Horse tranquilliser Xylazine, which has caused people to rot from the inside out in the US, was found in modified e-cigs seized in Luton, Bedfordshire.
The Health and Social Care Committee was told that headteachers in England are being forced to monitor toilets due to the number of children using e-cigarettes.
EXCLUSIVE: Two were put down to heart disorders, including one cardiac arrest, health chiefs said. Respiratory complications were blamed for the others, with one caused by inhalation of fat.