Pharmacy Reference in Spanish
I tripped on what is like the Physician's Desktop Reference in English today but in Spanish. What I found was from Columbia but it seems to cover typical stuff here. Of particular interest is the ability to look up an ingredient and see what uses it.
Without further ado, see Diccionario de Especialades Farmaceuticas. Armed with decent Spanish knowledge or some translation software, you can do a bit of research on what is really in that stuff the pharmacist gave you and what it will do to you.