There was a show about that research on pot tv, they interviewed kids that say- im addicted to cannabis, and if i dont have a spliff i get mad and cant sleep.One kid said i hear voices talking to me, having the most random conversations.They said the popular strain most common in the UK is Skunk, this strain is said to cause serious mental health issues in young people-psychotic,skitzophrenic,demented and poluted kids claim that cannabis is the main cause of there mental health problems.