Marina, 34 years old, comes in for an appointment with a direct question: she saw in a WhatsApp group an offer for a weight loss pen called retatrutide, advertised as "stronger than the others" and "without side effects". She wants to know if she can trust it.

  • "The data and clinical case cited in this article are fictional and have a purely illustrative purpose, serving to facilitate understanding of the topic addressed."*

This question has become even more current because the National Health Surveillance Agency (Anvisa) published an official alert on the subject this Friday, July 24th. It's worth carefully understanding what is already scientifically known about this substance, and why the answer for Marina needs to be careful.

What is retatrutide?

Retatrutide is a molecule still in the phase of clinical research, developed for the treatment of obesity and type 2 diabetes. It acts on three hormones linked to metabolism (GLP-1, GIP, and glucagon), which sets it apart from medications already approved on the market, which usually act on one or two of these targets.

Why is it not yet approved for use?

According to Anvisa, the pharmaceutical company responsible for its development has not yet requested health registration in Brazil or in any other country. This means that the substance remains in an advanced phase of studies, but the complete set of research that proves its benefit, safety, and quality has not yet been completed. There is, at the moment, no official prediction of when it will reach the market.

Even so, products advertised as retatrutide are already circulating in the underground market, often with professional-looking packaging, which guarantees nothing about the actual origin or composition of the contents.

What do the studies already show about side effects?

In official and controlled clinical trials, the most common adverse effects are gastrointestinal, such as nausea, diarrhea, constipation, and vomiting, following the same pattern observed in other medications in the same class. At the highest doses tested, these symptoms appear in a relevant portion of participants, usually mild to moderate in intensity and concentrated at the beginning of treatment.

A finding that caught the researchers' attention was dysesthesia, an unusual alteration in skin sensation, reported by some participants who used the highest dose, something that had not been described in similar medications already approved. A slight temporary increase in heart rate was also observed in some people.

So far, in published studies, the rate of events considered severe was similar between those who used the medication and those who used placebo, and no concerning signs related to the heart were identified. But it is important to understand what this really means.

Why "we still don't know" weighs so heavily here

Even with promising results, the studies so far have involved a significantly smaller number of participants than necessary to detect rare and serious effects, which only appear when thousands of people use the medication for several years. Also missing is the most important outcome for a long-term use treatment: the study dedicated to evaluating long-term cardiovascular safety, which is still ongoing.

In other words, even in the studied version, with the correct dose, guaranteed source, and medical follow-up, there are still open questions about what happens after years of use. This is exactly why the approval of a medication depends on gathering a robust volume of data before it reaches the shelves.

And the product sold illegally, is it the same thing?

No. And that is perhaps the most important information in this text. When someone buys an unregistered version, outside the official research circuit, they lose any guarantee about:

  • Whether the substance inside the pen is actually retatrutide
  • What the actual concentration of the product is
  • How it was stored and transported
  • Whether the applied dose corresponds to what is stated on the packaging

This means that, in addition to the already-known risk of adverse effects studied in clinical trials, a second risk is added, one that is completely preventable: that of using a substance of unknown origin and composition, with no quality control behind it.

What's worth taking away from this story

For patients like Marina, medical guidance does not change with the hype on social media: medications without health registration should not be purchased or used, under no circumstances. This is not about distrusting the science behind retatrutide, which continues its normal path of research, but rather about understanding that we are still in the middle of that path, not at the end of it.

This content is for informational and educational purposes and does not replace individualized medical consultation. Each organism responds differently to treatments, and decisions about medication use should always be made with a trusted physician.

Dr. Rebeca Soares Andrade CRM - GO 39335