Avoid taking diphenhydramine/Benadryl/Tylenol PM/Advil PM and other over-the-counter sleeping pills containing diphenydramine. Diphenhydramine (brand name Benadryl) is an old antihistamine drug which is used as a sleeping pill because of its side effect of drowsiness. It can cause confusion, anxiety, constipation, fatigue, unsteadiness on your feet, blurry vision and urinary problems, especially in older people.
A Re-Evaluation of Diphenhydramine– Could This Old Drug Be Bad for Our Old? (Massachusetts General Hospital Drug Therapy)