Displaying 9 results of Diphenhydramine Impurities Diphenhydramine is an antihistamine medication often used to relieve allergy symptoms, insomnia, and motion sickness. Impurities in diphenhydramine can include residual solvents, degradation products, and other contaminants that may affect the drug's safety, efficacy, and stability. Manufacturers and regulatory agencies monitor and control impurities to ensure the quality and purity of diphenhydramine for patient use.