IIUC, synthetic THH is racemic, while the naturally occurring one in caapi is d-THH.

It's speculated that the brewing process may convert one isomer to the other, and also that some of the harmaline may undergo reduction, which would then be racemic. But neither has been confirmed (?)

The analysis of ayahuasca brews has shown roughly equal amounts of harmine and THH.
However, when I take harmine with synthetic THH, my subjective THH effects (and perhaps even more so, the afterglow) are much stronger than when I drink brews. This would suggest the racemic mix is more potent than d-THH, because l-THH is more potent than d-THH?