A blockbuster slimming drug is triggering disturbing mood changes in users – with some claiming the injection has helped them shed weight but left them emotionally 'dead.'

The experimental drug retatrutide, known by some users as 'reta', is so powerful it has gained the nickname 'the Godzilla shot'. It has helped patients lose a quarter or more of their body weight in clinical trials but has yet to receive the green light from the Food and Drug Administration.

Despite this, users have flocked to purchase it on the black market, prompting regulators to warn that unapproved versions sold online may pose serious health risks.

Now, the Daily Mail has uncovered an alarming and severe side effect potentially linked to the drug.

On Reddit, retatrutide users detail their harrowing experiences, with many saying that, since starting the shot, they have been 'unable to experience joy or happiness,' calling the feeling 'genuinely unbearable.'

Meanwhile on TikTok, users have created videos claiming the drug turned them into 'emotionless robots.'

'Yeah, reta was cool until my soul... just disappeared,' one person posted on TikTok.

This phenomenon - known as anhedonia, or emotional blunting - has been previously reported by some patients on newer injectable weight loss medications, including semaglutide (Ozempic, Wegovy) and tirzepatide (Mounjaro, Zepbound). Meanwhile, some patients who have taken those drugs without issue say they have been severely affected after switching to retatrutide.

One such person is Tian Molnar, who has now revealed the 'severe mental health side effects' she experienced that made her 'lose it.'

While she already had a slim figure, 26-year-old beautician and salon owner from Australia still wanted to lose a few pounds, using weight loss drug 'on and off' for three months at a dose of 20mg every five days.

'I had heard a lot about its effects on appetite and weight loss and was curious to see whether it would work for me,' she told the Daily Mail.

Tian claims she noticed 'some benefits' – her physique 'improved' and it helped suppress her appetite – but felt they did not outweigh the downsides.

'Over time, I noticed significant changes in my mood and motivation,' she said. 'I felt unusually tired, flat and extremely unmotivated, and I experienced periods where I felt very sad and insecure.

'There were times when things I would normally enjoy didn't give me the same feeling of happiness or excitement. 

'It was difficult to pinpoint at first because I didn't immediately associate how I was feeling with the medication, but looking back, the change was quite noticeable.' 

These symptoms affected every part of her life: her work, her time at the gym and her relationship with her boyfriend, family and friends. The mental health decline was her 'rock bottom,' she added. 

'The experience made me realize that feeling mentally well and like myself is far more important than losing a few extra kilos,' she said. 

Tian hopes to bring awareness that the potential effects of reta may not just be physical, advising anyone experiencing them to quit the shots rather than 'try to push through.'

'It's not worth your mental health, particularly when people are using these medications for relatively small amounts of weight loss,' she said.

So, what is the truth about this bizarre 'side effect' – and, as regulators move to offer retatrutide to millions more patients across America, could many people be at risk? 

New weight loss drugs work by mimicking the effects of gut hormones that act on appetite centers in the brain, making people feel less hungry and reducing cravings.

Semaglutide targets a hormone receptor known as GLP-1, while tirzepatide acts on GLP-1 as well as a second receptor, GIP.

The drugs also appear to dampen the brain's reward response to food, meaning patients may get less pleasure from eating, while slowing the rate at which food leaves the stomach can help them feel fuller for longer.

Retatrutide goes a step further, adding a third target – the glucagon receptor – to GLP-1 and GIP. This triple action not only suppresses appetite but may also increase the amount of energy the body burns, helping to explain the dramatic weight loss seen in trials.

Patients taking retatrutide lose on average 24 to 28 percent of their body weight, depending on the dose and length of treatment.

By comparison, studies of semaglutide have shown weight loss of around 15 to 17 percent of body weight, while patients taking tirzepatide have lost around 20 to 22 percent.

Anhedonia is not currently listed as a known side effect of these drugs, and there is no evidence proving that the medications directly cause the condition. However, patient reports of emotional blunting or a loss of pleasure while taking the drugs have prompted researchers to investigate their potential effects on the brain's reward system.

