hello thank you for trusting HCM Dear antihistamines have been successfully used for years in the treatment of seasonal/persistent allergic rhinitis. The new generation antihistaminics are all safe, with negligible sedative effects, excellent tolerability and have no influence on cardiac parameters. Montelukast when used as monotherapy is efficacious and improves quality of life. Combination therapy (montelukast plus levocetirizine) is a more effective strategy than monotherapy in the treatment of persistent allergic rhinitis. most common side effects like drowsiness, fatigue,weakness,tired feeling,stuffy nose,sinus pain,sore throat,cough,vomiting,diarrhea, etc. avoid cool drinks and freeze water, avoid allergen. you can use montelukast along with levocetrizine.attend allergy clinics,if symptoms not improved please consult your doctor he will examine and treat you accordingly. I think I answered to your question if you have more questions feel free to ask. take care