I'm sure this will sound silly or naive. I have a condition in which occasionally I need a painkiller. I have a prescription for it. My question is whether customs will permit it, or should I just get an over the counter pain killer while I am there?

I'm not an ex-pat, just a traveler who will be in country for about three weeks this summer.

Thanks

OTC here you can only get NSAIDs, paracetemol (tylenol) and tramadol. If you require percocet or something like it, better to bring with you but you must get an import permit first. Once you have it, you may legally bring in up to a 30 day supply.

See http://permitfortraveler.fda.moph.go.th/Upload/guidance-for-travelers-to-thailand-version-2.1.pdf

Bring it with your prescription letter, there is mostly no problem with personal use meds less than 30 days, my suggestion is to keep them in your luggage, make prescription copy keep one with you, another with meds.

The worse scenario, the custom will trash it.