The use of an unapproved drug dubbed the 'Godzilla' of weight-loss jabs is raising alarm among doctors, who warn the UK is witnessing a 'huge, unregulated human experiment'.Retatrutide, known as 'Reta', is an appetite-suppressing medication like Mounjaro and Ozempic. But, unlike those drugs, it is still undergoing clinical trials, meaning it has not been approved by health officials.However, soaring demand for weight-loss injections - now believed to be used by around 2.5 million Britons - has fuelled a booming black market for the new drug. Trials suggest that retatrutide can help patients lose up to a third of their body weight in less than a year, prompting people to buy the drug from unlicensed sellers despite the risk that the products could be fake, contaminated or wrongly dosed.Though it is not expected to receive official approval until later this year or early next year, investigations have found TikTok influencers, spas and beauty clinics selling retatrutide online under secret codenames to avoid detection by authorities. The drug is said to be particularly popular with gym-going young men, with early research suggesting it may help patients lose fat while retaining muscle mass. But doctors are now warning that, without official approval, those currently using retatrutide are putting themselves at serious risk.It comes just weeks after health officials in Australia revealed six people had been hospitalised with severe liver damage after taking unlicensed doses of the drug. Retatrutide is an appetite-suppressing medication like Mounjaro and Ozempic - but unlike those drugs it is still undergoing clinical trials