Ranked purely on weight reduction, the order is retatrutide, then tirzepatide, then semaglutide, and each step up adds a receptor. Ranked on evidence, the order reverses completely. Semaglutide is the only one of the three with a cardiovascular outcome trial behind it, and retatrutide, the compound with the biggest number, has never been tested past phase 2.
That inversion is the whole decision. The compound with the most impressive result has the least evidence that the result matters.
One receptor, two, three
Each compound adds a receptor to the one before it, and the additions are not decoration.
Semaglutide belongs to the glucagon-like peptide-1 receptor agonist class.[1] One receptor.
Tirzepatide is a dual agonist at the GIP and GLP-1 receptors, characterised by Thomas and colleagues in work on beta-cell function and insulin sensitivity.[2] Two.
Retatrutide is a triple hormone receptor agonist, adding the glucagon receptor to those two.[3] Three.
The third receptor is the interesting one, and it works differently from the other two. GLP-1 and GIP agonism act largely on appetite and insulin. Glucagon receptor agonism acts on the other side of the ledger: in a randomized study, combined GLP-1 and glucagon receptor agonism was associated with less of the drop in energy expenditure that normally accompanies weight loss.[4]
That is the metabolic adaptation problem, and it is the reason most weight loss stalls. Every dieter who has plateaued has met it. A drug that blunts it is doing something the other two are not.
Head to head on weight reduction
The three headline trials, each in adults with obesity or overweight:
Semaglutide 2.4 mg weekly: mean body weight fell about 15 percent at week 68, against about 2.4 percent on placebo, in the trial reported by Wilding and colleagues.[5]
Tirzepatide: mean body weight fell about 21 percent at the highest dose at week 72, reported by Jastreboff and colleagues.[6]
Retatrutide: mean body weight fell about 24 percent at the highest dose at week 48, in a phase 2 trial.[3]
Mean weight reduction in each compound's pivotal trial
Semaglutide 2.4 mg, 68 weeks: 15
Tirzepatide, 72 weeks: 21
Retatrutide, 48 weeks: 24
Different trials, different durations, different populations. Not a head-to-head comparison.
Read that chart with suspicion. Three separate trials, three durations, three enrolled populations. Cross-trial comparison is the weakest form of evidence there is, and retatrutide’s 24 percent came in the shortest study of the three, before its curve had flattened.
The only randomized direct comparison is narrower than people assume. Frías and colleagues compared once-weekly tirzepatide against semaglutide and found greater weight reduction with tirzepatide, but the population was people with type 2 diabetes rather than obesity without it.[7] That is the sum total of head-to-head randomized evidence among these three. No trial has ever compared retatrutide against either of the others.
Head to head on safety
The adverse event profile is a class property more than a compound property.
Gastrointestinal effects dominate. In the tolerability analysis of once-weekly semaglutide 2.4 mg, nausea, vomiting and diarrhoea were the common events, mostly mild to moderate and transient.[8] The same pattern appears in the tirzepatide and retatrutide trials, and it scales with dose.
Heart rate rises across the class. A meta-analysis measured the effect of these drugs on heart rate in non-diabetic individuals and found an increase.[9] For retatrutide the question is sharper, because glucagon receptor agonism has its own cardiovascular signature and the phase 2 data set is small.
The honest safety statement is uncomfortable: the compound with the most receptors has the fewest patient-years behind it. Semaglutide’s profile is characterised across tens of thousands of participants and several completed outcome trials. Retatrutide’s is characterised across one phase 2 study.
The question nobody wants asked: what happens when you stop
This is where all three converge, and it is the most useful published finding for anyone deciding.
In the extension of the semaglutide weight-management trial, participants regained most of the lost weight within a year of withdrawal, and the cardiometabolic improvements reverted with it.[10]
most of the lost weight regained within a year of stopping semaglutide PMID 35441470
Nothing about that result is specific to semaglutide. It is what happens when you remove a drug that works by suppressing appetite and then stop suppressing appetite. Anyone comparing peak weight reduction across these three compounds is comparing numbers that only hold while the drug is being taken.
