The short answer: in Lilly's trials, retatrutide didn't stop working. Weight loss was fastest in the first six months and slowed after that, but it was still going at 48 weeks in phase 2 and, for one group, at 104 weeks in phase 3.
What does fade, on every drug in this family, is how strongly you feel it. Studies show appetite pushes back as weight comes off, and the "I'm not hungry" feeling can wear off even while the drug is still cutting what people eat. Add the fact that a research-use vial isn't Lilly's product, and there are three separate explanations that feel exactly the same from the inside.
Status as of October 30, 2026: Retatrutide is not approved by the FDA or any regulator. Lilly plans to file for U.S. approval in Q1 2027. Every trial number below is from Lilly's own drug at known doses, under medical supervision. Nothing here is medical advice or a dosing guide.
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Why did reta stop working?
Nobody has studied that question for retatrutide specifically. What the evidence does cover is three things that can each look like "it stopped working":
Weight loss slows by design. The steepest drop comes early on every drug in this class, then the curve bends.
Your appetite fights back. Losing weight raises hunger, and the drug's felt effect on appetite fades faster than its effect on what you eat.
The product can differ from vial to vial. Published testing data on research-use peptides shows wide spreads in how much is actually in the vial.
Readers say all three. In BHN's October reader survey (38 readers who chose to answer, not a study), one said their appetite picked up the longer they took it. Another said reta from three different labs gave three different results and side effects. A third said it made them hungrier.
Does reta plateau in the trials?
Not within the trials reported so far, but it slows. In the 48-week phase 2 trial, the 12 mg group lost 17.5% of body weight by week 24 and 24.2% by week 48 (NEJM, 2023). That's about 17 points in the first six months and about 7 in the next six.
The authors were specific about it: participants "continued to lose weight until treatment was stopped at 48 weeks, and the trajectory of the weight-reduction curves indicated that a plateau had not yet been reached."
The phase 3 numbers ran longer:
Trial | Who | What the trial reported |
|---|---|---|
Phase 2 | 338 adults with obesity | 12 mg: -17.5% at 24 weeks, -24.2% at 48 weeks. "A plateau had not yet been reached" |
TRIUMPH-1 | 2,339 adults with obesity | 12 mg: -25.0% at 80 weeks counting everyone, -28.3% counting people who stayed on the drug |
TRIUMPH-1 extension | 532 people with BMI 35+ who finished 80 weeks and tolerated their dose | Up to -30.3% at 104 weeks; Lilly said they "continued to lose weight" |
TRANSCEND-T2D-1 | Adults with type 2 diabetes | Lilly: "weight loss not yet plateauing at 40 weeks" |
Two caveats. The extension group was hand-picked: people who finished and tolerated the drug, given a blinded step-up to their maximum tolerated dose. And these are averages. The phase 2 paper notes "individual variability," and an average curve can still be going down while yours is flat.
When does weight loss slow down on GLP-1 drugs?
Usually somewhere in the second year, and then it holds. Semaglutide has the longest data. In the SELECT trial, about 17,600 adults with heart disease and no diabetes, "weight loss continued over 65 weeks and was sustained for up to 4 years," ending at -10.2% vs -1.5% on placebo at 208 weeks (Nat Med, 2024).
Staying on the drug doesn't mean the scale only moves one way. A post hoc look at three years of Lilly's SURMOUNT-1 tirzepatide trial, in people with prediabetes who took at least 75% of their doses, found the average person regained about 4 kg from their lowest weight by week 176. 70% fell in the paper's "less than 5% regain" group and 8% in its "10% or more" group (Obes Pillars, Sept 2026).
So a stall after a big drop is the normal shape of the curve, not proof the drug quit. Retatrutide's curve just hasn't been followed long enough to show where it flattens.
Why is my appetite coming back on reta?
The best evidence says two things happen, and neither requires the drug to stop working.
The body pushes back. A 2016 analysis estimated that people eat about 100 extra calories a day for every kilogram they lose, more than three times the slowdown in calories burned (Obesity, 2016). That was measured in a diabetes drug trial (canagliflozin, which isn't a GLP-1), but it's the clearest number on how hard appetite fights weight loss.
The felt effect fades before the real one. This is the most useful study for this question. A 60-week trial of semaglutide in 120 adults measured appetite and lunch intake at weeks 20, 40 and 60 (AJCN, June 2026):
People on semaglutide ate about 292, 240 and 270 fewer calories at lunch than placebo at weeks 20, 40 and 60.
At week 20, they also reported less hunger and less food preoccupation.
By weeks 40 and 60, "the groups did not differ significantly in appetite outcomes."
In plain terms: they stopped feeling much less hungry than placebo, but kept eating less. The authors' conclusion was that the drug "continues to help participants consume fewer calories ... even though some subjective benefits decline." It's semaglutide, not retatrutide, and Novo Nordisk helped fund it. Nobody has run this study on retatrutide.
