It is better to be cautious about doing it no longer than 3-4 minutes at a time. The oil triggers the release of salivary enzymes that draw toxins and bacteria/yeast out of the protective lining of mouth, throat, chest, stomach, and clean the blood in the head area. This happens very quickly. By holding the oil in the mouth for 20 minutes you may be reabsorbing these noxious susbtances. If you want to do it longer than 3-4 minutes, you may use new oil.