It is only one enzyme system involved, the cytochrome P450 (CYP), the specific isozyme is the 3A4. DHB is a 'mechanism based inhibitor' of this system. It prevents oxidative destruction of the drug molecule in question. Not just steroids, a lot of things are metabolized by this enzyme (any CYP3A4 substrate) The metabolic pathways for these substrates include N-oxidation, C-oxidation, N-dealkylation, O-dealkylation, nitro-reduction, dehydration, and C-hydroxylation. The first-pass metabolism during the intestinal absorption process is the likely spot of signifigance, as Sldg suggested earlier. That means higher plasma levels and greater effectiveness of the drug. St. Johns wort is a common herb that has the opposite effect. It induces the enzyme and makes your body detox faster. Serzone is a common anti-dep. med that is a potent inhibitor like GFJ and OJ to a lesser extent. Know these interactions, not just to be safe, but to get the most economy out of the drugs that you use! Use buffers for amines like ephedrine. Chew a couple of tums with it and it will extend the t1/2 due to decreased renal clearance. It also promotes fast stomach absorbtion.