Side effects of ascoril in 6month old baby?

Not recommended. Firstly, a 6 month old is too young to take any OTC meds except maybe tylenol (acetaminophen) and/or motrin. I don't think ascoril (dextromethorphan) is even indicated for children less than 2 yrs old and even then studies done on 2-6 year olds have shown no benefit and potential for side effects like dizziness, feeling weak and irritable.