Long Term Effects

Long-term effects appear after repeated use over a lengthy period, or some time
after the short-term effects of a single dose have worn off. "Flashbacks" (unpredictable, spontaneous recurrences of the original LSD experience without the user's taking the drug again) can occur weeks, months, or even up to a year after the last encounter with the drug. Typically, flashbacks last only a few minutes or less and are usually visual images ranging from formless colours to frightening hallucinations. The cause of the flashbacks is unknown, but they frequently occur after an LSD user smokes cannabis.

Chronic LSD use may result in prolonged depression and anxiety.

LSD & Pregnancy

There appears to be a higher risk of spontaneous abortion and congenital abnormalities in babies born to women who regularly used LSD during pregnancy.
But in almost all such cases reviewed, the mothers had also taken other drugs during pregnancy; it is thus difficult to determine how much each drug contributed to the problems.

Studies associating LSD use with chromosome damage have yet to be confirmed.