Cannabis is a plant, apart from "hash oil" it is not subjected to any form of chemical extraction or refinement process. As with any plant it contains a mixture of chemicals, several of which may be active. This is why different strains of cannabis from different areas have different effects - some are "laid back" and others are "trippy", it's the same reason different teas and coffees taste different and indeed have different effects. It's also because of this that it isn't strictly correct to call cannabis "a drug", but many would argue that's splitting hairs.
By far the most popular of the illegal substances, cannabis has been used for thousands of years and has never been directly identified as the cause of death, few substances can claim that sort of record. In many respects, cannabis is very safe.
The risk of overdose is nil, it is not toxic nor is it addictive, although as with many things, some people can come to depend on it, but this is psychological and not physical addiction.
Dangers of using Cannabis
By far the main danger of cannabis is the fact that it's illegal. It's a bulky substance and (if you don't want to mix it with tobacco) you need a pipe or other "weapon" to smoke it, these are easy to find if you get searched. A conviction for cannabis possession can damage your career and cause employment problems. For information on legalisation campaign groups check out UKCIA, the UK cannabis internet activists.
Also because of its illegality, hash is sometimes polluted or even mixed with other drugs on occasions.
Some people find its effects unpleasant, it can lead to feelings of paranoia and may make latent mental problems worse, but there is no hard evidence to suggest it causes any real long term harm.
Heavy use can make you lethargic and it can interfere with some kinds of learning and study.
There are claims that the tars in cannabis are carcinogenic - i.e. they cause cancer. Evidence for this is thin, however there are a lot of tars in cannabis.
Prohibitionists point to the supposed increase in strength in recent years with strains such as "skunk" which, they claim, cause psychological problems in users. If this is happening, it's yet another example of the dangers of prohibition which have created the regime for this to happen. There is no doubt though that some forms of Skunk are very strong, if you find the effects unpleasant, don't use it (most people can suss that out for themselves of course).
Being safe when stoned
As with any mood or perception altering substance, it's a good idea not to operate machinery, including driving. Where and when you use cannabis is important, being stoned in the wrong place can be frightening and intimidating.
But it should be emphasised that compared to almost any other substance (legal or otherwise), cannabis is not dangerous.
As with many things, cannabis can become central to your life if you let it and as with many other things, it becomes less effective if you use it constantly.
If you're not use to the effects of cannabis, or if you mix it with alcohol, you run the risk of a "whitey". Basically, when this happens the world starts spinning and you can pass out for a short time. Again, this passes, but its unpleasant and is something to avoid.
Cannabis leads onto other drugs
This is a claim that's been made for many years by those who support its continued prohibition. It is not true, other than in two important aspects:
1: Because it's illegal, some dealers may also sell other substances, hence cannabis users will come into contact with other stuff. This, of course, is (again) because of the law, not because of anything "in" cannabis. Drug warriors claim the "high" experienced with cannabis produces a "craving" for intoxication in the user, which is soon not satisfied anymore by cannabis alone, so they go off in search of ever more potent drugs. This is not true and is another example of drug war hype.
2: Most users smoke cannabis in a mixture of tobacco and it's through this route that many people become seriously addicted to tobacco. This is perhaps the most dangerous aspect of Cannabis and is the one example of cannabis leading on to hard drugs which is true.
Safer smoking
Clearly, not mixing cannabis with tobacco is the first step. There is no need to smoke cannabis in joints mixed with tobacco, although there is a strong tradition of doing this.
Pipes:
The simplest way to smoke pure cannabis, they come in a wide variety of shapes and sizes, grass needs a bigger bowl than hash in general.
Water pipes
Also called bongs, these pass the smoke through water, so cooling it down.
Agent blues/vapourisers
New on the scene these are the way to go. A sample of weed or hash is heated (not burned) so that the active chemicals boil off. The vapour (not smoke remember) then passes down a long channel (a screw thread in an agent blue) before you breath it in.
After a few weeks use, these weapons will become clogged with thick sticky brown tar, this is stuff you would have taken into your lungs if you'd smoked the cannabis in a joint (plus of course all the tar from the tobacco). Scrape it out and throw it away.
Special note on chillums
A chillum is a clay pipe, in which cannabis is smoked along with tobacco. These have to be the worst smoking method because a large amount of smoke goes straight into your lungs
Eating Cannabis
You don't have to smoke cannabis, it can be eaten or even drunk in food.
The thing you have to know is that cannabis isn't water soluble, but it does dissolve in oils. So what you have to do is to powder the hash or grass and heat it in a small amount of cooking oil or butter and then add this to the food mixture. Cakes are the easiest cannabis food to make, simply add the cannabis/oil solution to the cake mix. Make 10 cakes per "teenth" (say 2grms) for starters, see how that goes.
The downside of eating cannabis is that it takes some time to "kick in" - about half an hour to an hour and when it does, well, it can be very strong. Because of prohibition (again!) you really don't know how strong the cannabis is going to be. Cooking can be very efficient, so be warned.