Retatrutide, an experimental weight-loss injection nicknamed the “Godzilla” of slimming drugs, may be associated with a wide range of concerning symptoms, according to new research.
People who said they were taking the drug reported 129 different problems, including burning sensations on the skin, a racing heartbeat, panic attacks and depression.
Often referred to as “reta”, retatrutide remains in clinical trials and has not been approved for use anywhere in the world.
Despite that, people in the UK and elsewhere have reportedly obtained the injection through illegal channels and administered it themselves.
The “Godzilla” comparison comes from trial results suggesting retatrutide could be more potent than Mounjaro, with participants losing as much as a quarter of their body weight in roughly 18 months.
Medical experts warn that taking an unlicensed drug before its safety profile has been fully established carries serious risks. There is also no guarantee that products sold illegally contain retatrutide at all.
For the study, published in JAMA Network Open, researchers reviewed 148,640 Reddit posts discussing retatrutide.
They then identified 13,589 users who claimed to have taken the drug and examined the adverse effects described in their posts.
People claiming to use retatrutide described 129 symptoms, including burning skin, a rapid heartbeat, panic attacks and depression
Researchers at the University of Pennsylvania found that 7,823 of those users had mentioned at least one side effect.
That figure represents more than half of the people who said they were using the injection, while many individuals described experiencing several symptoms.
The reported reactions were grouped into 14 categories, covering problems such as digestive symptoms, mental health changes, heart-related issues and skin conditions.
The most frequently mentioned symptom was unexpectedly increased appetite. It was reported by 1,336 people, or almost one in five of the users studied.
Most weight-loss injections suppress hunger by mimicking GLP-1, a gut hormone released after eating that helps the body feel full.
Retatrutide acts on GLP-1 as well as two additional receptors, which is why it is known as a “triple agonist”.
Fatigue was the next most common complaint, appearing in reports from 1,188 users — around 15 per cent of the group.
Among digestive symptoms, nausea was reported most often, affecting fewer than one in 10 users. Diarrhoea and vomiting were also mentioned, alongside food cravings in 571 reports and insomnia in 475.
The researchers stressed that the findings must be interpreted carefully because they could not independently confirm the identities of the Reddit users, whether they had taken retatrutide or the accuracy of their accounts.
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Even with those limitations, specialists say the results highlight the potential dangers of obtaining retatrutide outside regulated medical channels.
“I would urge people to avoid buying unlicensed weight-loss products online,” Naveed Sattar, professor of cardiometabolic medicine at the University of Glasgow, told Our News Outlet.
‘There is no certainty about what these products contain, and without proper regulatory oversight there is a risk of adverse effects.
‘People may inadvertently do themselves more harm than good by taking substances that have not been rigorously tested for safety and efficacy.’
Some of the most concerning complaints flagged involved changes to the heart and mental health.
A total of 374 users said their heart rate had increased, which is around 5 per cent. Meanwhile, 475 reported insomnia and 301 (fewer than two per cent) flagged anxiety.
Another 206 reported anhedonia – the term for no longer finding joy or pleasure in things you used to enjoy – while 68 reported depression and 64 said they had suffered panic attacks.
Elsewhere, small numbers of patients (55) reported a burning sensation in their skin while 58 said they had developed an intolerance to alcohol.
Other effects impacting smaller numbers included binge eating, decreased libido, obsessive thoughts, nicotine dependence and emotional distress.
There were, however, some more positive changes.
A total of 175 of the 13,589 users said they could exercise for longer, 164 reported an increased libido and 149 said they felt euphoric.
The authors stressed that the study cannot prove the drugs cause these problems.
‘The social media users studied here may not represent all retatrutide users, and adverse events may be preferentially reported,’ the scientists said.
They added that information such as the product’s contents, dose and the patient’s medical history could also not be verified.
While retatrutide targets three receptors, Mounjaro, on the other hand, targets two. Both drugs are made by the same manufacturer, Eli Lilly.
There is an expectation that it could be available to buy in Britain, and even be prescribed by the NHS, within three years.
Eli Lilly was approached for comment.
