Well it would be unusual to just use Cardamom, it would be best in a formula. A simple formula could be Cardamom (1 part), Ceylon Cinnamon (1 part), Coriander (1/2 part), Fenugreek (1 part), Holy Basil (1 part). This would be ground up to a powder (I do not know if a Ninja will work, it might, a mortar and pestle is tedious and not very effective). The Chai-like tea would be used at 1/2 tsp per 8 oz hot water, let steep 15 minutes, strain and drink, 4 oz three times per day. BUT your brother needs to carefully monitor his blood sugar levels, this could reduce his glucose level and alter his need for medication. This is imperative to keep track of, as it could possibly cause low blood sugar.