Save. Colace is a stool softener used to treat temporary constipation, making it easier to pass hard stools. Unlike stimulant laxatives, it promotes easier bowel movements by making stools softer, reducing strain and rectal pain associated with constipation. It does not stimulate the gastrointestinal tract.unction. Colace relieves constipation by mixing liquid with the stool, making it softer. When Colace is ingested, it absorbs water from the large intestine and then mixes the water with the stool.