The amount of the chemical in grapefruit juice is highly unpredictable from glass to glass. Long before the chemical in grapefruit juice was identified, doctors were advising patients who took certain medicines to avoid grapefruit juice. When scientists removed the chemical from grapefruit juice, the juice no longer affected how certain medicines were absorbed. Grapefruit juice is less expensive than most of the medicines with which it interacts.
While grapefruit juice is a healthy drink, it has been discovered that a chemical in the juice affects how certain medicines are absorbed, with the result that normal medicinal doses act like higher doses. Getting the wrong dose is dangerous. Since it is always desirable to take the lowest effective dose, the best medical approach would be to take lower doses of these medicines along with prescribed amounts of grapefruit juice.
Which one of the following, if true, most seriously weakens the argument?