Hi, Benadryl contains Diphenhydramine , which is an antihistamine. It blocks the effects of the naturally occurring chemical histamine in the body. Hence, it is used to treat sneezing, runny nose, itching, watery eyes, hives, rashes and other symptoms of allergies. it is also used to suppress coughs, to treat motion sickness and to induce sleep. More frequent side effects caused due to intake of Benadryl include: sedation and thickening of bronchial secretions. You may need to give mucolytic-mucokinetic containing medication if the cough is caused due to thickening of bronchial secretions. Also, taking supportive measures like doing salt water gargling and steam inhalation would also help in easy drainage of mucous. Hope the information provided would be helpful. Let me know if I can assist you further. All the best. Regards, Dr. Ashakiran S