Fentanyl addiction has swept across North America where the drug and other synthetic opioids have been blamed for thousands of deaths. It hit the headlines here when it was linked to a spike in fatalities in certain parts of the UK after being mixed with heroin.

Allan Urry travels to Stockton on Tees where ten deaths have been linked to Fentanyl and its derivatives. He meets users and their families and the medical professionals and police dealing with the problem.

But while Fentanyl is currently in the spotlight, it is tranquilisers and other sedatives often used by heroin users to dull withdrawal symptoms which are contributing to many more deaths. Nowhere is the problem more acute than in Scotland where benzodiazepines contributed to nearly half of all drug deaths.

Many of the pills known as "street valium" or "blues" are made in back street laboratories run by organised crime gangs. Users gamble with their lives as the ingredients and strength of the tablets are often unknown.

But File on 4 has discovered that organised crime gangs have also become involved in diverting significant numbers of highly addictive medicines from the legitimate supply chain onto the black market.

Regulators say there is an extensive network of criminality involving businesses such as wholesale dealers and registered pharmacies. Some in the pharmaceutical industry such as drug manufacturers are repeating calls for supply chain regulation to be reviewed to ensure medicines reach their intended target.

Reporter: Allan Urry

Producer: Paul Grant

Editor: Gail Champion.