The Prime Minister recently, in light of recent evidence that certain strains of cannabis can cause mental illness in some users, asked the Advisory Council on the Misuse of Drugs (ACMD) to reconsider the decision in 2004 to downgrade the drug from class B to class C. The consultation on reclassifying cannabis is part of a review of the entire UK drugs strategy. The problem is, the legal classification of drugs is an exceptionally detailed business.

The classifications are laid out in schedules to the 1971 Act. Class C, the lowest category, includes substances such as anabolic steroids; class B, includes drugs such as amphetamines; and class A includes opium and cocaine. The higher the class, the more serious the offence.

Such regulation of substances presents very tricky challenges to the law for two main reasons:

First, the science on which the classifications are made is always developing, as are the drugs themselves. During the last 100 years, cannabis has gone from being legal to illegal, then graded as a middle-ranking drug, then downgraded. Now it seems set to be re-graded back to the middle bracket. Before 1977, when the law was changed, the chemically-engineered drug Ecstasy was not unlawful.

Second, social attitudes and political winds change. In the 17th century, coffee houses were seen as dens of iniquity. Now the High Street is clogged with them. The drug amphetamine sulphate (speed) wasn’t seen as a degenerate or dangerous for much of last century. It was taken as a pep by all sorts of people including soldiers, film stars and housewives. Then policy changed and it became a controlled drug in 1964.

The way the law divides legal and illegal substances isn’t based exclusively on pharmacological knowledge. It is too simplistic to see illegal substances as bad and legal substances as generally good. One only has to consider that alcohol has been responsible for over 300,000 deaths in the past 10 years. Caffeine has been clinically recognised as more addictive than morphine. (As Milton Berle noted: “I had a friend who drank twenty cups a day at work. He died last month, but a week later he was still mingling in the company lounge”.)

The back story to the criminalisation of cannabis shows that it was not universally seen as a health hazard. The Hague Convention of 1912 (an international governmental agreement about opium), aimed to stop organised crime from getting into the business of drugs distribution. But while the use of drugs was commonly seen as a weakness or vice, it was not seen as criminal. In 1914, the US passed legislation putting a nominal tax on the supply of opium through pharmacies – once cent per ounce. The aim of the law was simply to get drug distribution formally recorded and registered; it didn’t make consumption illegal.

In Britain, the Dangerous Drugs Act 1932 said that “any extract or tincture of Indian hemp” – in other words, marijuana - was a substance whose manufacture, import and export should be prohibited unless licensed.

It wasn’t until 1937 in the US that the first major and dedicated legislation on cannabis was introduced. It only became federal law after the legislature credulously accepted evidence such as the virulently racist contributions of Harry J. Anslinger, the head of the Federal Bureau of Narcotics. Mr Anslinger contended that most crime was being committed by "coloureds" with big lips, luring white women with "voodoo-Satanic" music (jazz) and marijuana.

The legislation was promoted by the Bureau of Narcotics, which was keen to expand its areas of operation. The law was passed without substantial debate. In the Congressional hearings in April and May 1937 (in a committee of the legislature), the representative of the American Medical Association, Dr William C. Woodward, challenged the Bureau’s contentions that marijuana was harmful to health and in widespread use among children; he asked for the evidence behind such claims but he was given no answers.

Today, there are various views on where to draw the line of legality on intoxicants and mind-altering substances. Opinions range from advocacy of a prohibition on all substances to advocacy of unrestricted legalisation. Perhaps the only sort of statement that would attract universal acceptance is that of the rapper Eminem: “Never take Ecstasy, beer, Bacardi, weed, Pepto Bismol, Vivarin, Turns, Tagamet, HB, Xanax, and Valium in the same day. It makes it difficult to sleep at night.”

Professor Gary Slapper is Director of the Centre for Law at The Open University

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