Does folic acid deficiency cause irreversible nervous system damage?

Not usually, but : Do you really have Folic Acid deficiency? If so, you could have elevation of homocysteine, which could be a risk of heart attack and/or stroke. If this is the case, have your doc check for an mthfr (tt or ct allele genetic condition), as this could be quite a problem if not addressed. The tt is relatively uncommon, but must be treated.