And Bumbaclot, saying cannabis is 'not addictive' is just nonsense. It's not as addictive as nicotine or sugar, say, but it is every bit as addictive as alcohol. If you smoke it like a 'social drinker' - one spliff a night, say - then you'll be fine; but if you smoke it like a park bench drunk - a spliff before breakfast and several throughout the day - then you will develop a problematic addiction.
There are clear, physical, negative effects when a heavy daily cannabis smoker doesn't get a smoke, particularly if they can't manage the effects and withdrawal symptoms because they have 'real life' to live while they are coming down (and the effects are stronger with skunk and with resin/hash that has been cut with other sedatives like largactil). These are the physical effects heavy cannabis users are very likely to experience if they stop:
In the first 24 hours:
Cannabis sedates you, so you need to sleep. If you can't you get ratty.
It makes your blood sugar levels drop, so you need to eat. If you can't, you get very ratty, and can get diabetic-like hypoglycemic symptoms.
It makes your blood pressure drop, so you get all the symptoms of low blood pressure, especially if you can't go and lie down quietly: dizziness, sickness, headaches and anxiety.
It's a dis-inhibitor, so you are more likely to do stupid or dangerous things, and/or to lose your temper and/or be violent.
In 24-72 hrs:
Blood sugar stabilizes quite quickly if people eat, but blood pressure may be erratic, or normal blood pressure may feel like high blood pressure, because you have become used to lower levels. You may continue to feel dizzy, sick, headachey and anxious for a few days.
You will probably experience extreme tiredness, mood swings, erratic behaviour, and possibly anger and aggression.
After about 48-72 hrs:
Your body will start to get rid of toxins, which will take 2-3 days. If you have been smoking a nice mild naturally-grown plant form of cannabis, there won't be many toxins to get rid of. But if you smoke skunk or unpure hash, there could be a lot. You will literally excrete toxins. In most people that will just be a bit of a nasty sweat and perhaps a slightly dodgy tummy. But I have seen a heavy hash user literally sweat brown gunk out of the palms of his hands on days 2, 3 and 4 after giving it up.
Your sleep will be disturbed and erratic: you will wake when you want to sleep, and vice versa.
You will shake, sweat more and feel generally unwell - like you have flu.
And just like an alcoholic, you will remain more 'sensitive' and more likely to start using cannabis again...
The old myth that "cannabis isn't addictive" grew and flourished in the days when people were generally smoking their friend's big brother's home-grown weed - mild, natural stuff consumed at evenings and weekends only. Now that more people are using much, much stronger stuff that is artificially grown and 'chemically enhanced', and they are smoking it more often, side-effects and withdrawal effects are becoming more obvious. So please Bumbaclot, face facts, and stop repeating the myth.