In clinical studies with SINGULAIR 4 mg chewable tablets, the most commonly reported side effects (occurring in at least 1 of 100 patients and less than 1 of 10 paediatric patients treated) thought to be related to SINGULAIR were: • abdominal pain • thirst Additionally, the following side effect was reported in clinical studies with SINGULAIR 10 mg film- coated tablets and 5 mg chewable tablets: • headache These were usually mild and occurred at a greater frequency in patients treated with SINGULAIR than placebo (a pill containing no medication).