Harmala´s do definately cause a shift in brainwave patterns, automatically causing a meditative state, synchronising the brain hemnispheres. Teanine (green tea) also does this, but without heavily affecting all kind of abilities like motorics. You can savely partake in traffic after having drunk green tea.

Iboga also has these effects on the brain, in a subtle way when microdosed and ofcourse in a much more extreme way when taken in larger amounts.

I find many hallucinogenic´s like LSD not very meditative. Some people claim that LSD has virtualy no effect on the left brain hemnisphere, so if that is true it is also not likely to cause the synchronisation of the brain hemnisphere´s that is typical for the meditative state.

This idea of ananda bosman has also come to my mind though: some hallucinogenic substances seem to dramatically increase feedback-loops in the brain, so you may expect this to cause some kind of brainwave interference. Especially when you´re in a dark place with little sensory stimuli, you may expect brainwaves to cause interference patterns with themselves. If this is indeed true, than you could maybe expect some sort of brainwave oscillation to take place, leading to indeed a higher level of brainwave coherence, just like oscillation contributes to the coherence of lightwaves in a LASER.