I am neither an M D nor a health care provider but I would like to share with you my experience with Benadryl causing severe hypertension in myself. I am a 43 year old female with high blood pressure. I have been taking Enalipril/HCTZ for the past seven years with great results. This past spring I suddenly developed allergies to grass, mold, and pet dander. My primary doctor told me to treat this with OTC Benadryl. For a while it seemed to be working well. After about a month the effect was not as good. Without my doctors knowledge I increased the dosage until I got the desired effect. After a week or so I began to experience heart palpitations, tremors in my hands, and blurred vision. I immediately went to see my doctor. My blood pressure was taken and was 180/102. My doctor told me to stop taking the Benadryl and find a different antihistamine. Nothing worked nearly as well as the Benadryl, so I began taking it again. This time on the recommended dose I started having the same symptons as before. I had my BP checked and once again it was high. Although not as high as it had been before, it was 164/90.  needless to say I immediately stopped taking it and just put up with my allergies for the rest of the season. My BP is back to normal, being controlled with my medication.