My CAH son has never used it but my 11 year old non-CAH daughter has and is allergic to it.  She gets severe nose bleeds from it.  It is know to have that side affect in some so just be aware of that.

My 9 yr old SWCAH son does suffer at time from headaches but I start by giving him juice or a piece of candy or fruit to see if it is low blood sugar.  Usually it is and there is no need to do anything else as he is feeling fine shortly thereafter.  Have you tried this approach to see if it could be low blood sugar? 

My daughter also suffered from headaches for quite a long time.  We discussed it many times with the pedi, they checked her eyes and we logged what she was eating to see if it was food related.  Finally around the age of 7 I took her to an eye specialist and low and behold she had a vision problem.  One that the pedi would not pick up on.  She had no dept perception and couldn’t see in 3D.  That compiled with the change in the print size of the school books around that age was the cause of her headaches.  She now wears glasses just in school or for the computer.  To this day even with her glasses she can not watch anything in 3D.  It’s like look at clouds for her.