Retatrutide vs Tirzepatide: dosage chart and what it really tells you

The biggest myth: retatrutide is just a stronger Mounjaro

The most common misconception circulating on weight-loss forums is that retatrutide is essentially a higher-dose or next-generation version of tirzepatide, with a dosage chart you can simply read across from one to the other. That framing is wrong in two important ways.

First, the mechanisms differ. Tirzepatide activates two receptors (GIP and GLP-1) making it the only dual-agonist currently licensed in the UK for weight management. Retatrutide activates three: GIP, GLP-1 and glucagon receptors. Whether that additional pathway translates into meaningfully better outcomes at approved doses is still being tested; phase-three data are not yet published, and no regulator has reviewed them. The NHS tirzepatide medicines page gives a clear account of how the dual-agonist mechanism works if you want the clinical background.

Second, the trial doses for retatrutide (up to 12 mg weekly in phase two) look superficially close to tirzepatide's 15 mg ceiling, but dose numbers across different molecules are not directly comparable. Potency, receptor binding affinity and tolerability profiles differ compound by compound. A chart that lines up 12 mg retatrutide against 15 mg Mounjaro implies an equivalence that the science does not support at this stage. If you are considering a move between these treatments, our page on switching from Mounjaro to retatrutide dosage explains why that transition is not as straightforward as a simple dose conversion. The only honest comparison is: one medicine has a licensed UK dosage schedule; the other does not.

Tirzepatide's licensed UK dosage schedule, the facts

Because tirzepatide is the approved option, its dosing is worth setting out clearly. Treatment starts at 2.5 mg weekly; the first pen's purpose is letting your system adjust, not producing therapeutic weight loss from week one. The schedule typically moves through 5 mg, 7.5 mg, 10 mg, 12.5 mg and 15 mg in roughly four-week steps, guided entirely by your prescriber based on tolerability and clinical review. For a detailed breakdown of how those steps work in practice, the tirzepatide dosage chart on this site covers the full licensed schedule.

NICE recommends tirzepatide for adults with a BMI of 35 or above plus at least one weight-related condition, with lower BMI thresholds applicable for South Asian, Chinese, Middle Eastern, Black African or African-Caribbean backgrounds under NICE appraisal TA1026. Private prescribing through a regulated pharmacy like nume can cover adults with BMI 30 or above, or 27 and above with a relevant condition, a prescriber assesses the full picture, not the number alone.

Retatrutide has no licensed schedule to describe, because there is none. Any figure you read online reflects a clinical trial protocol, not an approved treatment plan.

Head-to-head comparison: what we can and cannot say

The table below places the two compounds side by side on verifiable facts. Where a cell contains "not yet established", that is the accurate answer, not a gap in research.

The SURMOUNT-1 trial randomised 2,539 adults with obesity and reported average reductions of around 20–21% of body weight at the 15 mg dose over 72 weeks. That is the evidence base for tirzepatide. Retatrutide's phase-two results attracted attention (some participants in a small trial lost around 17% at 24 weeks at the highest doses) but 24 weeks is not 72 weeks, phase two is not phase three, and phase three is not a licence. Parallel comparison charts built from those numbers are premature.

If you want to read more about where the two compounds sit side by side from a clinical-access perspective, the retatrutide vs Mounjaro dosage page goes deeper on what the current trial data do and do not show.

What this means practically, and where to go from here

If you are researching retatrutide because tirzepatide's results have caught your attention but you want to know whether something better is coming, that is a reasonable question. The clinical answer today is: tirzepatide is available, its evidence is robust, and retatrutide may reach regulators in a few years if trials go well. "May" is doing real work in that sentence.

If you are already on tirzepatide and thinking about where higher doses fit, the 10 mg dosage guide covers that part of the schedule in practical detail, and our prescribers review dose progression at every repeat order.

At nume, our clinical team reviews every consultation personally, a real prescriber reading your answers, checking your Summary Care Record where appropriate and confirming clinical suitability before any prescription is issued. If approved, your Mounjaro pen ships the same day and arrives via DPD the next working day: tracked to your phone, in a plain box, cold-chain intact. Nothing about retatrutide is available to prescribe yet. Tirzepatide is.

For a broader look at Mounjaro and how it works, or to check the current treatment pricing, those pages have the detail. When you are ready to find out whether you are clinically suitable, start your free consultation, which medicine fits your situation is a clinical decision our prescribers make with you.