06/02/2012 18:47 GMT | Updated 07/04/2012 06:12 BST

Can Cannabis Drive You Crazy?

A growing number of people say that cannabis should be legalised and there are many compelling arguments for this: cannabis can help the elderly and infirm dull their pain, taxing it would divert profits from the mafia to the state and many say that tobacco and alcohol are worse.

In January, Richard Branson told a Parliamentary Select Committee that cannabis should be "regulated and taxed" and the Guardian tells us that "people who buy drugs to share with friends could avoid prison under guidance that also recognises medical use of cannabis."

All this sounds very progressive and perhaps Branson is right when he says decriminalisation would be a "win win all round" scenario for a state which, he says, spends £200million a year on policing low level drug crime.

But can someone please explain the logic of decriminalising the possession of a substance which is illegal to supply? If I'm allowed to smoke dope does that mean the law turns a blind eye when I do a transaction with my supplier?

When I was a student I thought cannabis was a harmless pastime, no worse than alcohol, and I was encouraged by the fact that it's not addictive.

Many years later I ended up working for an addiction rehab clinic in Scotland where I found out that not only is cannabis addictive but the skunk version of the drug is known to send as many as 20% of users into a psychotic state. In other words, it can drive you mad. And everyone knows that the THC content of street cannabis has been going up for years.

Dr Margaret McCann, the medical director of the rehab clinic where I work, told me "There are increasingly potent strains of cannabis, such as skunk, which can cause psychotic illness. Many of the patients at Castle Craig are being treated for cannabis addiction, where cannabis is the primary drug of the addiction."

This information shattered my belief that cannabis is harmless and considering I was living in ignorance of the facts, I wonder if Sir Richard and his chums on the Global Commission on Drug Policy have been fully informed of the risks involved.

They should talk to Sue Philips from Newcastle as she was addicted to almost every drug available, as well as the methadone peddled by the NHS, for over 30 years. Social services considered her a lost cause but eight months of abstinence-based addiction treatment got her onto the straight and narrow.

This is what Sue told me about dope:

"I was a heavy cannabis user for 32 years - I would smoke a joint before I'd get out of bed - and I can remember phases of extreme paranoia. I'd have all the curtains shut and if I heard footsteps outside they'd be coming to my door. Now I know that cannabis is the leading cause of drug-induced psychosis (psychosis is when you think that things happening around you are real, and they are real to you, but not to other people).

"A lot of people don't know that cannabis is a mild hallucinogenic, and its THC content is getting stronger and stronger. If you keep putting hallucinogenics into your system your perception of reality is going to be hugely changed. I know several people who have ended up being diagnosed for schizophrenia through cannabis use. It's not a safe drug, it's not a soft option."

I suggest that anyone promoting the advantages of cannabis should speak to a therapist or psychiatrist who deals with addicts on a regular basis. Or go to a NA (Narcotics Anonymous) meeting and see what they think.