To answer your direct question--SXM does not even HAVE a visible customs inspection when you either enter or leave SXM, if you are flying an American carrier. Never flown a South American carrier or KLM, etc. from Europe, although I understand they DO have more strict customs inspections for those planes.
Most likely, if you were to have any problems, it would be boarding the plane in the US (or Canada? not sure where you're from), and coming back into the states. I've been flying into and out of SXM for over 20 years now and have never had someone question my meds. Generally I put them all in one pill bottle. However, I am not taking any schedule I or II controlled drugs, at least not on a regular basis. If I was taking a controlled drug, I would bring the bottle, yes. And if you think you may need a refill while on island. If you are taking a LOT of meds, you might want to see if your pharmacist could give you a list with all the meds that are prescribed for you, in case there might be a question.
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