Lsd is a wonderful drug with lots of promise for use in psychology, before it was made illegal in the 1960s it was helping lots of people psychologist were using it with very good results. Flash back do occur rarely, proper setting and understanding of what Lsd does will help a person deal with difficult repress feelings that need to be refiled in the mind, this is what usually called a bad trip, and may have some flash backs, these repressed memories need to be come conscious and delt with, when they are great improvements of mental and physical health accure.
LSD, Ayahuasca, shrooms, peyote, do not cause brian damage, but alcohol,and crystal meth does. Most of these ethogens give improved mind performance, and help people break addictions to drugs.