Isolated urticaria in the emergency department is widely treated by physicians with histamine blocking agents such as diphenhydramine, cetirizine, and cimetidine. Doxepin is a tricyclic antidepressant that has been shown to have much higher concentrations of histamine blocking activity and therefore may be useful in treating urticaria. The purpose of this study is to compare the effectiveness of using doxepin verses a traditional medication, diphenhydramine (Benadryl), in the treatment of isolated urticaria in the emergency department.