The dosage of cocaine varies greatly since it's so easy to cut; you may have pure shit straight off the key, or you may have nothing but baking soda. Generally the best rule of thumb is to "bump" it first (a bump about the size of a pea on a knife blade/key/bent matchbook) to test the quality, and work your way up to lines. No drug is ever "safe"; cocaine can cause cardiac arrest, stroke, etc. when done without moderation. High-quality cocaine will make your face numb, but since it's a local anesthetic it must be applied directly to the tissue in question for it to work efficiently. I'm not sure if this method works on external tissue, but by applying baking soda to your gums, followed by a dab of coke, it'll numb the Hell out of your mouth...
