There will definately be some substrate competition, but both compounds have a very high therapeutic index so shouldn't be much to worry about.
The level of potentiation is likely not going to be super high, CBD is likely to not gum up cyp3a4 to a large degree.
Strong substrate inhibitors like ketoconazole stick a nitrogen lone pair of electrons into the active iron which impede enzyme cycle.
This is also in contrast to mechanistic cyp inhibitors which contain a reactive group that covalently binds to the enzyme; these permanently disable the enzyme and require new enzymes to be synthesized to regain function.
Think of it like CBD is a bunch of people waiting in line at the dmv. The more. CBD (or alprazolam, but the dose is low enough that it will not be as significant) the longer the wait to the front of the line will be. Ketoconazole is like an angry customer arguing with the dmv person holding up the line for a while but eventually getting through. A mechanistic inhibitor would be like somebody driving a bulldozer through the dmv so that a new building is necessary.
And that's it for today's imprompteau pharmacology lesson.
