I've done both Harmaline HCL and FB. I lean towards HCL, it dissolves better. I hear you about some of the burning from the MAOI though, and just know that lower butthole is really sensitive, tons of nerve endings, but upper rectum not so much. So you may find a deeper injection help out? You may also get micro-tears from tightness and that'll be a burn too.
(I made a suppository once, and it just slow burned for a while, so I'm really not keen on trying a slow release method again.)
YMMV on solubility, I too can't get some to dissolve in water all the way which is no surprise though (see my copy/paste of beta-carb solubility below). It may turn out to be more of a suspension.
Let us know how it goes! I recently trip sat a buddy who did 30mg of MAOI rectally and that was enough to extend a vape-trip to about double his breakthrough time, and he was "harmalized" for an hour - a second vaping at t+60 got extended and smoothed out like the first. I'm leaning towards needing more like what Jees says, in the 75 mg range for deep harmalization.
Keep the good news coming!
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Harmine : Insoluble in: Basic water, diethyl ether. Low solubility in distilled water.
Isolation:To separate from harmaline, using pKa properties, raise pH of solution containing both alkaloids to pH 8.75 to precipitate 92% of harmine and only 8% Harmaline. Filter to retrieve precipitated alkaloids, and raise the pH further to retrieve the bulk of harmaline
Harmine HCL:Soluble in water, Insoluble in salt-saturated water
Harmaline :Slightly soluble in basic water, poorly soluble in distilled water. Reasonably soluble in acetone (at 25°C, acetone can dissolve 4mg/ml mixed harmalas)
Isolation: To separate from harmine, using pKa properties, raise pH of solution containing both alkaloids to pH 8.75 to precipitate 92% of harmine and only 8% Harmaline. Filter to retrieve precipitated alkaloids, and raise the pH further to retrieve the bulk of harmaline.
Harmaline HCL : Soluble in water, Insoluble in salt-saturated water