Retatrutide: Weight Loss Approaching 30%. Why Can’t We Use It Yet?
Retatrutide has become one of the most widely discussed investigational drugs for obesity treatment. And there is a reason for that: the results of clinical trials have been remarkable.
In Phase 3 trials, participants receiving the highest doses experienced average weight reductions approaching 30% of their initial body weight—a magnitude that, until recently, was difficult to imagine with pharmacological treatment.
But an increasingly common question is emerging in medical consultations:
If retatrutide works so well, why can’t we use it yet?
The answer involves science, safety, regulatory approval, and a growing problem: the online sale of unapproved products.
What Is Retatrutide?
To understand why this molecule has generated so much interest, it is useful to compare it with medications we already know.
Semaglutide acts primarily on the GLP-1 receptor.
Tirzepatide acts on two receptors:
GIP + GLP-1.
Retatrutide adds a third mechanism. It is a molecule that activates three receptors:
GLP-1 + GIP + glucagon.
For this reason, it is often referred to as a triple agonist. Its manufacturer describes retatrutide as an investigational, once-weekly triple hormone receptor agonist.
GLP-1 and GIP are involved in mechanisms related to satiety, food intake, and metabolic regulation. Activation of the glucagon receptor adds a particularly interesting component to retatrutide’s pharmacological profile and may contribute to its effects on energy balance.
What Have the Studies Found?
The results are substantial.
In the Phase 3 TRIUMPH-4 trial, involving people with obesity or overweight and knee osteoarthritis, without diabetes, the 12 mg dose was associated with an average 28.7% reduction in body weight over 68 weeks. In addition to weight loss, participants experienced improvements in osteoarthritis-related pain and physical function.
The subsequent TRIUMPH-1 trial also reported significant results. At the 12 mg dose, average weight loss reached 28.3% at 80 weeks. Among participants with a baseline BMI of at least 35 kg/m² who continued into a trial extension, average weight loss reached 30.3% at 104 weeks.
However, this does not mean that everyone who may eventually receive retatrutide will lose 30% of their body weight.
These figures represent average results obtained in selected clinical trial populations, under specific inclusion and exclusion criteria, dosing protocols, and structured medical monitoring.
People with diabetes may also respond differently. In the TRIUMPH-2 results released in July 2026, participants with obesity or overweight and type 2 diabetes who received 12 mg experienced an average 20.8% reduction in body weight over 80 weeks.
Why Can’t We Prescribe Retatrutide Yet?
This is the central issue.
Retatrutide remains an investigational medication.
As of September 2026, it is not approved for routine clinical use, and its efficacy and safety continue to be evaluated through the clinical development program. Lilly has indicated that it plans to submit regulatory documentation to the US Food and Drug Administration (FDA) in 2027.
Therefore, extraordinary clinical trial results do not mean that a medication has been approved.
Before a new drug becomes available to the public, regulatory authorities must evaluate the complete body of evidence concerning efficacy, safety, adverse events, manufacturing quality, dosing, indications, and the overall benefit–risk balance.
A New Conflict Between Physicians and Patients
This situation has created a dilemma that is becoming increasingly relevant in clinical practice.
A patient reads about weight loss approaching 30% and thinks:
“If it works so well, why do I have to wait?”
The physician must ask a different question:
“How can I prescribe a medication that has not yet been approved, especially when I cannot even guarantee the origin of products purchased outside clinical trials?”
This is not about opposing innovation. Quite the opposite: retatrutide may represent an important advance in obesity treatment.
However, scientific enthusiasm and clinical availability are two different things.
The Dangers of Buying “Retatrutide” Online
This may be one of the most concerning aspects of the current situation.
Products advertised as retatrutide are being sold through unregulated channels even though the molecule remains investigational.
In this context, discussing whether retatrutide is effective is not enough. We must ask:
What is actually inside that vial?
Without a regulated pharmaceutical supply chain, serious uncertainties arise regarding purity, concentration, sterility, contamination, storage conditions, and dosage.
And the problem is no longer merely theoretical.
In September 2026, Australian authorities warned about a counterfeit product sold as retatrutide that, upon analysis, was found to contain semaglutide at a concentration substantially higher than that found in approved medications. The case was associated with severe vomiting and esophageal injury.
This episode illustrates why purchasing a product labeled “retatrutide” does not necessarily mean receiving retatrutide.
Is Retatrutide the Future of Obesity Treatment?
It may become one of the molecules that shape that future.
The results available so far suggest that obesity pharmacotherapy is entering a new phase. Drug development is moving beyond targeting a single hormonal pathway toward molecules capable of simultaneously modulating different mechanisms involved in appetite and metabolism.
However, we must avoid two extremes.
The first is dismissing an innovation simply because it is still under development.
The second—and potentially more dangerous—is interpreting promising scientific findings as permission to use experimental products before their quality and safety have been adequately established.
Good medical practice must navigate between these two extremes.
What Would I Tell My Patient Today?
Retatrutide is an extremely promising molecule, and the clinical trial results justify scientific enthusiasm.
However, at this stage, I do not consider it appropriate to use products marketed through unregulated channels as retatrutide.
For people who need obesity treatment today, approved medications and other therapeutic strategies are already available and can be evaluated individually by a physician.
Once retatrutide completes its clinical development and undergoes regulatory evaluation, we will be able to discuss a question that is much more important than simply:
“How much weight does it help people lose?”
We will be able to ask:
“For which patient is it the most appropriate option, and what are its benefits, risks, and therapeutic goals?”
That is the question that truly matters in medicine.
Dr. Andrea Pereira, MD, PhD Physician Specialized in Clinical Nutrition
References:
Retatrutide: Pitting Physician Against Patient. Medscape. 2026.
Giblin K, Kaplan LM, Somers VK, et al. Retatrutide for the treatment of obesity, obstructive sleep apnea and knee osteoarthritis: rationale and design of the TRIUMPH registrational clinical trials. Diabetes Obes Metab. 2026;28(1):83–93.
Eli Lilly and Company. Lilly's triple agonist retatrutide delivered weight loss averaging 28.7% in first Phase 3 trial. 11 dez. 2025.
Eli Lilly and Company. Lilly's triple agonist retatrutide delivered powerful weight loss in Phase 3 trial. 21 maio 2026.
Eli Lilly and Company. What to know about retatrutide. 2026.
Medical disclaimer: This article is intended for educational and informational purposes only. It does not replace an individual medical consultation, diagnosis, or prescription.
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