From everything I've read it appears as if the real concern is with drug interactions. With daily Caapi dose, for most people, they are drinking under what is needed for full MAO inhibition, but as you pointed out Burnt, not everyone metabolizes these things at the same rate.
Combining any MAOI with any of the list below is a bad idea:
Cocaine
Amphetamines
Ephedra
Opiates
Benzo's
BP meds
Some asthma meds
MDMA or any analogue
Any stim for that matter
SSRI's (would NOT mix these two ever, in fact waiting 6 weeks after last SSRI does is highly advisable, they can stay in your system for a long, long, long time).
This is by no means a comprehensive list. If doing a dieta with Caapi it is advisable to not use any OTC/perscription medication unless it is certian that it is not contraindicated for use with MAOI's.
Even at subMAO inhibition levels, it is advisable to stay on the safe side of things.