While (Vitamin B) might not be anything to worry about, you might want to look at it this way, "Why would a kid have Folic tablets in his room?"
I hate to assume anything but I could/would imagine that he thought it might be something else of the more "narcotic type".
Folic Acid is primarily taken by women of child-bearing age to help prevent birth defects such as spina bifida. It also helps with the production of cells.
Regards,
J