You can't overdose on LSD; some guys took 1-2 thousand times the normal dosage, and it sent them into a comatose state for a day or so, but they were fine.
It's one of the best drugs, very little harm / damage.
Downside, the flashbacks might happen days, months, years later; you could, for example, be having an important job interview, and start tripping out. Or be driving, or something. *shrug*