I've seen lots of debate, information, misinformation about the alkaloid content of Caapi & Peganum Harmala. I'll attempt to summarize a bit below...
B. Caapi Alkaloid Profile from Wikipedia:
Harmine, 0.31-8.43%
Harmaline, 0.03-0.83%
Tetrahydroharmine, 0.05-2.94%
S. Rue Alkaloid Profile from Wikipedia:
Harmane, 0.16%
Harmine, 0.44%โ1.84%โ4.3%
Harmaline, 0.25%โ0.79%โ5.6%
Harmalol, 0.6%โ3.90%
Tetrahydroharmine, 0.1%
Total harmala alkaloids were at least 5.9% of dried weight, in one study.
Vasicine (peganine), 0.25%
Vasicinone 0.0007%
Erowid's Opinion:
P. harmala, or Syrian Rue, is the plant from which harmine was first isolated, as well as a source of harmaline and tetrahydroharmine. Total beta-Carboline content runs almost 4% by weight in the seeds of Syrian Rue. These alkaloids occur in roughly the same proportions as in B. caapi. Ten grams of Syrian Rue seeds provide about 400 mg of total beta-Carbolines, about that amount in a typical dose of ayahuasca.
http://www.erowid.org/pl.../syrian_rue_info4.shtml
Scholarly HPLC/NMR Analysis:
http://www.ajur.uni.edu/...0et%20al%20pp%201-4.pdf
As is highly evident, various tests can produce some surprisingly different results, leading me to believe that Syrian Rue alkaloid content must vary sharply dependent on something. Growing conditions, climate, age, etc... More study would be most interesting.
It would appear harmalol is very much present, but articles analyzing effects are difficult to find.
Also, it would seem that erowid's article is at least semi-accurate. The alkaloid ratio profiles of the two plants seem very much closer than most care to admit, unless I am reading it wrong. The only notable difference is that some specimens of Caapi can contain a lot more THH. However, in my experience, can and do are quite different

.
I'd love to hear or read any qualitative or quantitative feedback in regards to this. I find this area of discussion highly interesting as RIMA/MAO-I information appears to be reported in a skewed manner compared to the analysis I've read.
~A Fellow Traveler~