The weight loss drug space moved fast over the last five years. Semaglutide came out and people lost 15% of their body weight. Then tirzepatide pushed that to around 20%. Now retatrutide is showing numbers that make both of those look modest.
So why is retatrutide the best option we have seen so far? The short answer is that it hits three hormone receptors instead of one or two, and the weight loss data from phase 2 trials is unlike anything published before it. working with a coach
Here is what the research actually shows.
What Makes Retatrutide Different From Other Weight Loss Drugs?
Most GLP-1 drugs work by mimicking one hormone. Semaglutide targets GLP-1 receptors. Tirzepatide targets GLP-1 and GIP receptors. Retatrutide targets three receptors, GLP-1, GIP, and glucagon.
That third receptor is the key difference. Glucagon receptor activation increases energy expenditure. Your body burns more calories at rest. The other drugs slow your appetite. Retatrutide slows your appetite and speeds up your metabolism at the same time.
In my experience looking at the mechanistic data, that dual action on intake and expenditure is what separates it. Most obesity drugs only pull one lever. Retatrutide pulls both.
The technical term for this class is triple agonist or GLP-1/GIP/glucagon receptor agonist. It was developed by Eli Lilly, the same company behind tirzepatide.
How Much Weight Can You Lose With Retatrutide?
The phase 2 trial published in the New England Journal of Medicine in 2023 showed participants lost an average of 24.2% of their body weight over 48 weeks at the highest dose tested (12mg). Some participants lost close to 30%.
To put that in real numbers, a person weighing 100kg could expect to lose around 24kg in under a year.
Compare that to the best published results from other drugs. Semaglutide at 2.4mg produced around 14.9% weight loss in the STEP 1 trial. tirzepatide. Retatrutide at 12mg produced 24.2% in its phase 2 trial.
What I found interesting in the data was that weight loss had not plateaued at 48 weeks. The curve was still going down. That suggests the final number in longer trials could be higher.
Is Retatrutide Approved by the FDA?
No. As of 2025, retatrutide is not FDA approved. It completed phase 2 trials with strong results and is currently in phase 3 trials. Phase 3 trials are larger, longer, and required before any drug can be submitted for approval.
If phase 3 results hold up, an FDA submission could happen in 2026 or 2027. Approval would follow after review, which typically takes 6 to 12 months.
This means retatrutide is not available as a prescription drug yet in the US, Australia, or most other countries. Anyone claiming to sell approved retatrutide right now is not selling an approved product.
The phase 3 program is called TRIUMPH and includes multiple trials across different populations including people with type 2 diabetes and cardiovascular disease.
How Does Retatrutide Compare to Semaglutide?
Semaglutide is the active ingredient in Ozempic and Wegovy. It is a single GLP-1 receptor agonist. It works well. The STEP trials showed consistent 15% weight loss and meaningful reductions in cardiovascular events.
Retatrutide produces roughly 60% more weight loss than semaglutide based on the available trial data. It also has a faster onset. Participants in the retatrutide phase 2 trial lost more weight in the first 24 weeks than semaglutide participants lost in 68 weeks.
The side effect profiles are similar. Both cause nausea, vomiting, and gastrointestinal discomfort, especially early in treatment. Retatrutide showed slightly higher rates of nausea at higher doses, which is expected when you add glucagon receptor activity.
One area where semaglutide has a clear advantage right now is availability and evidence base. Semaglutide has years of real-world data, long-term cardiovascular outcome trials, and is available in most countries. Retatrutide has better phase 2 numbers but no approved status and no long-term outcome data yet.
What Conditions Can Retatrutide Treat Beyond Obesity?
The phase 2 trial included people with type 2 diabetes and showed strong reductions in HbA1c, a key marker of blood sugar control. Participants with diabetes lost similar amounts of weight to those without it.
The glucagon receptor component adds something the other drugs do not have. Glucagon plays a role in liver fat metabolism. Early data suggests retatrutide may reduce liver fat more aggressively than GLP-1 only drugs, which makes it a candidate for treating metabolic-associated steatotic liver disease, previously called non-alcoholic fatty liver disease.
Eli Lilly is also running trials for retatrutide in obstructive sleep apnea, heart failure with preserved ejection fraction, and chronic kidney disease. These are the same conditions where semaglutide and tirzepatide have shown benefit, and the expectation is that greater weight loss will produce greater improvements in these conditions.
