There does not seem to be much rigorous research on this subject. I feel the effect of cannabis on the developing brain of teenagers cannot be overstated, articles always allude to "an increased risk of psychosis" but what this means in reality, the devastation of mental health problems and schizophrenia particularly is never explained or demonstrated.
Our son started experimenting with cannabis when he was fourteen and we feel strongly that this contributed to his developing schizophrenia from about the age of seventeen. It became apparent during his prolonged stay in a psychiatric unit under a section that he was also treatment resistant. Only when he was treated with clozapine which had to be augmented did he begin to stabilise.
The doctor treating him felt that he, in his practice, was seeing more young men like this and he felt that the brain being bathed in these illicit drugs during adolescence was a contributory factor.
Our son managed to procure cannabis whilst in hospital under section and was cautioned and fined for this despite at the time not being deemed fit to make decisions. Fortunately he now no longer smokes cannabis but has to take medication and lives in supported accommodation. He is now 23 years old and is just beginning to have a life again.