It’s used primarily to treat constipation and available over-the-counter but if the dosage isn’t probably adhered to it can be extremely dangerous, even fatal. Sodium Phosphate is the drug that we are talking about and the usual dosage is to be taken no more than once in 24 hours. The problem is that in our “instant relief” world people take it more often than that.
The results can damage organs like the liver, the kidneys and the heart. The problem is seen most often in those who are really young or older as well as anyone who combines the Sodium Phosphate with other medications that may increase the dehydration. Even simple anti-inflammatory drugs such as aspirin and ibuprofen can be a problem.
You can read more about the FDA warning on their website.