 [ Symptoms ] runny nose took antihistamine developed fever reaction to drug or coldallergy symptom  took over the counter diphenhydramine hci 25 mg no fever prior to taking it but i had a bad runny nose [ Disease ] benadryl diphenhydramine does not cause a fever nor is fever an adverse reaction to this antihistamine allergies do not cause fever so any elevation in temperature that may have experienced is most likely do to your cold assuming you have correctly diagnosed yourself fever is the body is natural response to fighting off an infection