One thing that I am certain of after nearly 20 years working as an addiction therapist is that current drug policies in the UK are simply not working.
As a society we have chosen to deal with the problem of drug addiction mainly by banning harmful substances and pursuing users and suppliers through the courts.
Yet our whole approach is perverse to say the least. Why for example, are tobacco and alcohol freely available when combined they probably kill more people than every other illegal substance?
In the case of marijuana, it exists in a kind of legal limbo. Prosecutions for possession of small amounts in the UK are rare, yet its sale is forbidden.
This means that the only outlet for its supply is via the criminal underworld - and that's what makes it so dangerous ...
In one fell swoop we have handed a monopoly over the control and supply of cannabis and its derivatives to drug dealers and criminal gangs.
This means that it has become a gateway drug. When a person goes out to score cannabis they go to a dealer, and it's highly likely that sooner or later the buyer will also be offered harder drugs.
I have met hundreds of addicts who have come into treatment for heroin and cocaine who all began by smoking cannabis.
In my experience, nobody begins using drugs for the first time by injecting smack into their veins. Instead, there is a progression from softer drugs, which escalates into more serious substance abuse.
Cannabis addiction rarely manifests itself in isolation - users will often also have issues around other substances and processes.
There's an old saying that if you hang around in a barber's shop then sooner or later you're going to get a haircut.
If you mingle with people who are willing to peddle hard drugs alongside cannabis then it doesn't take much imagination to work out what might happen next.
It is for this reason that I believe it's time to legalise marijuana.
Before I go any further let me make one thing very clear. I am not advocating the consumption of cannabis. I believe marijuana is a harmful drug in its own right and I have seen first hand the misery it can cause.
When you use cannabis in an addictive way it shuts down your life. You become lethargic and over time you cease to function as a normal human being.
A typical cannabis addict will sit on a sofa all day in scruffy jeans and a T-shirt while spouting about all the plans they've got for the future. A year later they'll be sat on the same sofa in the same T-shirt and nothing has changed.
Cannabis robs people of their ability to hold down a job, it screws up their ability to have meaningful relationships, and its long-term abuse can result in severe paranoia.
It's a drug that is best avoided, especially if you have an addictive nature. The dilemma we face is that simply banning it and pretending it doesn't exist won't work.
Instead it would be better to adopt a system more akin to the one that's already in place in Colorado, where cannabis has been legal to sell under controlled conditions since January 1st of this year.
The Prohibition of alcohol in USA during the 1920s proved that tackling addiction issues by banning the supply of something only aggravates the situation by bringing organized crime into the picture.
Depressingly, in the UK even outlawing a hard drug such as heroin has failed to stop an explosion in its usage. In 1956 (when heroin was made illegal in Britain), there were 317 registered addicts of 'manufactured drugs' in the UK.
If you go onto the National Treatment Agency / NHS websites today, you'll see that there are 298,752 'opiate/crack users' in the UK.* In the 50 years since we decided to tackle drug addiction via the criminal justice system, the problem has increased in size almost 1000 times! Clearly something isn't working.
The causes of addiction are deep rooted. In my opinion addicts are born with a pre-disposition to become over-sensitive to emotional distress. This can be aggravated by childhood trauma and can result in the brain's limbic system having a heightened reaction to stress and emotional pain.
Drugs obviously have addictive properties, but these in the main cause physical dependency - they don't necessarily cause long-term addiction on an emotional level (which I consider to be true addiction) unless other factors come into play.
During the Vietnam War, large numbers of American GIs regularly used heroin. When they returned to the USA the vast majority of them stopped. But around 10 per cent - roughly the same proportion of the population that I estimate suffer from an addictive nature - continued to take it.
I believe addicts are people who suffer from a medical condition that triggers their substance abuse, and this process often occurs at a sub-conscious level.
We must treat them as human beings, not criminals.
If somebody suffers from obesity due to an addiction to sugar (which ironically I consider to be the most addictive substance of all), we rightly treat them with care and compassion via the NHS.
Yet drug addicts are demonized and shunned - even though they suffer from the same emotional trauma that makes others consume excessive amounts of sugar.
This means that we may need to think the unthinkable. Maybe the legalisation of cannabis needs to be just the beginning of a whole new approach that takes a more liberal stance on all forms of substance abuse.
What we require is a fresh start led by government involving inter-agency cooperation from the medical profession and the judicial system.
Unfortunately, because this needs a government brave enough to invest huge resources on helping addicts, it may be a long time coming. I fear that in the meantime society will continue to simply muddle its way through.
The way that addicts are currently treated represents a fundamental abdication of government's responsibility to protect the welfare of a huge part of the population.
• David Smallwood is author of Who Says I'm An Addict?, published by Hay House at £12.99. He previously worked as treatment manager at the Priory Hospital in North London and he is currently director of treatment at One40 in Harley Street.
*NHS data source: http://www.nta.nhs.uk/facts.aspx