Colace is a laxative prescribed to treat occasional constipation, as well as constipation associated with certain medical conditions. Docusate sodium, the active ingredient in Colace, works by allowing water and fats to get into the stool. This helps soften the stool and makes the passing stool more comfortable. Your doctor may recommend stool softeners such as docusate sodium as the first method used for preventing and treating constipation.