Although antihistamines can be harmful with stimulants (it's something a doctor must determine if it's ok) you CAN give allergy meds like allegra or other preventative meds. They don't raise heart rate and my pharmacist said there is no way they can conflict.
Don't give nose sprays either without checking. They contain the same active ingredient as the pills. Big no-no.
It's the season for allergies but you should get him in for the "scratch" test (where he gets the pinpricks with different allergens) to see what could be causing it. With some allergens they can build a tolerance with occasional injections of minute amounts.
Also check with your doctor about amounts. If your son isn't showing agitation or physical problems within a half hour of taking the meds most likely it's not a problem. Strattera isn't a stim so it doesn't show the same effects. Concerta would show as a rash if allergic or agitation if too much (or sometimes drowsy but so can stratterra in regular doses). Do check with MD.
Best wishes to you both. I hate allergies too.
I have been on this post before but things were going pretty well. But, now I have a new question. My little guy, age 6, is diagnosed with ADHD. He is currently taking 40 mg of Strattera, 18 mg of concerta. NOW, he is having a terrible bout with allergies. He has never had this before and now we have to give him some kind of medication so he can breathe better. We are currently giving him breathing treatments but I am not sure it's the right thing or the best. I also am getting worried about the amount of meds he is ingesting. Any advice would be helpful. Thanks.