One brother seemed to need weed to function daily. He struggled at school, never got a real job, and smoked weed every waking hour. He was hitting the bong first thing in the morning. I think he eventually got bored with weed and started using other drugs including prescription pain killers. He became paranoid and psychotic and eventually started pointing guns at police officers. He is now dead sadly, and I wonder every day if I could have intervened in a meaningful way to prevent this.
The other brother is smart. Engineer smart. He designs his own motorcycle racing mods, built an e-commerce site for a Harley Davidson dealership which eventually took over as the principal money earner for the business (until Harley cracked down on 3rd party sellers). When he smoked weed it seemed to quiet his mind and even inspire him - he could work for an inhuman number hours once properly loaded with THC. His boss new he was a regular user and tipped him whenever a random drug test was in the works. Then one day, my brother deliberately failed the test. At that point he seemed to have a mental breakdown and his life has been in a downward spiral ever since. He lives in a school bus with all the seats removed (no other mods). He struggles with poverty.
My general attitude is that THC should be legal, but it is not as harmless as advertised. Occasional recreational use seems fine, but some people who use it to self-medicate may eventually have a reckoning. I still say THC is less harmful than alcohol.