Can singulair be taken with zertec: "We offer all the different potencies of tablets, which are to be administered differently. Montelukast can cause different side effects at varying degrees such as gastrointestinal disturbances, hypersensitivity or allergic reactions, sleep disorders, stomach upset, diarrhea, cough, dizziness, headache, nausea, vomiting, heartburn, hives and hoarseness of voice. Singulair is a prescription tablet, approved to help control asthma in adults and to relieve symptoms of unrelenting allergies."