Black Draught Laxative - 6 oz. Black Draught Laxative With Casanthranol Black Draught Laxative is used for relief of occasional constipation. Black Draught Laxative has as the main ingredient Casanthranol - 90mg. per tablespoon. Syrup of Black Draught has been family trusted for over 100 years. This product generally produces bowel movements in 6 - 12 hours. Each bottle is six fluid ounces (177 ml).