Some over-the-counter laxatives used to treat constipation can have dangerous side effects when used improperly, The USA Today reported.

The Food and Drug Administration issued a warning on Wednesday after reviewing dozens of reports of serious side effects, including 54 illnesses and 13 deaths associated with the oral and rectal use of sodium phosphate laxatives. The drug is marketed under the brand name Fleet, as store brands and as generics.

Fleet brand enemas, oral laxatives and other similar products can result in severe dehydration or dangerous changes in electrolytes, which can damage kidneys and hearts, when taken too often, in the wrong dose or by people with coexisting health problems.

It could also adversely affect those who have kidney disease, bowel obstructions and patients taking other medications that affect kidney function, such as diuretics, drugs to treat high blood pressure and pain relievers such as aspirin and ibuprofen, NBC News reported.

The FDA noted that most of the trouble occurs when people fail to follow the directions on the label and overdose on the drug.

"The bottom line is that these products are safe for otherwise healthy adults and older children for whom dosing instructions are provided on the Drug Facts label as long as they follow these dosing instructions and don't take the product more often, or in greater amounts, than the label instructs," Mona Khurana, a medical officer in FDA's Division of Nonprescription Regulation Development and a pediatric nephrologist, said in a statement.  

Those most at risk for these dangerous - and sometimes deadly - side effects are young children, people older than 55, and adults who already are dehydrated or have kidney disease, heart problems or inflamed colons.

Khurana added that laxatives should not be given to children younger than five years old and younger without talking to a health care provider.