It was with deep dismay that I read the letter from Dr Evan Harris MP et al (November 25) urging the government to postpone plans to reclassify cannabis. The writers say that the level of cannabis use has fallen in recent years, but among young teenagers drug use continues to rise, and the choice of 14- to 15-year-olds is still cannabis.

The brain does not finish its development till the 20s, so the younger a person starts using cannabis, the higher the risk of becoming addicted, suffering mental illness or moving on to other drugs. Dr Harris et al claim that there is no new research, but currently Professor Robin Murray is finding that giving THC - the active ingredient in cannabis - to healthy volunteers does indeed cause psychosis, it's simply a matter of the amount given.

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