Vyvanse - side effect or metabolic issue? | ADHD Information

Doctor doesn't know what's going on - need any and all similar experiences/opinions.

My 8 year old son (ADHD combined type) has been on Vyvanse (was 50mg, now down to 40mg, 30mg is ineffective) since Nov. He did not react well to the ritalin/concerta meds but has had great improvements both at home and in school on vyvanse.

He has gotten the occasional headache or sometimes tummy ache, but what is really causing us concern is that he is now getting these intense side-effect episodes - not every day however - and they are unpredictable in a somewhat predictable fashion.

He takes his meds at 7-7:30 each morning. most days all is fine - no side effects - good focus, etc . .. Other days, his teacher says around 10:30-11am (always the same time) he starts complaining of nausea, dizziness and headaches. by 11 am, when i end up picking him up, he can hardly sit up - can hardly talk and is so dizzy he has a hard time walking home with me. He comes home feeling very ill and is completely non-communicative until about 1 pm when he starts 'coming round'. he's almost zombie-like for those few hours. by 2pm, he's his normal self again and anxious to go back to school (usually too late for that).

the only thing consistent about these episodes is that they are inconsistent. they occur at the same time of day and are almost identical symptomatically, but they don't happen every day - sometimes once a week (last week 3 times) and some weeks not at all.

He's happy and likes school. Teacher can't see a correlation between these symptoms and any one specific activity.

Can this be a metabolic issue? Perhaps he's metabolizing the meds improperly? What about food sensitivities and the gut? compromised gut=compromised metabolism? can't seem to find too much info on this.

Has anyone else had these intense symptomatic episodes? if so, what have their doctors said about them? are they common? certainly our very experienced doc is not familiar with them.

 As my son is considered hard to treat (we have been through most other options which have not worked for us) we want to make vyvanse work, but this is too high a price to pay.

Any and all suggestions/ideas would be appreciate. Thank you . . .
Is there a snack or meal he is eating on those days and not on others?

Or something to do with the time release mechanism perhaps?  Have all batches of Vyvanse done this or just one particular bottle?

Audrey