What are the long-term psychological effects of LSD?

No one knows for sure. More research is needed. There is evidence to show that LSD may cause flashbacks months and years after the trip has ended. It may also speed up the onset of medical conditions such as schizophrenia. These effects are usually associated with chronic use.

There are a lot of myths out there about LSD. It does not, for example, cause brain damage. However it is still a potentially dangerous drug.