Hypotension is when someone has abnormally low blood pressure. But your blood pressure is sure to soar when you notice that the blue in the toilet isn’t from your toilet cleaner. There are medications used to treat hypotension that contain methylene blue, and this substance is known to turn urine blue. It’s more likely that the methylene blue will cause your urine to be more of a green when eliminated. Reaching a true blue isn’t as common, but is totally possible.