According to the European drug advisory peeps, 60% of the UK adult population admits to having experimented with drugs.
The figures are much the same in the rest of Europe, too.
Most of those 60% do not become addicts; 20% of them try it once or twice and don't bother again, and 40% of them become recreational drug users. They consider drugs to be fun, much like alcohol, an adjunct to parties and artistic endeavours. Of that 40% of recreational users, only 5% of recreational drug users develop "problematic drug use". Most of those have additional social, psychological and educational attainment issues and use drugs like a person with severe illness uses medicine.
Most people smoke weed and drop a few pills during their college years, they grow out of it, and they have no long term ill effects. Taking drugs is a rite-of-passage, and when drugs are used recreationally, by students and art teachers and musicians, then drugs are not a problem for individuals or society, and criminalising such behaviour is counterproductive.
Cannabis is a short-acting, mild hallucinogen, and most people who are deemed to be "addicted" to cannabis are "psychologically addicted" rather than physically addicted. Their problematic cannabis use is a behavioural issue, not a physical issue. They won't die or get sick if they give it up, (like alcoholics and heroin addicts do), they don't feel so bad without it that they go out selling their bodies or they commit crime to fund their drug use, but they might feel... bored, and restless, for a few hours.
Of course, being around pot-smokers when you're not a pot-smoker is... boring. People make no sense, they rant polemics, they create bad art, they seem... sedated. That's because cannabis is a hallucinogen; it makes people seem slightly psychotic. That's what hallucinogens do, in their different strengths. Some people like to feel like that!
There has, in the past ten years, been a lot of consideration given to the possibility that regular cannabis smoking predisposes a person to experiencing psychotic illness. Some scientists suggest that long term, regular use of cannabis may exacerbate psychotic illnesses in people who are predisposed to such, but I personally think these statements are scare tactics, the use of such supposedly to enforce a "no-drugs" mindset.
Of course, drugs and mental illness don't mix; but I do not believe that we can state that drugs cause mental illness -- the causes of mental illness are far more diverse than simply... "oh, he smoked pot, once, when he was 18"...
It does appear that habitual smokers' behaviour, when they've run out of cannabis, changes, and they seem... agitated, and agressive, but this is because while high on cannabis, normal fears and anxieties are muted.
Get used to taking cannabis, for more than 10 days, stop it, suddenly, and when the cannabis levels in the brain drop, those normal fears and anxieties seem magnified. This can make people "stroppy", and aggressive. This behaviour is magnified in young men, who are naturally aggressive anyway, thanks to the testosterone, and leads some parents to become anxious that their children are developing psychosis, but the agressiveness wears off in a day or two and a person will have no long-term side effects.
Cannabis is a drug that, while abused, also has great potential as a healing agent for people with numerous real, physical illnesses. Preparations of cannabis are used to treat.... multiple sclerosis, side effects of chemotherapy, side effects of aids therapies, glaucoma, and... there's a big list. Oils from cannabis are great skin softeners, cannabis (hemp) makes a great organic fibre, etc, etc...
The brain itself actually has cannabinoid receptors. Unlike "opiate receptors", that are used by the body's natural opiate-like neurotransmitters, the body does not actually create it's own cannabinoids, and has to obtain them from outside to stimulate them. Which is interesting, is it not?
Culturally, cannabis is used by many religions and groups as a ... meditation, or spiritual aid. Sufi's, assassins, Siva-worshippers, Rastafarians, Pagans, all have used cannabis, ritually, historically, allegedly, as a way to become... closer to God...
My opinion is, though, that maybe you shouldn't be so ... imposing, on someone you decree is a friend. You can't change other people's behaviour by talking at them. But if you cannot abide their behaviour, and value them as a friend, I think you should be able to say, to a friend... "Look, my friend; when I come to visit, I'd prefer you to be straight/sober/not using?"
If they don't, or can't, or won't, stop visiting. That's all you can do!
