Benadryl etc. (diphenhydramine) is a first generation (H1 blocker) antihistamine. It is used to treat conditions like skin allergies, travel anxiety and motion sickness.
First generation tend to cause more side effects like sleepiness, cognitive impairment, and dizziness than the newer H2 blocker antihistamines like Allegra (fexofenadine) and Zyrtec etc. (cetirizine).
Benadryl etc. (diphenhydramine) is available in capsules and liquids.