Can i take penicillin if i'm allergic to benadryl (diphenhydramine)?

Yes, assuming . . .: The antihistamine Benadryl (diphenhydramine) is not related to antibiotics, penicillin. So if you're allergic to diphenhydramine, you should still be able to take penicillin, assuming that you're not allergic to penicillin, too. Out of curiosity, what were your allergy symptoms? Perhaps you're allergic to filler & dye in pill, not to diphenhydramine.