Lisinopril is an ACE inhibitor used for blood pressure. One of its side effects is that it tells the kidneys to hold onto potassium rather than flushing it out in your urine. If you take extra potassium (as a supplement or salt substitute) while the lisinopril is already keeping your levels high, the potassium builds up in your bloodstream.
This is a companion discussion topic for the original article at https://patient.info/medication-interactions/lisinopril-and-potassium-interaction