Patients who are candidates for taking laxatives should inform their physician about any previous allergic reactions to laxatives or other substances, including foods, preservatives or dyes. 

Patients who have kidney disease should not use saline laxatives that contain magnesium, potassium or phosphates. Kidney problems can cause these substances to build up in the body. Osmotic agents may cause fluid retention in people with kidney or heart problems. Patients with diabetes are urged to use caution, because laxatives often contain high levels of sugar. Patients with high blood pressure or heart disease are also urged to use caution, as many laxatives contain high levels of sodium.

Swallowing difficulties can also present problems for users of oral laxatives. Difficulty swallowing can cause the lubricant laxative mineral oil to enter the lungs, which may result in pneumonia. Bulking agents can also become lodged in the esophagus of patients who have difficulty swallowing.

Use of laxatives is common among individuals with bulimia nervosa, an eating disorder characterized by a pattern of binge eating followed by harmful purging behaviors, including self-induced vomiting and inappropriate use of laxatives. Therefore, laxative use is not recommended for patients with a history of this disorder.

Patients who are not good candidates for laxative use may benefit from other treatments, such as biofeedback. In fact, recent research indicates that biofeedback may be more effective in alleviating certain types of constipation than laxatives. In addition, researchers are currently studying the benefits of alternative types of medications in treating chronic constipation.