Fat Loss
Three drugs get discussed as though they are versions of the same thing. They are not. They hit different receptors, produce meaningfully different results, and only two of them are approved.
Here is what the published trials actually show.
All three work on gut hormone pathways that regulate appetite, satiety and blood sugar. The difference is how many of those pathways each one activates.
Semaglutide is a GLP-1 receptor agonist. One target. It mimics glucagon-like peptide-1, which slows gastric emptying, increases satiety and improves insulin response.
Tirzepatide is a dual agonist, hitting both GIP and GLP-1 receptors. Adding GIP appears to improve both the weight outcome and the metabolic response beyond what GLP-1 alone achieves.
Retatrutide is a triple agonist: GIP, GLP-1 and glucagon. The glucagon component is the interesting one, because glucagon increases energy expenditure rather than only suppressing intake. It is a different lever entirely.
Broadly, more targets has meant more weight loss. That pattern holds across the trial data so far.
These are the headline figures from the pivotal studies. Read them as averages from controlled trials, not as what any individual should expect.
Semaglutide 2.4 mg. The STEP 1 trial ran 68 weeks and reported mean weight loss of around 15 percent, against roughly 2.4 percent on placebo.
Tirzepatide 15 mg. SURMOUNT-1 ran 72 weeks and reported mean weight loss of around 21 percent.
Retatrutide 12 mg. The Phase 3 TRIUMPH-1 trial, reported in May 2026, found mean weight loss of 28.3 percent at 80 weeks, with 45.3 percent of participants losing 30 percent or more of their body weight. In a study extension, participants with a starting BMI of 35 or above reached an average of 30.3 percent at 104 weeks.
That last figure is the reason this drug is being discussed the way it is. Thirty percent average weight loss is territory previously associated with bariatric surgery.
This matters more than the efficacy numbers and gets glossed over constantly.
Semaglutide is approved for weight management, under the Wegovy brand, and for type 2 diabetes as Ozempic.
Tirzepatide is approved, as Zepbound for weight management and Mounjaro for diabetes.
Retatrutide is not approved anywhere. It remains investigational. Eli Lilly has stated it plans to submit a Biologics License Application to the US FDA in the first quarter of 2027, which means approval, if it comes, would follow some time after that. It cannot be legally prescribed as an approved medicine, is not available in pharmacies, and anything sold as retatrutide outside a clinical trial has no regulatory oversight of what is actually in the vial.
There is also now an approved oral option in this class. Orforglipron, sold as Foundayo, was approved by the US FDA in April 2026 as the first daily GLP-1 pill for weight management that can be taken with no food or water restrictions, and an oral form of semaglutide was approved shortly before it. Neither matches the injectables on raw weight loss so far, but a daily tablet changes the practical picture for anyone who cannot or will not inject. Which route fits is a conversation for a doctor rather than a fitness site.
Three things the headline numbers do not tell you, and all three matter more than the difference between 21 and 28 percent.
A trial mean of 21 percent contains people who lost 35 percent and people who lost 5 percent. Response varies substantially and is not well predicted in advance. The average tells you about the drug; it tells you very little about you.
This is the most consistent finding across the entire class and the least discussed. When treatment stops, weight regain is the norm. The STEP 4 withdrawal study showed participants regaining a substantial portion of lost weight after stopping semaglutide.
These are not short courses. They are ongoing treatments for a chronic condition, and the trials are designed around that assumption. Anyone framing these as a temporary fix has misunderstood what the evidence shows.
Rapid weight loss from any cause costs lean tissue alongside fat, and the proportion lost as lean mass in GLP-1 trials has been a recurring concern in the literature.
This is the single most actionable point in the whole article. Adequate protein intake and resistance training during treatment substantially change what you end up with. Two people losing the same 20 kilos can arrive at very different body compositions depending on whether they trained and ate enough protein while it happened.
If you are on one of these, the protein calculator sets a target based on your current bodyweight and activity, and it is worth being deliberate about rather than approximate.
Gastrointestinal effects dominate across all three: nausea, vomiting, diarrhoea, constipation. They are usually worst during dose escalation and settle for most people, though not everyone.
Discontinuation due to adverse effects rises with dose across the class, which is part of why titration is gradual rather than starting at a target dose.
Retatrutide's trial reporting has also included dysesthesia, meaning altered skin sensation, at a notable rate in the higher dose groups. That is a newer signal and one to watch as more Phase 3 data publishes.
None of this is a reason to avoid them. It is a reason to be under medical supervision while taking them.
All of these are prescription medicines. In India they fall under the Drugs and Cosmetics Act, 1940, and lawful use requires a prescription from a registered medical practitioner.
Dosing is also not a fixed thing. Every one of these drugs is titrated upward gradually over weeks, and the schedule depends on how you tolerate each step. Someone struggling with nausea at a low dose needs a different escalation to someone who has no symptoms at all.
What you can usefully understand is how titration works and what the trial schedules looked like. The GLP-1 titration calculator lays out the escalation structure used in the studies, and the GLP-1 weight loss predictor models the trajectory from trial data rather than promising an outcome.
If the decision is live for you, these are the questions that actually matter, and none of them is "which produced the biggest number".
The drug matters less than the plan around it. A person on semaglutide who trains, eats enough protein and has a maintenance strategy will end up in a better place than someone on the most potent compound available with none of that.
In trial averages, tirzepatide produced greater weight loss, around 21 percent at 72 weeks in SURMOUNT-1 against around 15 percent at 68 weeks for semaglutide in STEP 1. Both are approved. Individual response varies and the choice belongs with a prescribing doctor.
No. As of September 2026 it remains investigational. Eli Lilly has stated it plans to submit a Biologics License Application to the FDA in the first quarter of 2027. It cannot be legally prescribed as an approved medicine anywhere.
In the Phase 3 TRIUMPH-1 trial, participants on 12 mg lost an average of 28.3 percent of body weight at 80 weeks, with 45.3 percent losing 30 percent or more. A study extension in participants with BMI 35 or above reached 30.3 percent at 104 weeks. These are trial averages, not individual guarantees.
Generally yes. Weight regain after discontinuation is consistently observed across the class, which is why these are described as ongoing treatments for a chronic condition rather than short courses.
Rapid weight loss from any cause includes lean tissue, and the lean mass component in GLP-1 trials has been a recurring concern. Adequate protein intake and resistance training during treatment meaningfully change the final body composition.
GLP-1 agonists like semaglutide target one receptor. Dual agonists like tirzepatide add GIP. Triple agonists like retatrutide add glucagon, which raises energy expenditure rather than only reducing intake. More targets has generally meant more weight loss in trials so far.
This article is educational and is not medical advice. See the medical disclaimer.
Want a programme built around your own numbers?
Work With Dinesh
Newsletter
One email when a new guide, calculator or breakdown goes live. Nothing else.
