TLDR
Retatrutide, tirzepatide, and semaglutide act on different combinations of metabolic hormone receptors.
Semaglutide: GLP-1 receptor agonist.
Tirzepatide: GIP + GLP-1 receptor agonist.
Retatrutide: GIP + GLP-1 + glucagon receptor agonist.
In separate obesity trials without diabetes, semaglutide produced about 14.9% average weight loss at 68 weeks in STEP 1, tirzepatide produced up to 20.9% at 72 weeks in SURMOUNT-1, and peer-reviewed Phase 2 retatrutide produced 24.2% at 48 weeks. Lilly has since reported a 28.3% Phase 3 retatrutide efficacy-estimand result at 80 weeks.
Those numbers cannot be used as a valid head-to-head ranking because they came from different trials involving different participants, durations, statistical estimands, dose schedules, and study protocols.
We do have a direct randomized comparison between tirzepatide and semaglutide. In SURMOUNT-5, tirzepatide produced 20.2% average weight reduction versus 13.7% with semaglutide after 72 weeks.
We do not yet have completed head-to-head retatrutide-versus-tirzepatide results. TRIUMPH-5 is designed specifically to answer that question, but as of September 2026 ClinicalTrials.gov lists it as active and not recruiting, with completion expected in December 2026.
So the research currently supports saying that retatrutide has produced exceptionally large weight reductions in its own trials. It does not yet support saying that a randomized clinical trial has proven retatrutide superior to tirzepatide.
Three Peptide Drugs, Three Different Receptor Strategies
Semaglutide, tirzepatide, and retatrutide are often discussed as successive generations of the same idea.
There is some truth to that.
But describing them simply as “GLP-1, GLP-2, and GLP-3 drugs” is scientifically wrong.
Their receptor pharmacology is:
| Molecule | GLP-1R | GIPR | GCGR | Current Status |
|---|---|---|---|---|
| Semaglutide | Yes | No | No | FDA-approved products |
| Tirzepatide | Yes | Yes | No | FDA-approved products |
| Retatrutide | Yes | Yes | Yes | Investigational |
There is no GLP-2 or GLP-3 receptor progression involved here.
Tirzepatide does not activate “two GLP receptors.”
Retatrutide does not activate “three GLP receptors.”
The additional receptors are GIPR and GCGR.
Semaglutide Established the Modern GLP-1 Obesity Benchmark
Semaglutide is a long-acting GLP-1 receptor agonist.
In the STEP 1 trial, 1,961 adults with obesity or overweight without diabetes were randomized to once-weekly semaglutide 2.4 mg or placebo for 68 weeks.
Mean body-weight change was:
-14.9% with semaglutide
versus
-2.4% with placebo.
About 86% of semaglutide participants with available week-68 data lost at least 5%, roughly 69% lost at least 10%, and approximately half lost at least 15%.
This was a major change in obesity pharmacotherapy because average weight reduction approached ranges that had previously been difficult to achieve pharmacologically.
Tirzepatide Added GIP Receptor Activity
Tirzepatide activates both GIP and GLP-1 receptors.
SURMOUNT-1 tested tirzepatide in 2,539 adults with obesity or overweight without diabetes for 72 weeks.
At the highest 15 mg dose, mean weight reduction was approximately 20.9%.
That was substantially larger than the average weight reduction seen in STEP 1 with semaglutide, although these were separate trials and therefore not a direct comparison.
The obvious next question was whether tirzepatide would actually outperform semaglutide when both were tested in the same randomized trial.
Eventually, that experiment was performed.
SURMOUNT-5 Directly Compared Tirzepatide With Semaglutide
SURMOUNT-5 is important because it avoids the major weakness of comparing unrelated trial percentages.
The Phase 3b trial randomized 751 adults with obesity and no type 2 diabetes to receive the maximum tolerated dose of either:
tirzepatide 10 or 15 mg,
or semaglutide 1.7 or 2.4 mg.
Treatment lasted 72 weeks.
Mean weight reduction was:
20.2% with tirzepatide
and
13.7% with semaglutide.
Mean waist reduction was 18.4 cm with tirzepatide and 13.0 cm with semaglutide.
The difference in weight reduction was statistically significant.
This is much stronger evidence for the statement:
tirzepatide produces greater average weight reduction than semaglutide in this population
than comparing SURMOUNT-1 against STEP 1.
Where Does Retatrutide Fit?
Retatrutide adds glucagon receptor agonism to GIP and GLP-1 receptor activity.
The original Phase 2 obesity trial reported:
1 mg: -8.7%
4 mg: -17.1%
8 mg: -22.8%
12 mg: -24.2%
at 48 weeks.
