Can benadryl (diphenhydramine) lower blood pressure?

Yes and Yes: Diphenhydramine (benadryl) can have a sedative and blood pressure lowering effect. While it is not a treatment for patients with high blood pressure, it has a potential side effect of lowering blood pressure.

NO : Benadryl (diphenhydramine) is an antihistaminic drug. These do not affect bp. However, they do relax a person, and relaxation can lower bp, especially if you were agitated or stressed out and now feel relaxed.

It's sedating: Benadryl (diphenhydramine) is a sedating anti-histamine. It can make us a drowsy and therefore more relaxed. For allergies or nasal congestion and you want something less sedating, zyrtec, Claritin or Allegra are available over-the-counter.