The report last month that grapefruit juice increases availability of some drugs to your system is not new, but not well known.
Anti-cholesterol drugs (lovastatin or Mevacor, for example) immunosuppressants (for example, cyclosporine), and certain psych meds (e.g., buspirone or Buspar, carbamazepine or Tegretol, diazepam or Valium) all can go up when taken within 12 hours of grapefruit.
How much does it take? Just one 8 ounce glass. Or the whole fruit can do the same thing.
Grapefruit juice has furanocoumarins (psoralens) which act in the liver to change drug metabolism. But it’s probably many components.
There’s no juice gambling with your health. And besides, orange juice doesn’t have the same effect.