The placebo group lost 2.1%.
Even before Phase 3, those results suggested that retatrutide might produce larger average weight reductions than earlier incretin therapies.
But “suggested” is the correct word.
There was no semaglutide arm.
There was no tirzepatide arm.
The study only demonstrated retatrutide’s efficacy relative to placebo.
Phase 3 Retatrutide Has Pushed the Numbers Higher
TRIUMPH-1 subsequently reported an efficacy-estimand average weight reduction at 80 weeks of:
4 mg: 19.0%
9 mg: 25.9%
12 mg: 28.3%
placebo: 2.2%.
That 28.3% figure is larger than the headline averages from STEP 1, SURMOUNT-1, and SURMOUNT-5.
It is therefore tempting to write:
Retatrutide is more effective than tirzepatide and semaglutide.
The evidence is not quite there yet.
Why You Cannot Rank the Drugs Using Three Separate Trials
Imagine three schools give different exams.
School A gives a 68-week test.
School B gives a 72-week test.
School C gives an 80-week test.
The students have different starting characteristics.
The grading rules differ.
Treatment discontinuation is handled differently.
Some studies estimate outcomes regardless of adherence.
Others emphasize outcomes assuming continued treatment.
Simply comparing the final percentages does not isolate the drug effect.
Obesity trials differ in:
duration;
baseline BMI;
percentage of women and men;
diabetes status;
dose escalation;
adherence;
management of missing data;
rescue therapy;
statistical estimands.
That is why randomized head-to-head trials are so valuable.
They place the treatments inside the same experimental framework.
The Statistical Estimand Makes a Big Difference for Retatrutide
This issue is particularly relevant to the 28.3% TRIUMPH-1 number.
Under the study’s efficacy estimand, retatrutide 12 mg produced:
-28.3%.
Under the treatment-regimen estimand, which included the effects of discontinuation and prohibited weight-management treatments:
-25.0%.
Both are legitimate estimates.
But if we compare 28.3% retatrutide with a number from another drug trial that used a more treatment-policy-like approach, we may inadvertently favor one therapy because of statistical design rather than biology.
This is one reason network meta-analyses try to standardize evidence more carefully.
What Do Network Meta-Analyses Say?
A network meta-analysis combines direct and indirect evidence across randomized trials.
It can estimate comparisons between drugs that have not yet been randomized against one another.
A 2024 network meta-analysis of 27 trials and more than 15,000 participants ranked retatrutide 12 mg and 8 mg highest for weight reduction, estimating placebo-adjusted reductions of approximately 22.1% and 20.7%, respectively. Tirzepatide 15 mg followed at approximately 16.5%.
Those results support the possibility that retatrutide may produce greater weight loss.
But network estimates are indirect evidence.
They are only as strong as the comparability of the trials forming the network.
A 2026 BMJ Analysis Was More Cautious
A much larger 2026 BMJ systematic review and network meta-analysis included 262 randomized trials involving nearly 100,000 participants and 19 drugs.
It found moderate-to-high certainty evidence supporting substantial one-year weight reduction with established agents such as tirzepatide and semaglutide.
Emerging drugs including retatrutide appeared capable of producing similarly large or greater effects.
But the certainty for those emerging agents was judged low to very low, reflecting their much smaller and less mature evidence bases at the review’s search cutoff.
This is an important distinction.
Retatrutide can have the largest observed weight-loss number while simultaneously having less mature evidence than an older drug.
Those statements are not contradictory.
TRIUMPH-5 Should Give Us the Comparison We Actually Need
Rather than relying indefinitely on indirect comparisons, Lilly started TRIUMPH-5.
TRIUMPH-5 is a Phase 3 randomized, double-blind study directly comparing:
retatrutide
with
tirzepatide
in adults with obesity.
ClinicalTrials.gov lists approximately 800 planned participants and an estimated primary completion in December 2026. As of September 2026, the study is active but no longer recruiting, and no results are posted.
Until that trial reports, the strongest statement remains:
Retatrutide has produced larger average weight reductions in separate trials, but superiority over tirzepatide has not yet been demonstrated in a completed head-to-head randomized study.
Mechanistically, Is Triple Agonism Necessarily Better Than Dual Agonism?
No.
More receptors do not automatically mean better therapy.
Retatrutide’s glucagon receptor activity was deliberately engineered because preclinical research suggested it could add effects on:
energy expenditure,
substrate metabolism,
and liver metabolism.
But glucagon also promotes hepatic glucose production.
The challenge is therefore balancing GCGR activity against GLP-1 and GIP activity rather than simply maximizing all three receptors.
