What causes LSD flashbacks?
No one really knows, since there has not been a lot of LSD research performed over the past 20 years. It is clear that flashbacks (hallucinations occurring months or years after the drug has been used) are not caused by LSD that is still in the body. Flashbacks probably occur because of psychological “triggering” (such as an emotional bad memory), due to cues in the environment. However, this is simply speculation, since research on flashbacks is inconclusive.