The advertisement appears harmless, but it is far from it: isotonitazene is a type of nitazene, a class of synthetic opioids up to 40 times stronger than fentanyl and up to 500 times more powerful than heroin.

Nitazenes were developed in the 1950s by a Swiss chemical company as a new type of painkiller, but the drug was so potent that it was never approved as a medicine. Even trace quantities can cause an overdose.

Decades later, nitazenes have re-emerged in the underground drug market: they have been detected in counterfeit prescription medicines, including fake oxycodone and benzodiazepines pills, and in street drugs, including cocaine, heroin and ketamine.

The UN drugs agency and countries around the world have warned of the major health risks posed by nitazenes. The super-strength opioid has already caused hundreds of deaths in Europe, the UK and North America.