Central to this is dopamine, a brain chemical involved in motivation, learning and our response to rewarding experiences. Normally, dopamine is released in response to something the brain considers pleasurable – from eating a delicious meal to having sex – helping to reinforce the desire to repeat that behavior.

But the same system is also involved in cravings and compulsive behaviors. 

Pleasurable foods – particularly those high in fat and sugar – as well as alcohol, nicotine and other drugs, can stimulate these dopamine pathways, triggering the urge to seek them out again. 

GLP-1 drugs appear to interfere with this reward process. The medications act on receptors in areas of the brain involved in reward and can alter dopamine signaling, potentially making food less enticing and weakening the powerful cravings that can drive overeating.

Many patients describe this as the disappearance of 'food noise' – the persistent thoughts about what and when they are going to eat that previously dominated their day.

Intriguingly, the effect may extend beyond food. Some patients taking the drugs have reported losing their desire to drink alcohol or smoke, while clinical studies have begun to find evidence that GLP-1 drugs can reduce reliance on addictive substances such as cocaine and opioids. 

Scientists are now investigating whether anhedonia could, in a small number of patients, be an unintended consequence of this effect.

The theory is that if the drugs dampen the brain's response to rewards strongly enough, they could potentially blunt not only unhealthy cravings but also the pleasure or motivation associated with everyday experiences – from socializing and hobbies to intimacy and romantic relationships. 

Speaking to the Daily Mail, Dr Mary Sco, a physician with a special interest in nutrition, says: 'GLP-1s blunt the amount of dopamine that's being released in the brain when we eat.  

'If we're blunting that dopamine response, decreasing our cravings and reducing the amount of pleasure we experience from food, it could potentially blunt the pleasure we experience from other things in life as well.

'So I'm not at all surprised that someone might say their attraction to others, or their interest in things generally, has decreased.'

Dr Sco added that, in theory, retatrutide could cause more severe anhedonia than other weight-loss drugs because it targets more hormonal pathways and appears to have a more powerful effect.

There is also some evidence the effect may be dose-related. A recent report described three women taking the highest 15mg dose of tirzepatide who developed emotional flatness and lost interest in activities they previously enjoyed. Their symptoms improved after reducing or temporarily stopping treatment.

Sco advises doctors to start patients on the lowest possible dose and increase it gradually.

Some retatrutide users have also reported a lower sex drive alongside anhedonia, with one Reddit user claiming it had 'completely destroyed' their libido. Sco agreed this was plausible.

'Dopamine helps drive human desire and attraction, and GLP-1s can influence dopamine signaling in a way that reduces reward-driven behavior. So, theoretically, GLP-1s could also reduce sexual desire,' she said. 

However, there is currently no evidence GLP-1 drugs reduce libido. Sco says improved metabolic and cardiovascular health could, conversely, improve sexual function.

A 2024 study found GLP-1 drugs could potentially be associated with a 51 percent lower risk of erectile dysfunction.

Some users even say the emotional flatness has been beneficial.

'I can feel what people mean when they say they feel "flat" or not as passionate about regular things. But for me that's actually turned into a positive,' one Reddit user wrote.

The man said retatrutide had reduced the pleasure he got from partying, drinking, smoking weed and 'binging on sex,' allowing him to focus on his fitness goals.

'It's helped me control cravings, whether it's for snacking, drinking, or having sex.'

Eli Lilly is conducting Phase 3 trials of retatrutide and plans to file for FDA approval in the first quarter of 2027. However, the pharmaceutical company announced Tuesday that a limited number of patients with an acute clinical need will be able to apply for early access.

Health officials and Eli Lilly have repeatedly warned that products sold online purporting to be retatrutide are counterfeit and potentially dangerous.

Jill Ketner Villa, Physician Associate and founder of Goldhaus Wellness, told the Daily Mail: 'Quality matters, and if you don't know exactly what's in the vial, you can't confidently attribute either the benefits or the side effects to the medication itself.

'Dose variability, contamination, or even the wrong compound altogether become real possibilities.'