Diphenhydramine is an antihistamine mainly used to treat allergies. It can also be used for insomnia, symptoms of the common cold, tremor in parkinsonism, and nausea. Diphenhydramine Hydrochloride Crystalline Powder is an antihistamine medication used to treat allergies, motion sickness, and insomnia. It is also used as a sedative and to relieve symptoms of Parkinson's disease. The powder form allows for easy administration and dosing. It is commonly found in over-the-counter sleep aids and allergy medications. Diphenhydramine Hydrochloride Crystalline Powder is a versatile medication with a wide range of applications.