Cannabis is a harmful drug. While this may sound a statement of the obvious, it was not so long ago that some “pro-cannabis” campaigners claimed that the drug was virtually harmless and a national broadsheet newspaper campaigned for the drug to be legalised. But in light of the decision to reclassify cannabis back to class B, has the pendulum swung too far the other way? Despite the fact that the number of people using cannabis has continued to fall since the drug was reclassified to C in January 2004, there has been no let-up in alarmist media stories linking cannabis with serious assaults, murders and suicide.
The Advisory Council on the Misuse of Drugs (ACMD) has reviewed cannabis classification twice in four years. The decision to reclassify back to B, against the advice of the ACMD, was justified by the Home Secretary as a precautionary measure because of concerns about increased cannabis potency. She told the House of Commons that she also took into account the view of the public, citing the fact that 58% of those surveyed in an opinion poll (commissioned by the ACMD) said that cannabis should be class B or A.
The Home Secretary omitted to mention that in the same survey, when asked what penalties should apply for cannabis possession, 68% of those polled said offenders should serve either 2 years’ imprisonment (the maximum sentence for class C) - or that there should be no penalty at all. These contradictions suggest a level of misunderstanding about the drug classification system as a whole.
One of the clear 'messages' sent out by this decision is that drug policy can be informed as much by media headlines and politics as by an objective approach to the evidence. 
There is no doubt that the cannabis market in the UK has changed over the last decade. The availability of cannabis resin has fallen, while that of more potent forms of herbal cannabis such as “skunk” has increased. Yet despite alarmist claims that cannabis is 20 to 30 times stronger “than it used to be”, the evidence shows that the potency of herbal “skunk” cannabis has increased by 2 to 3 times since 1995. While this does represent a clear and worrying rise in potency, it is not of the order suggested by some. Further research is needed to understand what impact this increase in potency has on the user.
There is now clear evidence that the use of cannabis can worsen mental health problems and cause relapse in those with existing problems. However, recent concern (and controversy) has centred on whether cannabis can trigger the onset of psychotic illnesses, including schizophrenia. The research does point to an association between cannabis use and the later onset of psychotic illness but establishing cause and effect is very difficult.
Cannabis is by far the most commonly used illegal drug, with prevalence highest in the 16 to 24-year-old age group – the onset of schizophrenia in males is highest between the ages of 20 and 24. We also know that many people with mental health problems use drugs such as cannabis to relieve symptoms or self medicate. Despite a substantial increase in cannabis use over the last 30 years, there is, as yet, no evidence of an increase in the incidence of schizophrenia in the general population.
Of course, the effects of cannabis use on physical health should not be overlooked - when smoked, the drug can damage the respiratory tract and lungs. For heavy users, it may decrease sperm counts and suppress ovulation. The physical withdrawal symptoms experienced by those with a dependency can include weight loss, muscle pain and insomnia.
However, figures show that across England and Wales, nearly 11 million adults have used cannabis at least once; over three million people have used it in the past 12 months. Working on the evidence currently available to us, we have to conclude that the vast majority of these people come to no obvious harm. For its latest review, the Advisory Council spent three full days considering the evidence on cannabis harms. The Council concluded that although the drug “poses a real threat to the health of those who use it”, there was insufficient evidence to show that it is as harmful as other drugs in class B, such as amphetamines.
Other than a stepping up of enforcement after a first possession offence, it is unclear what the decision to reclassify will achieve - there is no evidence that reclassification upwards will reduce levels of use, availability or levels of harm. Much has been made of the need to “send out a strong message” on cannabis use. One of the clear “messages” sent out by this decision is that drug policy can be informed as much by media headlines and politics as by a calm, robust and objective approach to the evidence.
www.drugscope.org.uk
Author's competing interests: MB sits on sits on the Advisory Council on the Misuse of Drugs