Parenting advice symptoms and conditions

My 4 yr old daughter has been on Singulair for 3 weeks and one day as prescribed by an ENT for her persistent sinus problems. I made the mistake of being too trusting and not reading enough about the medication before giving it to her every night for the last 3 weeks. She has been out of control. I blamed it on her oppositional personality but yesterday at my whits end, sat down at the computer to find some parenting advice to work with her temper, aggression, crying, whining etc. - Not to mention nightmares almost every night. When I made the connection to her behavior changes and when she started taking Singulair i found more info than I could imagine. She will never take this again nor will either of my other children or myself! I can't believe a drug with this severe of side effects is prescribed so freely and without any caution from the docs. I blame my self and hope there are not any long term effects from this useless medication.