Retatrutide Before and After: The Week-by-Week Timeline From Phase 2 and the 2026 TRIUMPH Data

Retatrutide has the steepest published weight curve of any compound the Bureau covers, and as of September 2026 it has the data to back it: a 338-person phase 2 trial in the New England Journal of Medicine with a 48-week endpoint, and four phase 3 TRIUMPH trials with topline results released by Eli Lilly between December 2025 and July 2026. That is more than 6,000 participants measured at fixed timepoints. A "before and after" for retatrutide can therefore be built from least-squares means rather than from anyone's mirror.

This page sets out what those trials say happens week by week, what a researcher should record before the first dose so the "after" is interpretable, how big the real change is against ordinary weight noise, where the plateau sits, what comes back when the compound is stopped, and where people misread the result. For the pharmacology, see the Bureau's retatrutide guide.

Where the before-and-after data come from

The phase 2 obesity trial randomised 338 adults with a BMI of 30 or more (or 27 with a weight-related condition) to once-weekly retatrutide at 1, 4, 8 or 12 mg, or placebo, for 48 weeks, with the primary endpoint at 24 weeks. A parallel phase 2 trial in 281 people with type 2 diabetes ran to 36 weeks. The phase 1b study established a half-life of about six days, and the single-dose study found weight reduction persisting to day 43 after one injection.

The phase 3 programme is what changed in 2026. TRIUMPH-4 (445 adults with knee osteoarthritis, 68 weeks) reported in December 2025. TRIUMPH-1 (2,339 adults, 80 weeks, with a 104-week extension) reported on 21 May 2026. TRIUMPH-2 (1,152 adults with type 2 diabetes) and TRIUMPH-3 (1,949 adults with severe obesity and cardiovascular disease) reported together on 23 July 2026. All are company topline releases rather than peer-reviewed papers, so the numbers below are Lilly's, and the full adverse-event tables are not yet public.

What is missing: no retatrutide trial has published a withdrawal phase. For what happens after stopping, this page uses the semaglutide and tirzepatide withdrawal data, which are the closest evidence available, and says so.

The week-by-week timeline

Two features of the curve deserve a sentence each. First, the 24-week and 48-week numbers are not the same: on 12 mg the loss went from 17.5% to 24.2%, so the "after" at six months understates the compound by about a third. Second, the 8 mg and 12 mg arms were nearly identical at 24 weeks (17.3% versus 17.5%) and only separated by 48 weeks, which means dose escalation beyond 8 mg buys its extra effect late and at the price of the GI numbers below.

What to record before the first dose

Retatrutide's effect is large enough to see without instruments. The baseline matters for a different reason: separating fat from lean tissue, catching the cardiovascular and GI signals, and knowing what you are trying to keep when the compound stops.

• Seven-day average scale weight, fasted, same time. The first fortnight's loss is partly gut contents and water; a rolling average is the only way to see the underlying rate.
• Waist at the navel and hip circumference, three readings averaged. In the semaglutide DEXA substudy, visceral fat fell 27.4% against a 15% weight loss, so waist tends to move faster than weight.
• A DEXA or at least a grip-strength test and a photograph of the arms. In the semaglutide substudy, lean body mass fell 9.7% while total weight fell 15%; roughly 40% of the kilograms lost were lean. No retatrutide-specific body-composition data are published. Researchers who want to know how much of their loss was muscle need a baseline scan.
• Resting heart rate, morning, seated, averaged over a week. The phase 2 trial found dose-dependent increases peaking at 24 weeks then declining.
• Fasting glucose and HbA1c. Retatrutide lowered HbA1c by up to 2.02% at 24 weeks in the diabetes phase 2 trial. A non-diabetic researcher will not see that, but hypoglycaemia symptoms with a fasted training session are worth understanding against a baseline.
• Photographs: front, side, back, same light, same distance, weekly, including the face. The Ozempic face page explains why facial fat loss is the change people notice first and dislike most.
• A food and GI log: what was eaten, nausea by day, bowel habit. In TRIUMPH-1, nausea occurred in 42.4% of the highest-dose group and diarrhoea in 32.0%; in TRIUMPH-4, vomiting in 20.4% to 20.9% and dysesthesia (abnormal skin sensation) in 8.8% to 20.9% versus 0.7% on placebo.
• Hair density photographs of the scalp, because rapid weight loss itself causes shedding. See retatrutide and hair loss.

