It seems that for food, you only need to restrict the tile the food is at and any animal that restricted would not touch the food no matter what. But for drugs, seems like they get a longer mouth or tongue or something that allow them to take it from a tile over.
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This is intentional behaviour, animals will sometimes try to ingest random things out of curiosity and they will ignore their restrictions when they do so (since they're animals).
Anyways thanks for taking the time! ;)