Illegal drug use is here to stay. Human beings have used mind-altering chemicals for at least as long as we've cultivated crops, and if the US experiment with prohibition of alcohol in the 1920s taught us anything, it's that criminalizing a product with such huge demand will do very little to stop people using it.

The UK leads Europe when it comes to the use of illegal drugs, topping the charts for cocaine, ecstasy, amphetamines and LSD, and coming second for cannabis use. As in most countries, there is a classification system for illegal drugs, from class A to class C. Class A drugs are supposedly the most dangerous and carry with them the harshest penalties for possession or distribution. Heroin and cocaine are both class A, barbiturates are class B and cannabis and steroids are class C. But as with many countries' classification schemes, the harm that these drugs can do to users and societies doesn't often match up with their legal status.

Now, a new paper published in The Lancet has looked at this issue and has put together a more rational scale to assess the relative levels of harm from drugs, both legal and illegal. The work was carried out by a cross-disciplinary group of rather eminent scientists, including Prof. Colin Blakemore, the head of the Medical Research Council (equivalent to the NIH). The study involved surveying two groups; a national group of leading psychiatrists, and a more general group made up of experts from a range of disciplines including forensics, pharmacology, the police and legal services, chemistry, and epidemiology.

The surveys were designed to rate drugs for harm for three different categories, on a scale of 0-3, with 3 being most harmful. Then an overall mean was taken. The categories were physical harm, dependence, and social harm. The first group of psychiatrists assessed the following drugs; heroin, cocaine, alcohol, barbiturates, amphetamine, methadone, benzodiazepines, solvents, buprenorphine, tobacco, ecstasy, cannabis, LSD, and steroids. You'll note both tobacco and alcohol on that list. In the words of the authors' "Tobacco and alcohol were included because their extensive use has provided reliable data on their risks and harms, providing familiar benchmarks against which the absolute harms of other drugs can be judged. However, direct comparison of the scores for tobacco and alcohol with those of the other drugs is not possible since the fact that they are legal could affect their harms in various ways, especially through easier availability."

The second group looked at the same drugs, and also khat, 4-methylthio- amphetamine (4-MTA), gamma 4-hydroxybutyric acid (GHB), ketamine, methyl phenidate, and alkyl nitrites, some of which are not illegal in the UK but are still misused. As you can see from the graph, in the opinion of these experts, some of the drug classifications are spot on, such as cocaine and heroin, but others are a surprise. Alchohol ranks number 5, despite being perfectly legal, whereas ecstasy, currently a class A drug, is one of the least harmful.

The paper highlights the failings of the current Misuse of Drugs Act, and although they do not suggest that alcohol or tobacco ought to be criminalized, from a scientific perspective they "saw no clear distinction between socially acceptable and illicit substances. The fact that the two most widely used legal drugs lie in the upper half of the ranking of harm is surely important information that should be taken into account in public debate on illegal drug use."

The fact that the UK home office did downgrade cannabis from class B to C recently suggests that the UK government is at least open to the idea that their drugs policies might not have been working. Whether or not the same message will get through to US lawmakers seems unlikely to me. Although the "war on drugs" in the US is having devastating consequences on certain sections of US society, its also very big business for law enforcement, private prisons and other associated interest groups. You can consider me firmly in The Economist's camp, along with Milton Friedman, who in my opinion got at least one thing right in his career.