National Academy of Sciences: Long-Term Consequences of Traumatic Brain Injury.

A few findings:

Sufficient evidence of an association between (among other things):

• Moderate to severe TBI and long-term adverse social-function outcomes, particularly unemployment and diminished social relationships.
• TBI and depression.
• TBI and aggressive behaviors.
• TBI and postconcussion symptoms (such as memory problems, dizziness, and irritability).

Limited but suggestive evidence of a link between (among other things):

• Moderate or severe TBI and psychosis.
• TBI and decreased alcohol and drug use in the 1–3 years after injury.

Also interesting: Evidence is of insufficient quantity, quality, consistency, or statistical power to permit a conclusion regarding the existence of an association between mild TBI and long-term adverse social functioning, including unemployment, diminished
social relationships, and decrease in the ability to live independently.

(Mild TBI is manifested as a brief change in mental status or unconsciousness, whereas severe TBI results in an extended period of unconsciousness or amnesia.)