MSM is a nutritional substance, not a drug or medication. Please consult your health care provider before taking any supplement with any medication. And there are no additives. When you begin, the general rule of thumb is one 500 mg. You must decide the amount that works best for you.
Every body reacts a little differently.
Below is an example, based on a 150 lb. This may seem like a lot, but you'll quickly see how your body enjoys it. MSM Powder Up to 100 lbs. 101 - 150 lbs. 151 - 200 lbs.