I have not seen evidence for changes in brain chemistry, but I have seen that there was evidence for structural changes or increases in the neuronal growth and increase in dendrites, which forms connections between neurons. The area that shows most active growth so far has been in the hippocampal area. Now, since the brain is an organ, one might suspect that structural changes would lead to biochemical changes. The changes created by medication are believed to also occur with psychotherapy, but the changes take longer. However, the changes that occur with psychotherapy last longer than with medication after each has ended.