From The Financial Review last week.

Few still believe the old myth that smoking marijuana leads to a spiral of drug dependence and dissipation. Some claim prolonged use can adversely affect the mental health of certain individuals, and it certainly has the potential to make driving dangerous, but compared to alcohol it is a drug of peace and tranquillity.

That being the case, it is difficult to understand why marijuana remains prohibited. It is especially bizarre that its medical properties cannot be utilised.

These properties have been known for a long time. Chinese Emperor Shen-Nung wrote of the medicinal properties of the cannabis plant in the 28th century BC. The ancient Egyptians used medical cannabis extensively four thousand years ago, and the diuretic, antiemetic, antiepileptic, anti-inflammatory, analgesic and antipyretic effects of cannabis were well known in medieval medicine.

In the early 20th century, before it was banned, numerous tonics and tinctures containing cannabis extract were available. More recently, studies have confirmed the effectiveness of the active ingredients for treating conditions such as glaucoma, migraine and arthritis, providing relief from chronic pain associated with degenerative diseases and spinal injuries, and alleviating the unpleasant side effects of common treatments for cancer and HIV/AIDS.

Its relative safety, long recognised in folk wisdom, has also been borne out by research. When taken as an oral tincture, cannabis-based therapies are not only safe for children but beneficial in treating the frequency and severity of seizures associated with childhood epilepsy.

Despite its continuing prohibition, attitudes are changing. The 2007 National Drug Strategy Household Survey reported that 70% of respondents were in favour of legalising marijuana for medicinal purposes while 75% were in favour of further clinical trials. In 2013 the NSW Legislative Council’s inquiry into the use of cannabis for medical purposes concluded there was sufficiently robust evidence to support its use as a treatment option for certain conditions.

The rest of the world is changing faster though. Medical marijuana is already legal in Austria, Canada, Finland, Germany, Israel, Italy, the Netherlands, Portugal and Spain, and under state laws in more than twenty US states. In two of those, Colorado and Washington, recreational use is also legal.

The quest for additional taxation revenue is one of the reasons for this. Colorado, for example, expects to generate US$133 million in taxes annually. Both medical and recreational sales are subject to a 2.9% sales tax, while recreational sales are also subject to a 10% sales tax and 15% excise. The vast majority of the revenue is expected to come from recreational marijuana.

There are many reasons why marijuana should be legal, especially for medical reasons. It is unconscionable to deny people an effective, safe solution for chronic pain, for example. There is no doubt it helps some conditions when nothing else works. It would also be cheaper than most current therapeutics.

The cultivation of cannabis on a commercial scale, along with the preparation and dispensing of medical marijuana, has the potential to generate significant employment. The largest cannabis dispensary in Oakland, California (a third the size of Perth) has over 104,000 customers and employs 120 people.

There is also scope to expand our burgeoning biomedical sciences sector, with particular regard to creating innovative delivery systems such as cannabinoids in lozenge, vapour and tincture form.

Legal availability would deprive organised crime, including some bikie gangs, of a major source of income and relieve police of the cost of finding and destroying illicit crops. Of the $1.5 billion spent annually on drug law enforcement, 70% is attributable to marijuana. State and federal budgets would benefit from reassigning police to catching criminals who harm and defraud other people, and many otherwise innocent people would be spared a criminal conviction.

Legalisation of recreational use would also acknowledge the reality that most people have tried it, legal or not, at some point in their life, me and President Obama among them.

I do not recommend the use of marijuana except for medical purposes, but ultimately whether it is used for medical or recreational purposes should be a matter for adults to decide for themselves. Whether others approve, or would choose it themselves, is not relevant. It is especially not the business of the government.

As the father of liberalism, John Stuart Mill, put it, “But it is not legitimate, for government to involve itself in things that a person voluntarily does to him or herself, or that people choose to do to each other by mutual consent, when nobody else in harmed.”

Mill was not thinking of marijuana when he wrote that, but he could have been.

David Leyonhjelm is the Liberal Democrats’ Senator-elect for NSW.