Antihistamines are used to treat allergies. Benadryl is one of the strongest antihistamines you can buy over the counter without a subscription. It is stronger than many of the prescription antihistamiens. Benadryl is a common antihistamine. Also, you can drink caffeine soda, tea, of coffee to help if you don't have medicine. Caffeine is a natural antihistamine. Vitamin c is also a natural antihistamine.