UKIP policy for drug legislation is to have a Royal Commission to take an unbiased look at the evidence - this seems like a good policy to me - review and follow the evidence to give us the best outcome possible.
Having said that I took a look at cannabis and opium - I chose to look at these as it would seem reasonable for people to 'grow their own' if they were legal... But I ended looking at opium (opiates) in most detail - opium, morphine, heroin.
The big surprise to me was that it is commonly known that, in themselves, they are not harmful substances, pure morphine and heroin do no damage to the human body beyond the potential for constipation(!), as a 'natural product' raw opium is not such a pure substance so is harder to so specific about.
The nasty medical state associated with 'addicts' is universally considered to be a result of their own poor hygiene and contaminated supplies - not the opiates themselves.
The other issue is 'addiction' - a person having any dependency is seen by some as a cause for concern of itself.
A typical addict in the UK will aparantly spend all their free time securing their next 'hit', so as to avoid going through withdrawal. This accounts for people who become addicts finding that their lives fall apart - everything comes second to getting the next hit, they have to put their jobs, families and everything to one side to seek out a supply of their drug - and as their lives fall apart, it becomes harder for them to finance their addiction - having to pay whatever the illegal suppliers demand - without a job, they are often reduced to stealing from their families and from strangers.
I have to say - having looked through all of this, it seems to me that the 'problems' associated with opiate addiction are a direct result of the legislation banning them - nothing to do with the drugs/chemicals themselves. I am still looking at evidence, research - but so far it seems pretty solid that it is the legal ban that causes the suffering and pain, not the substances.
If this is the case for opiates, one has to wonder what researching other illegal drugs would turn up