What do cathartics primarily do?

Cathartics are primarily used to stimulate bowel movements and facilitate the evacuation of substances from the bowels. This action is crucial for treating conditions that require the removal of waste or toxins from the gastrointestinal tract. By promoting rapid bowel emptying, cathartics can help address issues such as constipation or prepare the bowel before medical procedures.

The other options do not accurately describe the primary function of cathartics. While relieving nausea, softening the stool, and reducing inflammation may involve different classes of medications or interventions, these actions fall outside the specific and intended use of cathartics. Therefore, the focus on their ability to evacuate the bowels makes the selected answer the most appropriate and accurate representation of cathartics' primary effect.