Vaping-related illnesses have now claimed the lives of four people with hundreds falling sick.
As many as 450 people across 33 US states have come down with lung illnesses related to use of the electronic devices, health officials announced today.
Although only 215 cases have been confirmed by the country's Centre for Disease Control and Prevention, speculation is rife that the numbers are much higher.
A wide-reaching investigation has now been launched. It is thought that many of the illness are related not to nicotine based liquids smoked through e-cigarettes, but to THC vaping.
THC is the active substance in cannabis and is now readily available in e-liquid form in many states that have legalised the drug.