According to Herbs and Natural Supplements: An Evidence-Based Guide, “Although Slippery Elm has not been scientifically investigated, the FDA has approved it as a safe demulcent substance.”
The product is Slippery Elm Bark Powder. ½ to 2 teaspoons up to 3 times a day. For a thick and mucilaginous jelly, add 80ml water to every ½ teaspoon slippery elm powder (more or less water can be used for the desired consistency). Please note that it can at first appear lumpy and can take between 1 and 5 hours to form. We recommend preparing before bed, leave overnight and use in the morning.