farmacia - look for the green neon crosses. They are everywhere in the centre.
There are two 24 hour pharmacies, one by the Duomo and another in the railway station.
Medicines are dispensed immediately when the pharmacist is handed the prescription.
acetominophen in Europe is called paracetamol.
some drugs, like antibiotics are very cheap compared to the US (e.g. €7 for Augmentin (12xtabs)), or €7 for a month of birth control
some are very expensive (e.g. €3 for 10 x tylenol or ibuprofen).