Realistic magnitude, and what is noise

The realistic magnitude is the largest of any injectable compound the Bureau covers: 17% to 24% in a year at 8 to 12 mg in the phase 2 trial, and 26% to 30% at 68 to 104 weeks in phase 3. In TRIUMPH-1, 45.3% of the 12 mg group lost 30% or more of their body weight, a figure the company compared to bariatric surgery. The placebo groups lost about 2%.

Three things temper it. The trial populations were enrolled for obesity (a BMI of 30 or more in phase 2, severe obesity in TRIUMPH-3); percentages are of a large starting weight, and a researcher at BMI 27 has less to lose and will lose less. The phase 3 numbers are company toplines on the "efficacy estimand", which counts people who stayed on treatment; the treatment-regimen figures that include dropouts will be lower when published. And discontinuation for adverse events was not trivial: 11.3% on 12 mg in TRIUMPH-1 versus 4.9% on placebo, 18.2% on 12 mg in TRIUMPH-4, 11.6% on 9 mg in TRIUMPH-2.

Noise is small relative to this signal but not zero. Daily weight varies by 1 to 2 kg; against a 0.4 to 0.6 kg weekly loss that is why single readings mislead in the first month. The bigger source of error is the plateau question. Researchers who stall at week 20 often assume the compound has stopped working. The phase 2 data say the curve is still falling at 48 weeks on every dose; a stall at 20 weeks in an individual is more likely the titration schedule, food intake creeping back, or a measurement artefact than a ceiling.

What reverses on stopping

No retatrutide withdrawal data have been published. The closest evidence is the class. In the STEP 1 extension, 327 participants who stopped semaglutide 2.4 mg after 68 weeks regained 11.6 percentage points of a 17.3% loss over the following year, two-thirds of it, and cardiometabolic markers reverted with the weight. In SURMOUNT-4, participants switched to placebo after 36 weeks of tirzepatide regained 14.0% from that point over 52 weeks while those who continued lost a further 5.5%; only 16.6% of the placebo group kept 80% of their loss, against 89.5% who stayed on treatment.

Retatrutide adds glucagon-receptor agonism to the GIP and GLP-1 mechanisms, and the glucagon component is thought to raise energy expenditure. Whether that changes the regain curve is unknown; the mechanism gives no reason to expect a lasting reset, and the six-day half-life means the appetite effect is gone within a few weeks of the last dose. The peptide cycles page covers how researchers taper compounds whose effect is entirely on-treatment.

Where people misattribute results

The first fortnight's loss as fat. Reduced food volume, slower gastric emptying and the diarrhoea that 24% to 34% of phase 3 participants reported all remove weight that is not adipose tissue. The rolling average and the tape catch up by week four.

All the loss as fat. The class data say roughly 40% of kilograms lost on a GLP-1 agonist are lean mass, unless resistance training and protein intake are protected. A DEXA before and at 12 weeks is the only way to know your own ratio.

A stall as the ceiling. See above: the trials did not plateau at 24 or 48 weeks. Individual stalls are usually intake, titration or water.

Dose as the driver. At 24 weeks, 8 mg and 12 mg were separated by 0.2 percentage points. The GI and discontinuation numbers, by contrast, rose sharply with dose. The trial data reward patience at a tolerable dose more than escalation.

Comparing to tirzepatide by the headline. The tirzepatide versus retatrutide page sets the curves side by side; the trials differ in duration, population and dose schedule, and a straight comparison of 48-week phase 2 to 72-week phase 3 flatters retatrutide.

The face. Loss of facial fat and the sagging that follows rapid weight loss are frequently blamed on the compound rather than on the speed. Any 25% weight loss does this.

Sourcing and dosing notes

The trials used 2 mg starting doses escalated every four weeks to 4, 8, 9 or 12 mg once weekly. Research protocols mirror that, and the retatrutide dosage guide walks through the arithmetic. The retatrutide dosage calculator converts a vial size and water volume into syringe units, and the retatrutide titration schedule lays out the four-week steps.

