It's difficult to 'educate' people when we don't know a lot about it. For example, for many people weed is good for a few years, but eventually descend into par

It's difficult to 'educate' people when we don't know a lot about it. For example, for many people weed is good for a few years, but eventually descend into paranoia, unable to smoke even a little bit. What is causing that? A change in the brain? Is that harmful? Are there other side effects?