If this is for employee medical check up, just ignore all the worries because normally they dont check on that field. If they do, probably on Heroin only. However if its a police operasi then trouble comes.
I had a checkup last year for a job application and the story went like:
1) After the check up the nurse called me in regard of a findings in urine.
2) Indeed they spotted drugs particle in the urine.
3) They came up with a form which a checklist of all the drugs we know and ask me to fill any i took within 2 weeks.
4) Trust me i put a lot effort to go round and round on the form trying to find a way to fake the form report.
5) After 15 mins like that i gave her an empty form and the doctor called me in again.
6) He asked me did you took any drugs and i said no. He asked any medication i said yes i took the ubat batuk yesterday and next thing i know, i pass the medical check up.
So i think this is the last resort of excuse to not get caught.