I was wondering the same thing. I was thinking the gluten might be in the protein structure of the growing plant, but you're saying it is only in the grain(seed)?

This is from PersonalMD.com: "If I'm allergic to wheat, will I have a reaction to wheatgrass?
Answer: It's very unlikely that if you are allergic to wheat, that you will have a reaction to wheatgrass. Wheat allergies are usually a reaction to the gluten found in the wheat berry. Wheatgrass is a vegetable, cut before the wheat plant forms the grain and the gluten found in the wheat berry. Therefore, wheatgrass contains no gluten."
>>>>>>>>>>>>>
Some people are allergic to the gluten portion, some people are allergic to wheat, but not gluten. Some people are allergic to both gluten and wheat.

I would not used a commercial product containing wheatgrass. You don't know how careful they were in processing. Some of the wheat berries could get into a commercial product. Beyond that, if you are growing and juicing your own, you can control how careful your quality control is. If you still react, don't go there again. But if you don't react, proceed with caution and don't start drinking tons of it.