The study of the lives of more than 5,000 teenagers produced the first resounding evidence that cannabis is a gateway to cocaine, amphetamines, hallucinogens and heroin.
Teenagers who regularly smoke cannabis are 26 times more likely to turn to other drugs by the age of 21.
Ian Hamilton, who is a mental health researcher at York University, said: “It adds to evidence that cannabis acts as a gateway to nicotine dependence, as the majority of people using cannabis in the UK combine tobacco with cannabis when they roll a joint.
“This habit represents one of the greatest health risks to the greatest number of young people who use cannabis.
“It suggests that adolescent cannabis use serves as a gateway to a harmful relationship with drugs as an adult.”