In my opinion, Pharm was much more difficult on COMLEX than on USMLE. You really had to have some in depth knowledge of side affects, interactions, etc. Also, Pharm as a subject receives much more emphasis on COMLEX than on USMLE.
To do really well on COMLEX pharm, you should use a source like Lippencott or something similarly detailed. For USMLE, First Aid is fine--or to maximize your score, you could use something like the Kaplan pharm book, which isn't too bad.
For Comlex, you really need to know the psyc. drugs well (neuroleptics, benzos, SSRIs). The USMLE put more emphasis on autonomic drugs (epi, norepi, atropine, etc).