A significant increase in cannabis smoking is leading to serious mental health problems among the young, two leading drugs experts said yesterday. They warned that the effect of cannabis on the body was equal to cigarettes but was "far more dangerous" on the mind. Prof John Henry, a toxicologist at Imperial College, London, said: "Regular cannabis smokers develop mental illness. "There is a four-fold increase in schizophrenia and there is a four-fold increase in major depression and that is something very, very different to what cigarettes do to you." Dr Ian Oliver, independent consultant to the UN Drug Control Programme,...