DEAR DR. BLONZ: I enjoy fresh grapefruit juice in the morning with breakfast. Friends have told me that grapefruit juice interferes with the absorption of vitamins, pointing to its interference with prescription drugs as proof. I searched the web for info and found that grapefruit juice interferes with some prescription drugs, but found nothing about it interfering with vitamin absorption. : There is no evidence that vitamin or mineral supplements are affected by grapefruit juice in the same way it affects certain medications. The effect was discovered by accident when grapefruit juice was used to disguise the taste of treatments used in a research study.