J.P.
Hi--
I have a different take on the situation. Both of my boys and my husband have bad allergies (both food and environmental). Whenever the allergies get out of control they get uncontrollably angry. We have taken an alternative route to treating these allergies. In chinese medicine the liver represents anger. With allergies it is the liver that is most effected. When we calm the allergic response the anger also goes away.
To test my theory you can order quercetin and nettles (google it--you can order both in liquid and capsule form--be careful with the liquid as it will stain everything bright yellow). Give this to him a couple of times a day at first and see if the anger problems subside. This combination is a natural anti-histamine. It works similarly to benadryl, but has no side effects so it will not make him sleepy. Even if it is not an allergy it sounds as if he has a liver imbalance. You can try giving him milk thistle, an herb that will calm his liver. You can also try homeopathic medicine: the typical remedy for the liver is nux vomica.
Just so you have it, other symptoms of allergies include the following: dark and/or puffy circles under the eyes, any type of rash, hyperactivity, frequent constipation and/or diarrhea, stomach aches, sneezing, coughing. If he doesn't have these symptoms try the milk thistle first.
Incidentally, I have recommended this approach to quite a few others, and each time the child's behavior calmed down.
If you have further questions about what I've written here feel free to contact me.
Good luck!