The final effect depends on relative receptor potency, pharmacokinetics, tissue distribution, dose, and duration.
Retatrutide’s performance is evidence about this specific engineered molecule, not evidence that every triple agonist must outperform every dual agonist.
Weight Loss Is Only One Measure of “Better”
A drug that produces the most weight loss is not automatically the best-supported treatment.
Researchers also need to evaluate:
cardiovascular outcomes;
kidney outcomes;
type 2 diabetes outcomes;
body composition;
quality of life;
long-term tolerability;
treatment discontinuation;
rare adverse effects.
This is where the evidence maturity differs substantially between the drugs.
Semaglutide Has Much More Mature Cardiovascular Outcome Evidence
The SELECT trial enrolled 17,604 adults with overweight or obesity and established cardiovascular disease but no diabetes.
Participants received semaglutide 2.4 mg or placebo.
Over a mean follow-up of approximately 40 months, the primary cardiovascular composite occurred in:
6.5% of semaglutide participants
versus
8.0% of placebo participants.
The hazard ratio was 0.80, representing a 20% relative reduction in the primary composite outcome.
Based on this evidence, FDA approved Wegovy for reducing cardiovascular death, heart attack, and stroke in adults with cardiovascular disease and overweight or obesity.
Retatrutide does not yet have comparable cardiovascular outcome evidence.
Retatrutide’s TRIUMPH-3 Cardiovascular Results Do Not Answer the Outcome Question
TRIUMPH-3 included people with established cardiovascular disease, so cardiovascular events were measured.
But the study was not powered as a definitive cardiovascular-outcomes trial.
Lilly reported a MACE-3 hazard ratio of 1.12 with a 95% confidence interval from 0.64 to 1.96 for pooled retatrutide versus placebo.
That interval is extremely wide.
It is compatible with several very different possibilities.
The correct conclusion is not that retatrutide increases cardiovascular risk.
Nor is it that retatrutide reduces cardiovascular risk.
The trial simply did not provide a precise answer to that question.
A dedicated retatrutide cardiovascular and kidney outcomes program is ongoing.
Safety Comparisons Also Require Direct Evidence
All three molecules commonly cause gastrointestinal adverse effects.
Nausea, diarrhea, constipation, and vomiting occur frequently during dose escalation.
But simply comparing percentages between STEP, SURMOUNT, and TRIUMPH trials is problematic for the same reason that efficacy comparisons are problematic.
The trials used:
different escalation schedules;
different populations;
different durations;
different adverse-event collection periods.
SURMOUNT-5 is more informative because semaglutide and tirzepatide were studied together. It found gastrointestinal adverse events were the most common in both groups and were generally mild to moderate.
For retatrutide, Phase 3 has also identified dysesthesia as an event worth watching.
In TRIUMPH-1, Lilly reported dysesthesia in 5.1%, 12.3%, and 12.5% of participants receiving 4, 9, and 12 mg versus 0.9% with placebo.
TRIUMPH-4 reported 20.9% at 12 mg in that particular population.
Complete peer-reviewed Phase 3 safety publications will help determine how important that signal proves to be.
Diabetes Changes the Comparison
People with type 2 diabetes generally lose less weight in incretin-based obesity trials than people without diabetes.
Retatrutide illustrates this clearly.
TRIUMPH-1 without diabetes reported 28.3% at 12 mg under the efficacy estimand.
TRIUMPH-2 with diabetes reported 20.8% at 12 mg.
The same general pattern has been observed with tirzepatide and semaglutide.
This means it is especially misleading to compare a non-diabetic retatrutide obesity trial with a diabetes trial of another drug.
Population matching matters.
Treatment Duration Matters Too
STEP 1 ran 68 weeks.
SURMOUNT-1 ran 72 weeks.
TRIUMPH-1’s primary analysis occurred at 80 weeks.
The retatrutide Phase 2 study ran 48 weeks.
If a treatment’s weight curve is still falling at the endpoint, a longer study can produce a larger final percentage even if the underlying pharmacology is not dramatically different.
That does not explain all the apparent differences between these drugs.
But it is one more reason raw cross-trial percentages are not equivalent to randomized comparison.
What Can We Say With High Confidence?
We can confidently say that all three drugs produce substantial average weight reduction.
Semaglutide has established GLP-1 receptor agonist efficacy and a large clinical-outcomes evidence base.
Tirzepatide has demonstrated greater average weight reduction than semaglutide in a direct randomized trial.
Retatrutide has produced larger average weight reductions in its own obesity trials than the headline averages reported in major semaglutide and tirzepatide studies.
