Are you not supposed to drink grapefruit juice when taking valium or xanax (alprazolam)?

Less effect: It may speed up metabolism, and thereby reduce it's effectiveness, but otherwise not of concern.

Correct!: Grapefruit and grapefruit juice can interfere with your body's breaking down medicines like xanax (alprazolam) and valium. They could build up in your system, making you drowsy or having other side effects. Avoid grapefruit juice and grapefruit-containing foods while on these medicines. You can enjoy orange juice, though!