My DS is 6 and has been on Strattera for almost a year. We have not had to raise his dosage because it became ineffective, but we did have some insurance issues with the scrip (he takes it twice a day to reduce stomach upset and because it seems to metabolize faster for him and insurance would not cover 4 10mg pills a day which is the only way you can get to 40 in 2 doses). He did have some problems with aggression and irritability, but we have supplemented with a very low dose of Welbutrin and that has helped quite a bit. The stomach irritation was the other main side effect and psychiatrist recommended peanut butter to help with that (which would work better if DS liked peanut butter).