Poll: Should cannabis use be dealt with more harshly by the Criminal Justice System?

Cannabis use can become addictive, cause mental health problems and lead to hard drug use, according to a new study.

The research, carried out over 20 years by Professor Wayne Hall - a British expert on addiction - found that one in six teenagers who regularly smoke the drug become dependent on it.

It concluded that using the drug while pregnant reduces birth weight, while teenage users do worse at school and are twice as likely to be diagnosed with schizophrenia or report psychotic symptoms in adulthood.

Professor Hall, of King's College, London, found that one in 10 of all regular users develop dependence on the Class B drug.

His study, published in the journal Addiction, also found that cannabis smokers put themselves at a higher risk of developing chronic bronchitis, while use by middle-aged people "probably" increased the chances of suffering a heart attack.

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