Step 1: Do the freakin reaserch!
basically you need to find out which is which, what is what, and what you need
PERSON: hello my fine shop owner, I would like to purchase provisions for my escapade to another country. i happen to have a light headache, what types of pain killers do you have?
MY FINE SHOP OWNER: we have methadone hydrochloride, Paracetamol, and of course Oxycodone
of course i bet if you haven't done your research you would no be able to tell which of these medicine is which
methadone hydrochloride: is a pain killer that not only stops pain, but it can also stop your lungs or slow them enough to suffocate you to death
Oxycodone: an effective pain killer... so effective it is also a very powerful narcotic
Paracetamol: a mild pain killer, while ineffective with inflammation, it will get rid of that headache quickly
so remember the almighty rule for escapes
find out which is which, what is what, and what you need
note: i have no idea why Oxycodone or methadone hydrochloride would be sold in a store, but you can never be too sure