ADVICE ON CANNABIS IS BASED ON EVIDENCE

Debra Bell (Letters, November 27) is wrong to imply that cannabis use
is on the increase or has become the norm since the government
downgraded it to class C in 2004, in line with the advice of the
Advisory Council on the Misuse of Drugs. Evidence from the National
Centre for Social Research suggests a fall in reported use of cannabis
in the 11- to 15-year-old age group, from 13.4% to 9.4% in the years
2001-07. Evidence from the British Crime Survey suggests that in the
16- to 24-year-old age group use has declined from a peak in 1998 of
28.2%, to 20.9% in 2006-07, with the sharpest falls following
downgrading.

In its recent assessment the ACMD considered all the latest research,
including studies focusing on THC and psychosis. Those studies do not
provide evidence of a significant or extensive causal link between
cannabis use and persistent psychotic symptoms or schizophrenia.
Moreover, the fact that such research has ethical approval indicates
that the researchers and their regulators are confident that this is
not going to happen.

Over-focusing on cannabis classification distracts from the need to
offer proper education to young people and to appropriately police and
punish the suppliers of illegal drugs.

Ms Bell argues that the role of the drug classification system is to
"give comfort" or to "send a message". This is not the case - the drug
classification system categorises substances based on their relative
harm. It is the duty of scientific advisers to government to describe
the evidence as it is, not as lobby groups would want it to be.

Professor David Nutt