Mental illness how do they get that?

usually it is already latent, and may have been worsened by your surroundings e.g. a traumatic event, stressfull home life e.t.c can also be hereditry

There is three ways to "get" mental illness
1. Hereditary - Mental Illness can and usually is passed down from generation to generation. It can skip generations and doesn't always show as the same mental illness it can be any of the diagnosis (Dx)

2. Environmental- Child abuse, rape, trauma etc can cause the brain to "tilt" and a person can become Obsessive Compulsive (OCD) Schizophrenic, etc.
3. Chemical- Certain drugs like PCP and LSD, can cause long term mental illness like Schizophrenia, Babies born addicted to Meth. often are born with ADHD, OCD, Aspergers etc. If a pregnant mother is exposed to dangerous chemicals the effect on the baby can be permanent mental illness as well as physical disabilities.

4. The potential for mental illness "may" also be brought on, and I say "may" in quotes because there is evidence but no conclusive proof (can there ever be conclusive proof given human inadequacy?) that prescription psychiatric drugs may cause irreparable harm if administered to children who have been misdiagnosed or are perfectly healthy. I am familiar with a nearby community with one of the highest per capita incomes in the United States. According to friends of mine who live in that community the peer pressure among parents to drive their children toward academic achievement is enormous. Starting in pre-school, doctors are prescribing Ridilin and other drugs to improve their child's focus and attention span. Because there are few studies regarding the long term effects of these drugs on prepubescents, the possibility that serious mental issues may occur years down the road must be regarded as troubling.