There's also an older finding that the stomach-slowing effect of GLP-1 weakens with constant exposure. In nine healthy volunteers on an 8.5-hour GLP-1 drip, it slowed the stomach much less at the second meal than the first (Diabetes, 2011). That's a lab study of hours, not months, so treat it as a clue, not an answer.
Can reta make you hungrier?
Some users say so, and researchers noticed. A study of Reddit posts from 13,589 people reporting retatrutide use (March 2023 to December 2025) found "increased appetite" was the most common complaint, in 17.1% of users with a mapped symptom. "Food craving" was 7.3% (JAMA Netw Open, Oct 1, 2026).
The authors called that "unexpected given mean weight losses of up to 17.5% at 24 weeks" in the trials, and listed possible reasons, including "product or dose variability," stacking other peptides, and misattribution. They called the findings "hypothesis-generating." Self-reports can't prove the drug caused anything.
In BHN's survey, appetite loss was the most-reported effect among the 26 readers whose main compound was reta (16 of 26). One reader said the opposite. Both can be true of different vials, different people, or different months.
Could the vial be the problem?
It can be, and you can't tell by looking. Every number in the trial sections came from Lilly's own drug. A research-use vial is a different product.
What published testing shows:
Across peptides: A preprint by Mendias and Awan analyzed 6,441 samples of 14 peptides, retatrutide among them, sent to the testing service Finnrick. Depending on the standard applied, 41.6% to 71.1% "failed to meet basic quality criteria" (Preprints.org, April 24, 2026). It hasn't been peer reviewed.
Retatrutide specifically: Finnrick's retatrutide page lists 4,709 tests across 406 sellers since December 2024. Of the 200 most recent shown, 144 passed, 54 failed and 2 were incomplete (Finnrick, read Oct 30, 2026). Its pass bar allows the measured amount to be within 35% of the label, so even a passing vial can be a third off what it says.
That's why "three labs, three different results" is a believable report. If one vial has more in it than the last, the next one can feel like the drug stopped working. Storage matters too: how mixed peptides degrade is covered in how long peptides last in the fridge.
In BHN's survey, 20 of 38 readers had a third-party test on their main compound, 9 had only the seller's COA and 9 had none. How to read the paperwork is in how to read a peptide COA, and what each kind of test can and can't tell you is in how to test peptides for purity.
What happens if you stop reta?
For retatrutide, nobody knows yet. Lilly's TRIUMPH-6 trial is built to answer it: about 643 people take retatrutide for 80 weeks, then are randomized to stay on, switch to a different dose, or switch to placebo for 36 weeks. Primary completion is estimated for April 2028 (ClinicalTrials.gov, NCT06859268).
The approved drugs have answered it, and the answer is consistent:
Trial | Before the switch | After switching to placebo | Stayed on the drug |
|---|---|---|---|
SURMOUNT-4 (tirzepatide) | -20.9% over 36 weeks | +14.0% over the next 52 weeks | -5.5% more |
STEP 4 (semaglutide, Wegovy label Study 5) | 20-week run-in on the drug | +6.9% over the next 48 weeks | -7.9% more |
STEP 1 extension (semaglutide) | -17.3% over 68 weeks | Regained two-thirds of it within a year | Not studied (everyone stopped) |
The STEP 1 extension authors concluded the findings "confirm the chronicity of obesity and suggest ongoing treatment is required." The SURMOUNT-4 authors wrote that "withdrawing tirzepatide led to substantial regain of lost weight." If appetite comes roaring back after a break, that's the expected pattern for this drug class, not something unique to you.
What isn't known yet
How long retatrutide's weight curve keeps going before it flattens. No trial has reported past 104 weeks.
Whether the felt appetite effect fades on retatrutide the way it did on semaglutide. Nobody has measured it.
What happens after stopping retatrutide. TRIUMPH-6 reports around 2028.
Whether a dose change helps at a stall. TRIUMPH-6 has a switch-dose arm, but it's a maintenance trial and has no results. No published trial answers this, and I'm not going to guess.
Anything about a vial that didn't come from Lilly.
The short version
In the trials, retatrutide's weight loss slowed after the first six months but hadn't plateaued at 48 weeks, and kept going to 104 weeks in one group.
On semaglutide and tirzepatide, the curve flattens in the second year, and small regains on treatment are common.
Appetite pushes back as weight comes off, and the "not hungry" feeling can fade while intake stays lower.
Research-use vials vary. Published testing finds wide spreads in purity and amount.
Stopping a drug in this class brings back much of the weight within a year in every withdrawal trial so far.
For every side effect the trials reported, see is retatrutide safe. If you came to reta from tirzepatide, switching from tirzepatide to retatrutide covers what was and wasn't studied.
Has reta stalled for you, or has your appetite come back? Reply and tell me when it happened, whether anything else changed around then (new vial, new seller, a break), and what you noticed. Nobody has studied this in research-use product. You're the dataset.
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