A precise statement of what a trial is measuring, including how it handles participants who stop treatment. It determines which participants contribute to the headline figure.

Why do placebo groups lose weight?

Trial participation itself includes dietary and activity support, so the placebo arm typically shows 2–3% reduction.

Can I compare retatrutide's 28.3% with CagriSema's 22.7%?

Only indirectly. The durations differ, the populations differ and the estimands may differ. The comparison is suggestive, not precise.

GLP-1 & Incretin Science

How to Read a Weight-Loss Trial Result Properly

JMWritten & reviewed by Jack Muncaster · Founder, UK PeptidesLast reviewed 2026-08-233 cited sources

A weight-reduction percentage is uninterpretable on its own. The same trial can legitimately report two different figures depending on the estimand, and figures from different trials differ by population, duration, comparator and dropout rate before they differ by compound. Five checks make the numbers readable.

Key facts

Check 1: Which estimand — efficacy or treatment-policy
Check 2: Population — comorbidities change the result
Check 3: Duration — curves may not have plateaued
Check 4: Comparator — placebo or active
Check 5: Discontinuation rate, not just efficacy
Worked example: CagriSema 22.7% vs 20.4%, same trial

Estimands: the reason one trial reports two numbers

REDEFINE 1 reported both 22.7% and 20.4% mean reduction for CagriSema. Neither is wrong. The first is the efficacy estimand, describing participants who adhered to treatment. The second is the treatment-policy estimand, describing everyone randomised regardless of whether they continued. Efficacy answers 'how well does this work when taken'; treatment-policy answers 'what happens if we prescribe it'. Press coverage almost always quotes the larger figure without naming which it is.

Population changes the answer more than potency does

Retatrutide's TRIUMPH-1 reported 28.3% in a relatively uncomplicated obesity population. TRIUMPH-3, in adults with severe obesity and established cardiovascular disease, reported up to 22.6%. Same compound, same sponsor, similar duration — the gap is population, not potency. Comparing a figure from a healthy-cohort trial against one from a comorbid cohort tells you almost nothing about the compounds.

Duration, and whether the curve had flattened

A percentage is meaningless without its timepoint, and a timepoint is more informative when you know whether reduction had plateaued. Amycretin's Phase 2 reported that at higher doses no plateau had been reached by week 36, which means the figure reflects the trial's length. A trial that stops while the curve is still descending reports a floor for that duration; one that ran past plateau reports something closer to a ceiling.

Discontinuation belongs next to efficacy

TRIUMPH-1 reported 11.3% discontinuation due to adverse events on the 12 mg arm against 4.9% on placebo. That figure is routinely dropped from summaries, and it is exactly the number that connects to the estimand question — the people who discontinue are the difference between the two headline percentages. A compound with a larger effect and a much higher dropout rate is not straightforwardly better.

Placebo response is not zero

Placebo arms in these trials typically show 2–3% reduction, because trial participation itself involves dietary and activity counselling. Some summaries quote absolute reduction and others quote placebo-adjusted reduction, and the difference is a couple of percentage points. Amycretin's Phase 2, for instance, was reported as 11.9% placebo-adjusted for the subcutaneous arm rather than as an absolute figure.

A checklist

Before comparing any two figures, confirm they match on the following. If they do not, the comparison is indirect at best.

Same estimand — efficacy or treatment-policy
Comparable population and baseline BMI
Same or similar duration, and whether the curve plateaued
Same comparator, and whether the figure is placebo-adjusted
Discontinuation rates reported alongside efficacy

Extended research context

The GLP-1 & Incretin Science deep dive

Deep dive: the two routes to a bigger effect

Every compound trying to beat GLP-1 alone has taken one of two routes. The first adds more receptors from the same hormone family — GIP in tirzepatide, GIP and glucagon in retatrutide. The second adds a non-incretin satiety hormone, which in practice means amylin: CagriSema combines cagrilintide with semaglutide, and amycretin engages both receptors from one molecule. Both routes work, because they recruit signalling pathways that do not fully overlap. Neither has escaped the constraint that binds all of them, which is that gastrointestinal tolerability worsens as effect size grows.

Deep dive: why a percentage is not a result

The most-quoted numbers in this field are the least comparable. REDEFINE 1 reported 22.7% and 20.4% for the same compound in the same trial — the first among participants who adhered to treatment, the second across everyone randomised. TRIUMPH-1 reported 28.3% in an uncomplicated obesity population while TRIUMPH-3 reported up to 22.6% in adults with established cardiovascular disease, using the same compound. Before any two figures can be compared they have to match on estimand, population, duration, comparator and whether the number is placebo-adjusted. Most published comparisons match on none of them.

Deep dive: what happens after the trial stops

Every headline figure describes weight while treatment continues. The STEP-1 extension found that a year after semaglutide was stopped, participants had given back roughly two-thirds of what they lost, moving from 17.3% mean reduction to a net 5.6% — though average weight remained below baseline and nearly half stayed at least 5% down. Meta-analysis puts regain at around 0.8 kg per month. This is why maintenance studies such as TRIUMPH-6 matter more to the field's future than another two points of peak reduction.

Research applications

▸Comparing incretin and amylin compounds on a like-for-like basis
▸Interpreting estimands, thresholds and placebo-adjusted figures in trial reports
▸Tracking the obesity pipeline across sponsors and jurisdictions
▸Understanding receptor pharmacology behind GLP-1, GIP, glucagon and amylin
▸Distinguishing licensed medicines from investigational compounds

Handling checklist

✓Identify which estimand a quoted percentage comes from before citing it
✓Check the trial population and baseline BMI against the comparison you are making
✓Confirm the duration and whether the reduction curve had plateaued
✓Read discontinuation rates alongside efficacy figures
✓Verify every NCT identifier against ClinicalTrials.gov rather than secondary reporting

Common research-handling mistakes

Learnt from thousands of researcher orders across our UK labs.

✗ Comparing headline percentages across different trials

Fix: Population, duration, estimand and comparator all differ; the numbers are not interchangeable.

✗ Quoting the larger of two figures from the same trial

Fix: Name the estimand. Efficacy and treatment-policy answer different questions.

✗ Treating peak reduction as a durable outcome

Fix: Substantial regain follows cessation across the class; peak figures describe a maintained state.

✗ Assuming an oral route means a weaker mechanism

Fix: Route and receptor count are independent. Orforglipron is weaker because it hits one receptor, not because it is a tablet.

✗ Reading investigational compounds as available treatments

Fix: Most of this pipeline holds no authorisation anywhere; mazdutide is approved only in China.

Continue researching

Peer-reviewed guides, comparators and matched reference materials.

Frequently asked questions

What is an estimand?: A precise statement of what a trial is measuring, including how it handles participants who stop treatment. It determines which participants contribute to the headline figure.
Why do placebo groups lose weight?: Trial participation itself includes dietary and activity support, so the placebo arm typically shows 2–3% reduction.
Can I compare retatrutide's 28.3% with CagriSema's 22.7%?: Only indirectly. The durations differ, the populations differ and the estimands may differ. The comparison is suggestive, not precise.

Primary sources & clinical trials

Peer-reviewed research and registered trials from PubMed, ClinicalTrials.gov, PubChem, FDA and NIH. All links open in a new tab and point to the primary source, so every claim can be verified at origin.

Written and reviewed by

Jack Muncaster · Founder, UK Peptides

Jack founded UK Peptides in Manchester after repeatedly receiving research compounds with missing or recycled paperwork. He is responsible for supplier selection, batch release decisions and the content published in this research library. Every article here is sourced to primary literature and every product page to a signed third-party certificate.

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