Robin Williams -- Parkinson's a Factor in Suicide ... But NOT the Cause

Robin Williams' Parkinson's diagnosis had an impact on his depressed state ... on both a psychological and physiological level -- but it's NOT why he committed suicide ... multiple sources connected to the family tell TMZ.

We're told ... Robin was struggling emotionally with the diagnosis ... like anyone would. Our sources say Parkinson's was NOT the reason for his depression ... something Robin lived with for years. But we're told the Parkinson's news "exacerbated" his depressed state of mind.

We're also told doctors were treating Robin with meds to slow the progression of the disease down, and the cocktail -- which was a work in progress to get right -- also had a negative impact on his emotional state.

And doctors believe Parkinson's itself physiologically triggers depression in people.

But our sources make it clear ... the diagnosis of Parkinson's did NOT trigger Robin's suicide. It was the result of chronic, intense depression that dogged the actor for much of his life.