Other than from companies selling them, info is hard to come by. Unbiased and research-based info is even rarer. So just wanted to share several links that I have found useful.
I don't want magnesium stearate, a commonly used "flow agent", in any of my herbal remedies. It's just one more thing that your body has to work hard to get rid of. "Magnesium stearate is essentially a chalk-like substance, which prevents the supplements from sticking together and allows the machinery to run smoother and faster, which equates to cost savings during the manufacturing process. Magnesium stearate is not a source of magnesium and has no benefits, but may have a detrimental effect on your immune function as stearic acid has been linked to suppression of T cells. The filler also stimulates your gut to form a biofilm, which can prevent proper absorption of nutrients in your digestive tract." articles.mercola.com/sites/articles/archive/2012/06/23/whole-food-supplement-dangers.aspx
Reading the list of ingredients on the lable of your supplements will, sadly, often leave you facing the decision of whether to finish taking the rest of the bottle or tossing it. Please research magnesium stearate. We have enough problems without putting that into our bodies.