Some recommend a minimum of 6 GM/day. I just take a little along with my glucosamine/chondroitin mix (joints). I've taken up to 8 to 10 gm a day in the past w/ no problems.
Some will use higher doses for allergy symptoms. I know a doc who uses it IV for many conditions, things he used to use IV DMSO for (pain states, fibromyalgia , etc).