In 1989, a group of researchers discovered that drinking grapefruit juice dangerously increased the potency of a certain blood pressure drug. This was due to the juice's interference with the activity of CYP 3A4, an enzyme that metabolizes drugs into less potent forms. Numerous studies since have shown that grapefruit juice affects the potency of drugs used to lower cholesterol and also interferes with the metabolism of SSRIs used to treat depression.