When I looked at the cardiovascular risk factor data from the phase 2 trial, blood pressure, triglycerides, and waist circumference all improved significantly. These are independent risk factors for heart disease, not just downstream effects of weight loss.
What Are the Side Effects of Retatrutide?
The most common side effects reported in the phase 2 trial were nausea, vomiting, diarrhea, and constipation. These are the same side effects seen with semaglutide and tirzepatide.
Around 20 to 25% of participants at the highest dose reported nausea. Most cases were mild to moderate and occurred during dose escalation. The standard approach with all GLP-1 drugs is to start low and increase the dose slowly over several months to reduce this.
Injection site reactions were reported but uncommon. Heart rate increased slightly at higher doses, which is a known effect of glucagon receptor activation. This is something to monitor in people with existing heart conditions.
Serious adverse events were low and comparable to other drugs in this class. No new safety signals emerged that were not already known from GLP-1 and glucagon receptor research.
One thing worth noting is that muscle loss is a concern with all rapid weight loss interventions. The phase 2 trial did not measure lean mass in detail. This is an open question that phase 3 trials need to address. In my view, anyone using drugs in this class should be doing resistance training and eating adequate protein to protect muscle tissue.
Why the Triple Receptor Approach Changes the Equation
Here is a way to think about it. GLP-1 agonists reduce how much you eat. That is one variable. Adding GIP improves insulin sensitivity and may enhance the GLP-1 effect. That is two variables. Adding glucagon increases how much energy your body burns at rest. That is three variables.
Most obesity interventions only change one variable. Diet changes intake. Exercise changes expenditure. These drugs are now changing both at the same time through a single injection once a week.
What I saw in the phase 2 data was that the dose-response curve was steep. Going from 4mg to 8mg to 12mg produced meaningfully more weight loss at each step. That suggests the glucagon component is adding real metabolic effect, not just a marginal one.
This is a left-of-center way to look at it, but the glucagon receptor activation may actually be the most important part of the retatrutide story. Everyone focuses on GLP-1 because that is where the drug class started. But the energy expenditure side of the equation is where retatrutide separates itself, and that has been the missing piece in obesity pharmacology for decades.
Frequently Asked Questions
When will retatrutide be available?
Phase 3 trials are ongoing as of 2025. If results are strong, an FDA submission could happen in 2026 with potential approval in 2027. Availability in other countries like Australia would follow after local regulatory review.
Is retatrutide better than tirzepatide?
Based on phase 2 data, yes. Retatrutide produced 24.2% weight loss versus 20.9% for tirzepatide at comparable doses. However, tirzepatide has completed phase 3 trials, has FDA approval, and has real-world data. Retatrutide has better numbers on paper but less evidence overall right now. For a comprehensive comparison of all available options, see our guide to the strongest weight loss drug.
Can you get retatrutide now?
Not through approved channels. It is not approved by the FDA, TGA in Australia, or most other regulatory bodies. Clinical trials are ongoing and some people may access it through trial participation.
Does retatrutide work without diet and exercise?
The phase 2 trial included lifestyle counseling for all participants. The drug produces significant weight loss, but combining it with structured nutrition and resistance training produces better body composition outcomes. The drug reduces appetite and increases energy expenditure. Exercise and protein intake protect muscle mass during the weight loss process.
What dose of retatrutide is most effective?
The 12mg dose produced the highest weight loss in phase 2 trials at 24.2% over 48 weeks. Lower doses of 4mg and 8mg produced 8.7% and 17.3% respectively. Higher doses also had higher rates of nausea, which is why dose escalation protocols start low.
The Bottom Line
Why is retatrutide the best weight loss drug in development right now? Because it hits three receptors, reduces appetite, improves insulin sensitivity, and increases energy expenditure simultaneously. The phase 2 weight loss numbers are the highest ever published for a pharmacological intervention in obesity.
It is not approved yet. That matters. The phase 3 data will determine whether those numbers hold in larger, more diverse populations over longer time periods. But based on what we have, the mechanism is sound and the early results are strong.
If you are working on your body composition right now and cannot wait for retatrutide approval, the most effective approach is structured resistance training, high protein intake, and working with a coach who understands how to build a program around your specific situation. The drugs accelerate the process. The fundamentals determine what you keep.