Worked example 4 — retatrutide top dose

A vial reconstituted to 20 mg/mL, trial-level dose 12 mg/week.

12 mg ÷ 20 mg/mL = 0.6 mL. 0.6 mL × 100 = 60 units.

Draw 60 units on a U-100 syringe.

Worked example 5 — same dose, different concentration

The same 4 mg retatrutide dose from a 20 mg/mL vial: 4 ÷ 20 = 0.2 mL × 100 = 20 units.

That is half the units of Example 3 for the identical milligram dose — because the vial is twice as strong.

Worked example 6 — when the draw won't fit

An 8 mg retatrutide dose from a weak 5 mg/mL vial: 8 ÷ 5 = 1.6 mL — more than a 1 mL syringe holds.

Use a higher-concentration vial so larger doses fit one injection.

Dose-to-units reference chart

Common weekly doses for each drug, shown as units on a U-100 syringe at two typical compounded concentrations. Always confirm against your own vial label.

Dose	At 10 mg/mL	At 20 mg/mL
0.25 mg (sema start)	2.5 units	1.25 units
1 mg (sema)	10 units	5 units
2.4 mg (sema max)	24 units	12 units
2 mg (reta start)	20 units	10 units
4 mg (reta)	40 units	20 units
8 mg (reta)	80 units	40 units
12 mg (reta max)	— (over 1 mL)	60 units

Notice the gap at 12 mg / 10 mg/mL: that draw is 1.2 mL, more than a standard 1 mL syringe holds, so a stronger vial is used for larger retatrutide doses. If your draw exceeds 1 mL, the concentration is too low for that dose.

How this is calculated

Every figure here uses two facts only: a U-100 syringe holds 100 units per mL, and concentration is dose-per-volume. There is no drug-specific constant — the arithmetic is identical for semaglutide, retatrutide, or any other vialled peptide. The calculators on this site automate exactly 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 or trial protocol has set, and for retatrutide there is no approved dose to set in the first place.

Frequently asked questions

Is retatrutide just a stronger semaglutide?

No. Retatrutide activates three receptors (GIP, GLP-1, and glucagon) while semaglutide activates one (GLP-1). The added glucagon-receptor activity is a different mechanism, not simply a higher dose of the same thing, so the milligram scales do not line up.

Can I buy retatrutide at a pharmacy?

Not as an approved medicine. Retatrutide is still in clinical trials and has no FDA approval, so it is only available through a study. Any other source is unregulated, and its real concentration and purity are not guaranteed.

Do I draw more units for retatrutide than semaglutide?

Usually yes, because retatrutide doses are larger in milligrams — but units still depend on 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 10 mg/mL vial is 24 units.

Why does 2.4 mg sound small for semaglutide but 12 mg is normal in retatrutide trials?

Each molecule has its own potency and dose range. 2.4 mg is the maximum weight-management maintenance dose for semaglutide; 12 mg was the top dose in the retatrutide phase 2 obesity trial. Comparing the raw numbers across drugs is meaningless.

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.