BENADRYL DOSE:: Up to 50 mg each dose every 4 hours as needed. Maximum dose not more than 400 mg in a day. Adverse events: drowsiness, hypotension, increased heart rate, paradoxical excitement, dry mouth, thickened bronchial secretions, etc. ...Read more.ou are not alone. 50 million people in the United States suffer from allergy symptoms and its prevalence is increasing, affecting as many as 30 percent of adults and up to 40 percent of children. Allergies can be frustrating and can be an annoyance if not properly treated.