Will my British hayfever meds work in the US?

Sounds like a stupid question, but I'm on some pretty high-dose hayfever tablets for a grass/pollen allergy, and I'm taking a trip to the States for three weeks - I'm just wondering if anyone knows of any differences in the types of pollen/grass from country to country which might cause me problems? Or is it all the same species/genus etc? (been a long time since I took Biology....)