Why cant you have grapefruit with some medications

Jessica is a friend dislodge a piece of meat from her throat. she delivers five blows on her friend’s back with her fist and then gives him five abdominal thrusts. is jessica doing the procedure correctly? 1 no, she should use the heel of her hand for the blows. 2 no, she should use the side of her hand for the blows. 3 no, she should use her elbows to deliver the blows. 4 no, she should use a tennis ball to deliver the blows.