The push for recreational cannabis legalisation in Australia has recently received energetic support from Dr Di Natale and his band of Greens. Renewed calls for the liberation of the weed follow in the wake of Israel, Canada, nine US states and some other jurisdictions moving towards legalisation. The Greens would like government monopolisation of both the production and sale of the drug. According to their proposal, regulatory authorities would ensure that the licensed product is safe, of consistent quality, and is advertised and packaged appropriately.

Medical marijuana has been legal in Australia since 2016. Although we must be cautious about overstating its therapeutic qualities, there is evidence that cannabis is beneficial in certain kinds of epilepsy, pain disorders and possibly even in the treatment of opiate dependence. As in the UK and much of the US, recreational use is still illegal in Australia. A majority of Australians oppose legalisation.

In a Green Utopia, users would be spared the social and financial consequences of criminal prosecution. Minor cannabis offenders in Australian states are currently diverted away from the legal system, so decriminalisation has been the de facto status quo here for a while. Police are already ambivalent about enforcing existing laws and tend to issue cautions to those in possession of small quantities. If there has been a ‘war on drugs’ in Australia, the heavily artillery of massive health promotion and user stigmatisation have primarily targetted tobacco. (That being said, the government is quite comfortable stinging users with a crippling consumption tax; a regressive measure that hits the poor the hardest).

In keeping with a harm minimisation approach, activists are quick to reassure sceptics that the spoils of a ‘cannabis tax’ will be directed towards the prevention and treatment sector. This is classical socialist thinking; create the problem then employ a workforce to ‘solve it’. Legalisation proponents claim that law enforcement agencies could then direct their energies and funds towards chasing the black marketeers. We are told that with the projected net revenue for legalisation could top $700 million. It all sounds great, right? Australia could be the next frontier in pot tourism.

Libertarians argue that current laws infringe civil liberties. As long as nobody else is adversely affected by our actions, shouldn’t we be free to smoke whatever we wish? But the reality is that in a welfare state some of us have to pay for our neighbours’ bad choices. Since it is unlikely (but not undesirable) that we will have a Nozickian minimal state anytime soon, the benefits of legalisation of pot to the community must outweigh the social and financial costs.

This is why the Greens, usually silent on matters economic and largely indifferent to the plight of the taxpayer, boast of the financial windfalls we might expect if the laws were to change.

In order for legalisation to work, and if the Canadian experience is anything to go by, government-grown cannabis will need to be cheaper than the illegal stuff for it to be the first choice of smokers.

Additionally, the ‘official pot’ will be less potent than the varieties to which smokers are currently accustomed. The government will be forced to compete with the underground market whilst at the same time having to set prices that ensure that sufficient tax revenue can be generated.

It is plausible that in the event of legalisation, many users will still opt for the ‘dirty’ product.

Let’s be clear; cannabis is not benign. The effects of marijuana on the developing brain can be catastrophic and irreversible. The UK’s pre-eminent schizophrenia expert, Professor Sir Robin Murray, wrote in the Guardian that cannabis is ‘the most preventable risk factor for psychosis’.

We know that regular cannabis use doubles the rate of schizophrenia. It has been estimated by the Australian Institute of Health and Welfare that amongst people who used the drug recently, 16 per cent smoke cannabis daily. This percentage is likely to be much higher in our remote indigenous communities where many children and teens are continually intoxicated. These ugly facts do not receive enough media attention and should be of greater concern to the public health panjandrums. How many high school students are fully aware of the dangers of cannabis? How many parents shrug their shoulders and dismiss their teenager’s experimentation as a normal part of growing up?

In comparison with alcohol and tobacco, the neuropsychiatric effects of cannabis tend to manifest themselves in early adulthood. Schizophrenia is an affliction of the young; symptoms often first emerge just before the individual is poised to face the adventures and challenges of adulthood. Marijuana smoking brings forward the onset of illness in people with a genetic susceptibility. It is the ‘false friend’ to patients in the first flush of their index psychotic episode because it elicits relaxation and produces a subjective alleviation of symptoms whilst at the same time stoking the fires of psychosis.

It is my experience that only a tiny proportion of patients with cannabis abuse whom I refer end up seeing a drug counsellor, and fewer still engage in any long-term intake reduction. It is often the case in cannabis dependence that both the spirit and the flesh are weak. The nature of addiction is that those who most need abstinence are unlikely to undergo successful rehabilitation unless there are significant costs associated with continued use of the drug.

I freely admit that the decriminalisation of marijuana presents an ethical dilemma. As a psychiatrist I am well aware of the potential harms associated with more widespread use, especially in those under the age of 25 and in other vulnerable populations, but I am loath to support governmental intrusion into personal choices. A 2016 report card by the US think tank Cato on the early outcomes of legalisation in Colorado, Oregon, Washington and Alaska concluded that the effects of changes to the law thus far failed to support the stronger claims of either side in the debate. Time will tell.