Dosing & Usage

Retatrutide Dosing Guide

Learn the expected Retatrutide dosing schedule based on clinical trials, including starting dose, escalation, and what to expect when it becomes available.

Whether you have read about retatrutide and want to understand the dosing schedule used in trials, or are following its development towards possible approval, this guide explains the dosing tested in the published phase 2 obesity trial — and why no UK dosing schedule exists outside that trial. LetsLoseWeight is an independent comparison site; we do not prescribe medication.

Important: Retatrutide is an investigational medicine. As of this guide's last review, it is not licensed by the MHRA and is not available from any regulated UK pharmacy. There is therefore no licensed UK dosing schedule for retatrutide. The doses described below are from clinical trials and should not be used as a self-administration guide. Anyone offering retatrutide for sale in the UK outside a registered clinical trial is doing so unlawfully.

Why there is no licensed UK schedule

A licensed dosing schedule for any prescription medicine in the UK requires:

  1. Phase 3 clinical trials producing data to support specific doses
  2. MHRA marketing authorisation confirming the doses are safe and effective for a defined indication
  3. A Summary of Product Characteristics (SmPC) specifying dosing, titration, contraindications, and warnings
  4. Patient information leaflets with patient-facing dosing instructions

Retatrutide has none of these in the UK. Phase 3 trials (the TRIUMPH programme) are ongoing. Until they complete and the MHRA reviews them, no licensed schedule exists.

This is the same status as for any unapproved prescription medicine — not a temporary gap or oversight, but the ordinary process of medicine approval working as designed.

What the phase 2 trial used

The retatrutide phase 2 obesity trial published in the New England Journal of Medicine in 2023 tested several dose levels alongside a titration schedule (Jastreboff et al., NEJM 2023). The doses studied:

Dose Average weight loss at 48 weeks
1mg weekly ~8.7%
4mg weekly ~17.1%
8mg weekly ~22.8%
12mg weekly ~24.2%

The trial protocol included a graduated titration to reach each target dose, similar in principle to Mounjaro and Wegovy titration but with different specifics for each dose group. The titration approach was used to reduce gastrointestinal side effects that, like other GLP-1-class medicines, are most pronounced when starting and at dose increases.

These doses were chosen for the trial — they are not licensed maintenance doses. Phase 3 trials may explore the same doses, narrower ranges, or different titration approaches.

What "trial dose" doesn't mean

Trial doses are research-grade and trial-controlled. They are not a self-administration guide because:

  • Trial doses are administered to selected trial populations with specific eligibility, screening, and exclusions
  • Trial doses are paired with controlled titration monitored by clinical staff
  • Trial doses are accompanied by safety monitoring including blood tests, ECGs, and frequent clinical review
  • Trial product is supplied by the manufacturer with verified composition and consistency

The product available from unregulated sellers carries none of these safeguards. The vials may not contain retatrutide, may be incorrectly dosed, or may be contaminated. The "12mg weekly" trial dose has no meaningful relationship to whatever an unregulated seller is offering.

Why the trial schedule is not safe to follow at home

A patient cannot replicate trial conditions at home. Specifically:

  • No clinical assessment — contraindications (likely including MTC, MEN 2, pancreatitis, pregnancy) cannot be screened for
  • No dose verification — there is no way to confirm what is in an unregulated vial
  • No safety monitoring — phase 2 trial participants had blood tests checking for cardiac, liver, pancreatic and other markers
  • No emergency protocol — if something goes wrong, there is no clinical team to escalate to
  • No regulator oversight — adverse events are not collected and analysed

Even if you could obtain trial-grade product (which is not legally possible outside a registered trial), administering it without the supporting clinical infrastructure is unsafe.

What the licensed schedule will likely look like

Drawing on the trial design and on parallels with Mounjaro and Wegovy, the eventual licensed retatrutide schedule will probably involve:

  • A starter dose below the weight-loss threshold (similar to Mounjaro 2.5mg or Wegovy 0.25mg)
  • Step-ups every 4 weeks, with patient-by-patient flexibility on pacing
  • Multiple maintenance dose options so patients can settle at a tolerable level
  • A maximum licensed dose below which prescribers may not exceed
  • Specific contraindications and warnings, likely including MTC/MEN 2 (as for the rest of the GLP-1 class)
  • Pregnancy and breastfeeding contraindications
  • A black triangle (▼) for additional safety monitoring during the first years post-licensing

This is reasonable expectation, not regulatory guidance. The actual schedule will only be known after MHRA approval.

What changes when retatrutide is licensed

If the TRIUMPH trials succeed and retatrutide is approved for UK use:

  • GPhC-registered UK pharmacies will offer it through the same online clinical assessment process used for Mounjaro and Wegovy
  • A specific dose schedule will be published in the SmPC and patient information leaflet
  • A specific maximum dose will be set
  • NICE technology appraisal will determine NHS access criteria
  • This site will list regulated UK providers and dose schedules as they become available

Until any of those happen, the "dosing guide" for retatrutide is the trial paper — useful for understanding the medicine's potential but not a self-administration guide.

What to do instead, if dosing-related questions matter to you

If you are interested in retatrutide because of its dosing characteristics or weight-loss profile:

Use a currently licensed alternative

Mounjaro and Wegovy are licensed in the UK with established dosing schedules. Mounjaro in particular has shown the largest average weight loss of any currently licensed weight-management medicine.

Take part in a clinical trial

The TRIUMPH trial programme is recruiting in some countries. For UK trial sites, see the National Institute for Health and Care Research's Be Part of Research portal. Trial participation includes:

  • Free participation
  • Detailed clinical assessment
  • Trial-grade product
  • Safety monitoring
  • Follow-up care

This is the only legitimate way to access retatrutide in the UK at this time.

Wait for MHRA approval

There is no published date. Anyone considering weight-loss treatment now should focus on the medicines actually available through regulated UK channels.

Frequently asked questions

Can I work out what dose to take based on the trial?
No — and you shouldn't try. Trial doses were administered with full clinical assessment, monitoring, and trial-grade product. None of that applies to whatever is being sold outside trials.

What's the highest tolerated dose in the phase 2 trial?
12mg weekly produced the largest average weight loss (~24%), but with greater rates of gastrointestinal side effects than lower doses. The phase 2 trial was not designed to identify a single optimal dose — phase 3 trials will refine the dose range.

How is retatrutide dosing different from Mounjaro?
Mounjaro doses are 2.5mg–15mg weekly. Retatrutide doses in phase 2 were 1mg–12mg weekly. The numbers are not directly comparable because the medicines have different potencies and target different combinations of receptors. Mounjaro acts on GIP and GLP-1; retatrutide adds glucagon receptor activation.

Will the licensed schedule match the trial?
Possibly with adjustments. Phase 3 trials may identify a narrower dose range as optimal, or alter the titration schedule based on what works best in larger populations. The licensed SmPC will be the definitive guide.

Is retatrutide more potent than Mounjaro at the same number?
Not directly comparable — they are different molecules with different receptor activity profiles. The phase 2 trial figures show greater average weight loss at the highest dose than Mounjaro's pivotal trial, but this is across separate trials with different protocols and durations.

Next steps

Sources

This guide is for general information only. Retatrutide is not currently approved or available in the UK outside clinical trials. Trial doses described above are not a self-administration guide.

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Retatrutide Dosing Guide: Trial Doses Explained UK | LetsLoseWeight