Even if it hasn't been fully proven what about the drug induced chemical imbalances that normal people feel on an every day basis and how that effects the day to day lives of the individual?
Examples:
coffee (caffeine can change behavioral processes of the human ingesting)
nicotine (is in direct effect to the glutamate receptor in the brain changing mood)

MSG monosodium glutamate (can cause mood swings from an excessive amount of the amino acid glutamate.

I am someone who is super sensitive to MSG and it pushes me to an ADHD state where my ability to finish tasks is changed if consumed. effects occur about 8 hours after ingestion.