Pot doesn't make people crazy. Crazy people gravitate toward pot.
Almost 80% of people with manic depression have an alcohol or drug addiction. My neurologist cited the study, and I will see if I can't hunt it down.
When you suffer from mental illness, you will do anything to make the demon monkeys in your head calm down. Pot is the most therapeutic drug I have ever found for dealing with mania. Mania occurs when you your emotional sinwave spikes through the roof elevating heart rate, sex drive, and energy by dumping massive amounts of Serotonin, Norepinephrine and Dopamine into the neural synapse. This can cause a person to become unable to sleep for days on ends. After day three a person could become delusional with signs of psychosis. This is completely natural with, and usually takes some sort of powerful tranquilizer with mood stabilizer to bring the person back down to a reasonable level.