Montelukast
"Started taking Singulair with Zyrtec 3 weeks ago for a severe allergy I developed to my 3 pet rabbits. No side effects to speak of (I did have a headache one day, but I don't think it's related) and today I held one of my bunnies for the first time in 6 months without allergy symptoms. Now I don't have to get rid of some beloved family members!"