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The German government has 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 , unlike many western countries – including , and several states in the US – which have opened up access to cannabis in recent years.

The UK government 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 because to run such studies would be unethical.

There is, though, a 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 will have quality control as part of their ethos, providing information about potency and any potential contaminants.

This is important as the suggests there is a – an association between the amount consumed and the incidence of effect – between the 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 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 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 it with tobacco to smoke. The risks to health as a result of using tobacco are well and include a range of cancers as well as heart disease and stroke.

Although 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 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 ³Ô¹ÏÍøÕ¾ Statistics 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 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 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 cannabis could bring in significantly higher financial returns.

The 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.

Mark Monaghan receives funding from UK Government, Cabinet Office and the ESRC. He has in the past received funding from the Nuffield Foundation.

Ian Hamilton does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.