The idea of the chemical imbalance in the brain is off track. We cannot measure the chemicals in the brain. Our neurochemicals change constantly. If we smile, they change, if we frown, they change. We are constantly causing a chemical imbalance in our neurotransmitters. There are medical causes as well. Hypoglycemia, hypothyroidism, allergies, anemia all cause chemical imbalances. The treatment is not a drug but to balance the conditions that are found.