Ian Hamilton, University of York and Mark Monaghan, Loughborough University

The German government has approved new legislation which decriminalises cannabis.

This policy allows over-18s to possess a maximum of 25 grams of cannabis for personal use and grow up to three plants at home.

From July 2024, German residents will also be able to join not-for-profit cannabis social clubs or growers associations where plants are cultivated en masse for the benefit of members.

In the UK, on the other hand, the government continues to support prohibition, unlike many western countries – including Malta, Canada and several states in the US – which have opened up access to cannabis in recent years.

The UK government cites concerns about the risk to mental health associated with using cannabis as a justification for supporting prohibition.

Cannabis and mental health

There is extensive research exploring the relationship between cannabis and mental health problems, such as psychosis. However, no causal link has been established because to run such studies would be unethical.

There is, though, a significant association between cannabis and psychosis. The evidence suggests that some people may be more vulnerable than others to developing psychosis through cannabis use.

Although these health concerns are shared by some organisations in Germany, this has not prevented policy reform.

The German cannabis clubs will have quality control as part of their ethos, providing information about potency and any potential contaminants.

This is important as the evidence suggests there is a dose-response relationship – an association between the amount consumed and the incidence of effect – between the strength and frequency of cannabis use and the risk of developing problems such as psychosis.

Cannabis users who experience psychosis are very few when compared to the total number using the drug. One study estimated that to avoid one person developing psychosis, up to 10,000 men and 29,000 women aged 20-24 would need to be prevented from using cannabis.

The risk to mental health associated with cannabis, then, is relatively low.

Alcohol and tobacco: regulated but riskier

Unlike cannabis, alcohol is regulated in the UK. Although there are restrictions on its use, these have been loosened in recent years. As with cannabis, there are risks to mental health as a consequence of using alcohol.

The risk of developing depression among heavy alcohol use is significant: one in two will experience depression. So despite alcohol being regulated or legal, the risks to a person’s mental health are greater than those posed by cannabis.

A significant advantage of decriminalising cannabis would be the potential public health benefits. In the UK, most people using cannabis combine it with tobacco to smoke. The risks to health as a result of using tobacco are well documented and include a range of cancers as well as heart disease and stroke.

Although many young people consider themselves non-smokers they can be inadvertently introduced to tobacco when they smoke a cannabis joint. This creates not only a health risk but also the chance of becoming dependent on tobacco.

However, there is also evidence that cannabis used without tobacco may increase the risk of physical health problems. A recent study from the US, for example, where fewer people combine cannabis with tobacco, found a link between cannabis use and heart disease.

Because cannabis is prohibited, it is difficult for tax-funded organisations such as those promoting public health to intervene.

Public health

In contrast, German policy reform includes a public health education programme which aims to reduce the risks of using cannabis.

Under prohibition, there is no quality control or information about the potency of cannabis or which chemicals it contains. The lack of regulation leaves buyers at the mercy of the illicit market.

The Office for National Statistics estimates that 2.5 million people in England and Wales reported using cannabis in 2023.

Despite the relatively widespread use of cannabis in the UK, the major political parties, Labour and the Conservatives, show no sign of changing the legal status of cannabis. Perhaps influenced by polling suggesting support for the current policy approach.

We know from experience that governments don’t need to wait until there is public support to change their policy approach to drugs. In 2007, when the Labour government introduced a ban on smoking in public areas, this wasn’t supported by many people.

The risks to health from using cannabis, then, are relatively small compared to regulated drugs such as alcohol and tobacco. But even if the health argument isn’t enough to trigger a policy change, the economic case could be.

While decriminalising cannabis in the UK would save on criminal prosecution costs, going a step further and legalising cannabis could bring in significantly higher financial returns.

The estimated tax revenue that could be raised by the legalisation (rather than just the decriminalisation) of cannabis in Germany is €4.7 billion (£4 billion) annually. A regulated commercial market like Canada’s could create jobs as well as raise income from tax.

As the UK public finances continue to be squeezed, particularly around the NHS, persisting with the prohibition of cannabis is a missed opportunity for the nation’s health and a costly policy for its public services.

Ian Hamilton, Honorary Fellow, Department of Health Sciences, University of York and Mark Monaghan, Professor in Criminology, Loughborough University

This article is republished from The Conversation under a Creative Commons license. Read the original article.