Diphenhydramine, which came into commercial use in 1946, is an antihistamine that can be used for insomnia, although it is mainly used to treat allergies. Plus, it is used by mouth, injection into a vein, injection into a muscle, or applied to the skin. Basically, this medication reverses the effects of histamine on capillaries, reducing allergic reaction symptoms. Moreover, Diphenhydramine readily crosses the blood-brain barrier, resulting in drowsiness, and suppressing the medullary cough center. When it comes to the side effects of this medication, they include sleepiness, poor coordination and an upset stomach. Besides, its use is not recommended in young children or the elderly. There is, however, no clear risk of harm when used during pregnancy. On a side note, the use of Diphenhydramine during breastfeeding is not recommended. So, for the safety of your baby, you must stay away from it if you are a nursing mother. Bear in mind that this drug may be taken with or without food. However, you need to take exactly as directed. In other words, do not take more than is recommended.