What is the strongest allergy pollen medicine?

Could you please elaborate on what the most potent allergy pollen medicine currently available on the market is? I'm particularly interested in understanding its active ingredients, its effectiveness in reducing allergy symptoms caused by pollen, any potential side effects, and if it requires a prescription or is available over the counter. Additionally, I'm wondering if there are any other factors I should consider when choosing an allergy pollen medicine, such as cost or patient reviews.