On sourcing: because the phase 3 discontinuation rates were driven by GI effects at the top doses, dose accuracy and a clean vial matter more here than with most compounds. The Bureau's top-scored source for retatrutide-class compounds at the time of writing is Apollo Peptide Sciences, which publishes a batch certificate of analysis on the product page and ships from the US; it sells the compound under a coded name, GLP-3 R, that its listing identifies as retatrutide. Check price at Apollo Peptide Sciences The retatrutide where-to-buy guide sets out the alternatives, and how to reconstitute retatrutide covers handling.

Retatrutide is an investigational compound that is not approved anywhere as of September 2026. The trial figures above come from supervised studies in people enrolled for obesity; nothing here is medical advice, and the Bureau does not advise anyone on using research compounds.

Frequently Asked Questions

How much weight do people lose on retatrutide, and how fast?

In the phase 2 trial, least-squares mean loss at 24 weeks was 12.9% on 4 mg, 17.3% on 8 mg and 17.5% on 12 mg, rising to 17.1%, 22.8% and 24.2% at 48 weeks, against about 2% on placebo. Phase 3 toplines in 2026 report 28.3% at 80 weeks on 12 mg in TRIUMPH-1 and 30.3% at 104 weeks. The curve was still falling at 48 weeks in phase 2, so the six-month figure understates the compound by roughly a third.

When does retatrutide plateau?

Later than most researchers expect. The 48-week phase 2 curve had not flattened on any dose, and the phase 3 figures show continued, slower loss between 68 and 104 weeks. An individual stall at 16 to 24 weeks is more likely to be the titration schedule, food intake creeping back, or water and gut-content variation than a ceiling. Track a seven-day rolling average rather than single readings and compare against the previous month, not the previous week.

What are the most common retatrutide side effects and when do they start?

Gastrointestinal, from the first weeks and clustering around each dose step. In TRIUMPH-1 at the highest dose, nausea occurred in 42.4% and diarrhoea in 32.0% versus 14.8% and 13.5% on placebo; TRIUMPH-4 reported vomiting in about 20% and dysesthesia in 8.8% to 20.9%. Heart rate rose dose-dependently, peaking at week 24 in phase 2. Discontinuation for adverse events was 11.3% on 12 mg in TRIUMPH-1 and 18.2% in TRIUMPH-4. Starting at 2 mg rather than 4 mg partially reduced GI events.

How much of retatrutide weight loss is muscle?

No retatrutide body-composition data are published. In the semaglutide STEP 1 DEXA substudy, lean body mass fell 9.7% while total weight fell 15%, so roughly 40% of the kilograms lost were lean tissue, although the lean proportion of body weight rose. Researchers who want their own figure need a DEXA before the first dose and again at 12 weeks, plus protein intake and resistance training logged from the start. Grip strength is a cheap proxy.

Does the weight come back after stopping retatrutide?

There are no retatrutide withdrawal data yet. In the closest class evidence, people who stopped semaglutide after 68 weeks regained two-thirds of their loss within a year, and people switched from tirzepatide to placebo regained 14% of body weight over 52 weeks while only 16.6% kept 80% of their loss. Retatrutide's six-day half-life means appetite effects fade within weeks of the last dose, and nothing in its mechanism suggests a lasting reset.

Does a higher retatrutide dose mean better results?

Not proportionally. At 24 weeks in phase 2, 8 mg and 12 mg produced 17.3% and 17.5% loss, a difference of 0.2 points; they only separated by 48 weeks (22.8% versus 24.2%). Adverse-event discontinuation, by contrast, rose steeply with dose in every phase 3 trial. The trial data favour staying at a tolerable dose for longer over escalating to the maximum, and a 2 mg start reduced GI events compared with a 4 mg start.

What should I measure before starting retatrutide?

A seven-day fasted weight average, waist and hip circumference, resting heart rate averaged over a week, fasting glucose and HbA1c, a DEXA or at least grip strength for lean mass, standardised photographs including the face and scalp, and a food and GI symptom log. The heart-rate and lean-mass baselines are the ones most researchers skip and most regret, because the phase 2 heart-rate rise and the class lean-mass loss are invisible without a starting number.

Research use only. The compounds discussed are sold as research chemicals and are not approved for human use. Nothing here is medical advice.