Marina, 34 years old, arrives for a consultation with a straightforward question: she saw in a WhatsApp group an offer for a weight-loss pen called retatrutide, advertised as "stronger than the others" and "with no side effects". She wants to know if she can trust it.

  • "The data and clinical case cited in this article are fictitious and are intended purely for illustrative purposes, to facilitate understanding of the topic addressed."*

This question has become even more timely because the National Health Surveillance Agency (Anvisa) published an official alert on the subject this Friday, 24 July. It is worth understanding carefully 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 clinical research phase, developed for the treatment of obesity and type 2 diabetes. It acts on three hormones linked to metabolism (GLP-1, GIP and glucagon), which distinguishes it 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 regulatory registration in Brazil or in any other country. This means that the substance is still in an advanced phase of studies, but the complete set of research proving its benefits, safety and quality has not yet been completed. There is, at present, no official forecast of when it will reach the market.

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

What do studies already show about side effects?

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

A finding that caught the attention of researchers was dysaesthesia, an uncommon alteration in skin sensitivity, reported by some of the 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 serious 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 much 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 treatment intended for prolonged use: the study dedicated to assessing long-term cardiovascular safety, which is still ongoing.

In other words, even in the studied version, with the correct dose, guaranteed source and medical supervision, there are still open questions about what happens after years of use. This is precisely 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 this 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 really retatrutide
  • What the actual concentration of the product is
  • How it was stored and transported
  • Whether the dose applied corresponds to that stated on the packaging

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

What is worth taking from this story

For patients like Marina, medical guidance does not change with the hype on social media: medications without regulatory registration should not be purchased or used, under any circumstances. This is not about distrusting the science behind retatrutide, which continues on its normal research path, but rather about understanding that we are still in the middle of that path, not at the end of it.

This content is informative and educational in nature and does not replace individualised medical consultation. Each organism responds differently to treatments, and decisions about medication use should always be made together with a trusted physician.

Dr. Rebeca Soares Andrade CRM - GO 39335