A mental disease (especially if chronic and untreated) can make people feel that their life is senseless or sometimes desperate.
On the contrary, drugs can never have such an effect. The proof is that you can have the same feelings even in people who never took any drug.
There are also other kinds of disease that can change the feelings an individual has towards himself, the others, or his/her life. For example endocrine diseases, or cancer, or AIDS can give such results.
Then you can clearly see that changes in individual behaviour can be attributed to the fact of suffering of a given disease rather than to the fact of taking a pill of a psychotropic drug.
As a result, if a qualified specialist prescribed you a psychotropic drug for any reason, my suggestion is to take it in the prescribed dose with no fear of brain damage or brain change. There is no risk of it.