What phenomenon might occur years after using LSD, causing an individual to experience prior effects of the drug?

The phenomenon of experiencing prior effects of LSD long after its use is known as a flashback. Flashbacks are unexpected and involuntary recurrences of perceptual experiences that were originally induced by the drug. They can happen days, weeks, or even years after the actual use of LSD and can manifest as visual distortions, feelings of disconnection from reality, or other sensory effects that recall the drug's initial high.

While other terms like psychosis, residual effect, and hallucination relate to altered mental states or perceptual experiences, they do not specifically describe the spontaneous and recurring nature of flashbacks associated with hallucinogen use. Psychosis refers to a severe mental disorder characterized by a disconnection from reality, which can be a consequence of prolonged drug use but is not limited to LSD. Residual effects generally refer to lingering effects from a drug that may not completely resolve but do not have the same sudden and transient quality as flashbacks. Hallucination is a broader term that encompasses experiences of seeing, hearing, or feeling things that are not present, which, while related to LSD use, do not capture the specific recurring nature of flashbacks.