An enzyme in grapefruit greatly increases the effect of statin medications.  The potential is to develop a syndrome of spontaneous muscle cells ruptures called rhabdomyolisis.  When enough muscle cells pour out their contents into the blood stream (i.e. myoglobin, creatinine kinase) the kidneys become clogged resulting in complete kidney failure.  A life time of dialysis treatments or a kidney transplant from a compatable donor could be the overall result.