Hi, welcome to justanswer, Benadryl can produce urinary retention and painful urination. Benadryl have anticholinergic effects , which can produce inadequate contraction of the bladder muscles and urinary retention. Benadryl (diphenhydramine) is a brand-name, over-the-counter medication that’s classified as an antihistamine. It’s used to help relieve symptoms of hay fever (seasonal allergies), other. Benadryl® (diphenhydramine hydrochloride) Injection, USP. DESCRIPTION. Benadryl (diphenhydramine hydrochloride) is an antihistamine drug having the chemical name 2-(Diphenylmethoxy)-N,N-dimethylethylamine hydrochloride. Allegra (fexofenadine) is effective at reducing symptoms for seasonal allergies and chronic hives without significant drowsiness, unlike Benadryl. Benadryl (Diphenhydramine) is great for allergies, but curl up on the couch after taking it and get ready for a nap. Xyzal (Levocetirizine) is good for treating allergy symptoms, but it can cause drowsiness. Questions & Answers. 1. Can you give a dog Benadryl? Yes! Dogs can take Benadryl, for much the same purposes as humans. On the other hand, the dosage is different for dogs, or even a dog the same size. Long-term Benadryl abuse can cause serious memory loss and even dementia. Benadryl has not been proved to be completely safe for children below 6 years of age. Unless specified by the paediatrician, avoid using Benadryl for children. View Benadryl Allergy Relief - 12 Capsules. Shop online today. Long-term use of anticholinergic drugs like Benadryl, some antidepressants, and others has been linked to increased risk of developing dementia.