Fibralax Plus Sachets is used to treat constipation. It increases the bulk in your stool, an effect that helps to cause movement of the intestines. It also works by increasing the amount of water in the stool, making the stool softer and easier to pass. Fibralax Plus Sachets (Psyllium), one type of bulk-forming laxative, has also been used along with a proper diet to treat high cholesterol.