They are recurrences of images or effects that were experienced during a previous LSD administration and they can vary in intensity and duration. These flashbacks can last from a few seconds to several hours. This discussion of flashbacks highly exaggerates their dangers. Flashbacks seldom occur to those who have taken LSD under properly conducted conditions, and when they do, they may be used fruitfully as part of the learning process. Most difficulties reported are the result of uninformed, illicit use.
Flashbacks result from the individual, particular psychic structure of the imbibing person.
Again, the aid of a truly informed therapist can be of great help in resolving problems resulting from flashbacks. . . . . . . . . . . For those who wish to understand the true nature and potential of psychedelic substances, there are many excellent books available, as well as hundreds of published papers.