Oral sprays bypass the digestive system but not the liver or kidneys because they receive a major blood supply and have enzymes that process some of these nutrients (plus food and other drugs!). if they've got kidney issues they might want to check everything prior to taking, but magnesium is a key one that they really need to be careful with. this is because kidneys are sensitive in their function when it comes to how much salt we have in the body (potassium and magnesium being the main ones)