BENADRYL® Allergy Relief lasts for up to 8 hours and provides fast-acting allergy relief and treatment of hayfever, dust, pet and skin allergies Acrivastine, which is unique to BENADRYL®, is a fast-acting antihistamine, making it an effective treatment for allergy and hayfever symptoms caused by pollen, dust and pet allergens. BENADRYL® Allergy Relief can be taken up to three times per day as required, so you can take it as and when you need it. Want hayfever medication that gets to work fast? Try BENADRYL® Allergy Relief which starts to work in 15 minutes.