Here is a story of how my girlfriend went to New Mexico for a funeral and suffered the most horrible allergy attacks. Those allergy attacks soon ceased to exist once she took a few antihistamine pills.
She's allergic to dust and certain plants and New Mexico happens to have a lot of dust and the plants that she's allergic too. She wasn't thrilled at the idea of having allergy attacks around her family for 5 days. I told her to buy some Benadryl as soon as she got there and hopefully that would help.
The active ingredient in Benadryl is Diphenhydramine HCI 25 mg which is an antihistamine. She called me in the evening on her 2nd day of being there and told me that she had gotten a box of Benadryl and that it had helped her greatly. She said that it made her a little bit drowsy at first but it eventually wore off and her sneezing and itchy eyes soon stopped. She was so happy to be able to talk without sounding stuffed up and not rubbing her eyes constantly. It apparently works for quite awhile when taking the recommended dose.
She enjoyed the rest of her trip (or as much as you can enjoy a trip for a funeral) because her allergies were under control. She recommends this allergy medicine to anyone with moderate to severe allergies.