Is benadryl (diphenhydramine) safe to take for allergies if you have hypertension?

Yes: Antihistamines don't have any significant effect on blood pressure. Decongestants, however, do - if you want to take anything containing pseudoephedrine, you should first discuss it with your primary care physician.

Yes: It's mostly the 'd' decongestant things that affect blood pressure. Allegra and zyrtec (even the generic) last longer and usually have fewer side effects than benadryl, (diphenhydramine) just dont use the 'd' versions.