Modern cannabis has been genetically engineered to be as high in tetrahydrocannabinols (THC, the part that gets you stoned) as possible. Weed and hash from the 60s–90s typically had a THC content of around 4–7%, where as today’s strains (skunk) can easily be 18–21%, with some (probably dishonestly) claiming to be as much as 27%. For those that do not have a tolerance for it that can be like going from sipping a pint of cider to necking a bottle of vodka.
On top of the active content there are two different types of strains with specific attributes. The sativa can be good for creativity, chattiness, mild euphoria and physical activity. The other type (broadly speaking) is the indica, which has a much more physical effect. It gets called ‘couch lock’ as it can lay you out on the sofa and effectively end your day. Those who prefer this type often smoke/eat/whatever in the evening to give them a decent night’s sleep. There are also hybrid strains, typically 60% indica/40% sativa or vice versa whereby growers try to bring out the qualities of both strains in one plant.
As a kid growing up in London we smoked hash and Thai grass, which was pretty mild. I had two friends who smoked it a lot and it was terrible for them. One is in assisted living accommodation and the other killed himself aged 16. Before anyone starts blaming the weed for this I don’t think it was a causal factor – both were diagnosed with schizophrenia and it seems likely that their condition was made a lot worse or accelerated by their constant smoking, but it didn’t cause it. They would be schizophrenic whether they smoked or not.
I also had a friend who had a psychotic episode in his 20s as a direct result of getting stoned. It was really frightening. He thought his girlfriend was a vampire who was trying to kill him. If you’re prone to these mental health conditions when you are an adolescent then regular smoking weed can be really bad for you – your brain chemistry and emotional maturity can be badly affected by it. At the same time smoking lots at that age can distract you from your emotional/psychological problems and you can get locked in loop. It can feel like it’s helping you while at the same time doing a lot of damage. Although my experience is of course anecdotal that’s what happened to my two friends.
Despite this I think it should be legal, heavily taxed and properly restricted to those who are old enough to smoke it. Sure some people will still get messed up by it of course, just as some people can’t drink without becoming nasty, abusive and violent arseoholics. That’s just people. The way the world is going I think it’ll be legal here in maybe 10 years or so, so it’s important to get educated.
Statistically I don't think smoking weed has ever been cited as a cause of death in and of itself. Ironically the people who get killed are dealers trying to protect their market or those who move it on in quantity – an ounce/ 28g of skunk can sell for as much as £220 or more in the UK, so obviously there's a lot of criminality involved in selling it.