The comparison that separates them
Weight reduction is a surrogate. The question underneath it is whether losing the weight this way changes outcomes, and exactly one of these three has an answer.
Lincoff and colleagues ran a cardiovascular outcome trial in adults with overweight or obesity and established cardiovascular disease but without diabetes, and once-weekly semaglutide reduced major adverse cardiovascular events against placebo.[11]
That trial is worth more than the entire weight-reduction comparison above. It is a hard endpoint, in a defined population, showing that the intervention changed something people care about independently of the number on a scale. Tirzepatide’s outcome programme is still reporting. Retatrutide has no cardiovascular outcome data at all, and cannot have any for years.
Choose by what you are optimising for
If you want the evidence, semaglutide. It is the only one of the three with a completed cardiovascular outcome trial, the largest safety database, and published data on what happens after withdrawal.
If you want the effect size with real trial support, tirzepatide. More weight reduction than semaglutide in the one randomized comparison that exists, a completed obesity trial programme, and an outcome programme still in progress.
If you want retatrutide, understand what you are buying. A phase 2 result of about 24 percent at 48 weeks, no phase 3 readout, no outcome data, no comparison against either alternative, and a mechanism whose third receptor is the least characterised of the three. The number is real. The evidence behind the number is a single trial.
Bottom line: the ranking by measured weight reduction runs opposite to the ranking by evidence, and both rankings are correct. Retatrutide produced the largest number in the smallest body of work. Semaglutide produced the smallest number and the only proof that the number translates into anything. Anyone quoting retatrutide’s 24 percent as though it settles the comparison is quoting a phase 2 result against two completed programmes.
This article is for research and informational purposes only and is not intended to diagnose, treat, cure, or prevent any disease. The peptides discussed here are sold for research use only and are not for human consumption. Nothing in this article constitutes medical advice. Consult a qualified clinician before making changes to a health, training, or supplementation protocol.
References
Efficacy and Safety of Glucagon-Like Peptide-1 Receptor Agonists for Weight Loss Among Adults Without Diabetes : A Systematic Review of Randomized Controlled Trials.. Annals of internal medicine, 2025.
Dual GIP and GLP-1 Receptor Agonist Tirzepatide Improves Beta-cell Function and Insulin Sensitivity in Type 2 Diabetes.. The Journal of clinical endocrinology and metabolism, 2021.
Triple-Hormone-Receptor Agonist Retatrutide for Obesity - A Phase 2 Trial.. The New England journal of medicine, 2023.
Glucagon-like peptide-1/glucagon receptor agonism associates with reduced metabolic adaptation and higher fat oxidation: A randomized trial.. Obesity (Silver Spring, Md.), 2023.
Once-Weekly Semaglutide in Adults with Overweight or Obesity.. The New England journal of medicine, 2021.
Tirzepatide Once Weekly for the Treatment of Obesity.. The New England journal of medicine, 2022.
Tirzepatide versus Semaglutide Once Weekly in Patients with Type 2 Diabetes.. The New England journal of medicine, 2021.
Gastrointestinal tolerability of once-weekly semaglutide 2.4 mg in adults with overweight or obesity, and the relationship between gastrointestinal adverse events and weight loss.. Diabetes, obesity & metabolism, 2022.
Effect of glucagon-like peptide-1 receptor agonists on heart rate in non-diabetic individuals with overweight or obesity: a systematic review and pairwise and network meta-analysis of randomized controlled trials.. European journal of medical research, 2026.
Weight regain and cardiometabolic effects after withdrawal of semaglutide: The STEP 1 trial extension.. Diabetes, obesity & metabolism, 2022.
Semaglutide and Cardiovascular Outcomes in Obesity without Diabetes.. The New England journal of medicine, 2023.
