There are many causes of mental disorders. Your genes and family history may play a role. Your life experiences, such as stress or a history of abuse, may also matter.
Biological factors can also be part of the cause. A traumatic brain injury can lead to a mental disorder. A mother's exposure to viruses or toxic chemicals while pregnant may play a part. Other factors may increase your risk, such as use of illegal drugs or having a serious medical condition like cancer. Medications and counseling can help many mental disorders. (from the website https://medlineplus.gov/mentaldisorders.html)