And retatrutide’s Phase 3 program has reproduced large effects in several populations.
What we cannot yet say with the same confidence is:
Retatrutide has been proven superior to tirzepatide.
That trial is still underway.
Which Drug Has the Strongest Evidence?
That depends on what “strongest” means.
If the question is largest observed average weight reduction in a trial, retatrutide currently has the largest headline numbers of the three.
If the question is direct evidence against semaglutide, tirzepatide has the advantage because SURMOUNT-5 directly compared the two.
If the question is long-term cardiovascular outcome evidence in obesity, semaglutide currently has especially strong evidence through SELECT.
If the question is maturity of the overall safety database, semaglutide and tirzepatide have the advantage because they are approved and have much larger post-approval exposure.
Retatrutide remains the least mature clinically because it is still investigational.
The Most Useful Comparison Today
The research does not support reducing these drugs to:
good, better, best.
A better scientific summary is:
Semaglutide proved that a long-acting GLP-1 receptor agonist could produce large pharmacological weight loss and has mature cardiovascular-outcome evidence.
Tirzepatide showed that adding GIP receptor agonism could produce still greater average weight loss and directly outperformed semaglutide in SURMOUNT-5.
Retatrutide adds glucagon receptor agonism and has produced extremely large weight reductions in Phase 2 and Phase 3 trials, but its direct comparison with tirzepatide and its long-term outcome evidence are still pending.
That is where the evidence stands as of September 2026.
FAQs
Is retatrutide better than tirzepatide?
That has not yet been established in a completed direct randomized trial. Retatrutide has produced larger average weight reductions in separate trials, but TRIUMPH-5 is the trial designed to compare retatrutide directly with tirzepatide.
Has tirzepatide been proven better than semaglutide for weight loss?
Yes, in the SURMOUNT-5 population. At 72 weeks, average weight reduction was 20.2% with tirzepatide versus 13.7% with semaglutide.
Which produced the most weight loss in its own trial?
Retatrutide has produced the largest reported average efficacy-estimand weight reductions among these three, including 28.3% at 80 weeks in TRIUMPH-1.
Does retatrutide work through three GLP receptors?
No. It activates GIP, GLP-1, and glucagon receptors.
Why might glucagon receptor activation increase weight loss?
Preclinical studies suggest glucagon receptor activity can influence energy expenditure and substrate metabolism. The quantitative importance of this mechanism in humans is not yet established.
Which drug has the strongest cardiovascular evidence?
Semaglutide has a large randomized cardiovascular-outcomes trial in people with overweight or obesity without diabetes, and FDA has approved Wegovy for cardiovascular risk reduction in an indicated population. Retatrutide’s definitive cardiovascular-outcome evidence is still being developed.
Is retatrutide approved?
No. It remains investigational as of September 2026.
References
Jastreboff AM, Kaplan LM, Frías JP, et al. Triple-Hormone-Receptor Agonist Retatrutide for Obesity: A Phase 2 Trial. New England Journal of Medicine. 2023. PubMed record
Jastreboff AM, Aronne LJ, Ahmad NN, et al. Tirzepatide Once Weekly for the Treatment of Obesity. New England Journal of Medicine. 2022. SURMOUNT-1 article
Wilding JPH, Batterham RL, Calanna S, et al. Once-Weekly Semaglutide in Adults with Overweight or Obesity. New England Journal of Medicine. 2021. STEP 1 article
Aronne LJ, Horn DB, le Roux CW, et al. Tirzepatide as Compared with Semaglutide for the Treatment of Obesity. New England Journal of Medicine. 2025. SURMOUNT-5 article
Nong K, Shi Q, Xie X, et al. Comparative effects of drugs for adults with overweight or obesity: systematic review and network meta-analysis. BMJ. 2026;394:e372161. BMJ systematic review
Lincoff AM, Brown-Frandsen K, Colhoun HM, et al. Semaglutide and Cardiovascular Outcomes in Obesity without Diabetes. New England Journal of Medicine. 2023. SELECT trial article
U.S. Food and Drug Administration. FDA Approves First Treatment to Reduce Risk of Serious Heart Problems Specifically in Adults with Obesity or Overweight. March 8, 2024. FDA announcement
ClinicalTrials.gov. TRIUMPH-5: Retatrutide Compared with Tirzepatide in Adults With Obesity. NCT06662383. TRIUMPH-5 trial record
Eli Lilly and Company. TRIUMPH-1 Phase 3 results. May 21, 2026. Lilly TRIUMPH-1 results
Eli Lilly and Company. TRIUMPH-2 and TRIUMPH-3 Phase 3 results. July 23, 2026.