When I took the barley grass for the first time, it was like the 3-day period, but slightly less intense and only lasted eight hours. I only took a fraction of the capsule, not wanting to feel drowsy the next day.
Here is the weird part: the grass capsules were 0.3 MICROGRAMS/piece. Apparently, smaller doses are sometimes more active, at least according to the websites that peddle this stuff. :? This is an extremely small amount compared to regular supplements, but blood levels are measured in picograms, so it's not impossible to rule out. There is NO placebo effect that could make me shit so many times on command, let alone to the point of dehydration, I am not making this up, I am saying it warrants further research! Something has to change the bioavailability.
Baffled but intrigued... oh LORD! I think I took a whole capsule the second night I tried. That was when things went out of control.
I did not go to work. The peak lasted through the first day, and I did three things: thrashed around in bed while hallucinating violently, ran to the bathroom while my body ejected everything violently, and in the moments of calm (shaking) spent time on the phone with an awesomely supportive sitter.
It was deeper and dreamier than Ayahuasca... I remember being able to see into my body (neon veins, organss, etc.). When I did sleep, I had insane dreams that dealt with a lot of very early childhood issues, it got very lucid at points. The last two days calmed down a bit, there were moments I felt sober and other moments where it just started soaring up again out of nowhere, color sharpness, panic and tremors. Having the sense to check pupils was not present. (It sucked to be caught OFF GUARD because I am all for RESPONSIBLE and PREPARED tripping! :evil: )
Later on, I got into Montmorency cherries. There are apparently some speedy compounds in barley grass (hordenine for one, not sure what else could have synergized). The cherries produced all of the psychedelic effects--IDENTICAL to what I experienced with the grass, again, unique from Ayahuasca/mushrooms--with NONE of the nasty OMG-am-I-going-to-die side effects I got from the grass. There was a bit of purging in the beginning, but nothing beyond what any other kind of cherries would do normally.
20 Montmorency cherries are 0.15 micrograms of melatonin. I found that my requirements varied depending on time of month, what I had eaten in the day, lots of factors. I've had effects from as little as 5 cherries, and other disgruntled nights where I've eaten as many as 60 to sleep, but with no avail. 20 was a good number while I was microdosing/in crazy diet mode.
Currently, I'm taking ~12 cherries before sleep without any Caapi, I sleep well, have insane dreams, and see a bit of patterns and feel light and floaty while I fall asleep. That's really all I want from melatonin in my life at this point, as far as hallucinations are concerned.
Interestingly enough, I have a friend who takes upward of 10mg with Ayahuasca to remain in a more calm, meditative state. That is a comparitively massive dose. He said he was envious and puzzled by my results (as I flopped around, teeth chattering and clenching my gut, "ENVIOUS?! :evil: "

). Other people have said melatonin "smooths out" the comedown with Ayahuasca/mushrooms.
From my experience, dose, diet, and the time/sequence of ingesting melatonin and harmalas all seem to impact how intense an experience will be. Will nothing happen? Will you sleep peacefully? Or will you fly off the handle?
Writing this off to "placebo," "power of suggestion," etc., is simply ignoring a phenomenon that repeatably and reliably can be made to happen in my body, just like smoking DMT can repeatably and reliably produce equally altered states of consciousness in my brain. So. It's pretty weird and I wish I could find some more information!!
Glad to see a revived interest in the subject, personally!

I think there's lots to learn...