Ask your doctor whether you need the supplement based on your current diet and health. Also ask what benefits and risks the supplement can have, how much to take, and for how long you should take it. Make sure your doctor and pharmacist know exactly which supplements and medicines you're taking.
A "proprietary blend" is a combination of ingredients used exclusively by one supplement manufacturer. No other company produces exact the same combination of ingredients, and, in most cases, it is difficult to know from the label the exact amounts of each of the ingredients in that blend.