Endless newspaper reports link cannabis with suicides, murders and assaults. The headlines are dramatic: "Another cannabis teenager in knife killing: Boy on skunk butchered a grandmother"; "Get tough on skunk or more will die"; "Cannabis addiction soars as drug gets stronger"; and so on.

Is this a case of ‘moral panic’, or are concerns about the mental health effects, amid claims that cannabis is as much as 20 to 30 times stronger than in the past, justified? Did the reclassification of cannabis from Class B to C send out ‘the wrong message’ that it is safe, or at least less harmful than before?

Cannabis is a potentially harmful drug. A few years ago, I heard an advocate for cannabis legalisation claim that the worst that can happen if you smoke too much is fall asleep. Does anyone today believe such nonsense? The Independent on Sunday, which had campaigned for the drug to be decriminalised, doesn’t: it declared an about turn with the front page headline:
"Cannabis, an apology".

In July the Prime Minister announced a review of cannabis classification, the second since the drug was reclassified in January 2004. The Government’s expert advisory body, the Advisory Council on the Misuse of Drugs (ACMD), reviewed the evidence two years ago and recommended the status quo. But the Home Secretary, in her recent letter to the Chair of the ACMD, said, "There is real public concern…in particular the use of stronger forms of the drug, commonly known as skunk."

It was also reported in July that a new study, published in The Lancet, found that cannabis users are 40 percent more likely to develop a psychotic illness and that smoking just one joint a day could double the risk of schizophrenia. Surely compelling and persuasive evidence that the harmfulness of cannabis has been underestimated? Well, it would be if the reports accurately reflected what the authors of the study concluded. Echoing the findings of the ACMD in 2005, the study found a consistent association between cannabis use and psychotic symptoms (sufficient to highlight the risks) but emphasised that an association does not establish causation.

Cannabis can worsen mental health problems or trigger relapse and may for a small proportion of the population trigger the onset of serious problems. But many people with mental health problems use cannabis to self-medicate, to relieve the symptoms of their condition or the effects of medication. Over 10 million adults (between ages 16 and 59) have used cannabis with around 3 million having done so in the past 12 months. The vast majority have not come to obvious harm, but quantifying those who do is fraught with difficulties. As yet, there is no evidence to confirm that the incidence of schizophrenia has increased in the last 30 years, despite a significant increase in cannabis use.

The cannabis market in the UK has changed substantially, which may explain why (not least among our politicians) there is the belief that the drug is ‘different’ from what it used to be and inevitably more potent. Ten years ago about 90 percent was imported, with cannabis resin (mostly from Morocco) dominating. Today up to 60 percent is grown here in the UK and sold in leaf or ‘herbal’ form. But not all ‘herbal’ cannabis is skunk (sinsemilla), indeed gangs responsible for many of the UK’s cannabis factories tend to use faster-growing, less potent plants. The average THC content (the main psychoactive constituent) of skunk has doubled over the last ten years or so and is on average twice as potent as resin: a worrying increase, but not of the magnitude some claim.

Cannabis is a harmful drug and reclassification did cause some confusion. But based on the overall harms caused, and compared with some other drugs (legal and illegal), it is not our greatest problem, yet it receives disproportionate media and political attention.

Since reclassification, levels of use have actually fallen, particularly among young people, although patterns of use can change. The latest review matters because it will test whether drug policy is proportionate and evidence-based, or driven (even in part) by media headlines and political considerations.

Martin Barnes is Chief
Executive of DrugScope