I think it is true that it is under-researched. Current clinical research on psychedelics exclude people who are previously diagnosed and/or have a family history of personality disorders, psychosis and bipolar depression. They also control for set and setting. Under those conditions, it seems that the use of psychedelics is very safe, but it doesn't give us a good idea of the risk of recreational use in the general public.

One interesting recent study I've found is this, but it's too small to conclude anything, and it also does not appear to be peer-reviewed yet: https://osf.io/preprints/psyarxiv/yzmcj