Like ruby, I used only First Aid to study for the Pharm shelf and I didn't think it was too bad. It makes me wonder though, because the majority of my class walked out of the test like they just attended a funeral. I suppose I'll find out in a week or two.
If you have time and/or are really worried about it, use Lippincott's Pharm in addition to FA to prepare. There were no difficult or tricky questions that I remember on the shelf (all were very doable with minimal studying); the toughest part was recalling ALL those drugs/mechs/side effects.