What are symptoms of brain damage from substance abuse?

Depends: This will vary with the substance abuse but usually involves functions of memory, cognition and behavior rather than involving movement disorders (although these may occur later - such as parkinson's). Often mood changes, difficulty with thought patterns, loss of intelligence and reasoning abilities, depression, maladaptation, etc.

Alcohol damage: Heavy drinking results in damage to the cerebral cortex, causing alcohol dementia. Abstract thinking, problem solving, verbal skills, memory, fine and gross motor skills are all effected over time. Personality changes include emotional instability, paranoia, and mood swings.