Several flavonoids have been identified as inhibitors of MAO-A and MAO-B. The flavonols kaempferol and quercetin and the flavones apigenin and chrysin were isolated from a standardized Gingko biloba extract. All four flavonoids were identified as MAO-A inhibitors with IC50 values of: kaempferol (0.7 μM), apigenin (1 μM), chrysin (2μM) and Quercetin (5 μM). Phenelzine, a non-selective and irreversible inhibitor of MAO was used as a reference compound (IC50 value 0.04 μM).

Fruits and vegetables particularly citrus fruits, apples, onions, parsley, tea, red wine, etc. are the primary dietary sources of Quercetin. Olive oil, grapes, dark cherries, and dark berries such as blueberries and bilberries are also high in flavonoids including Quercetin. Studies were conducted on the flavonoids (Myricetin, Quercetin, Kaempferol, Luteolin and Apegenin) contents of 62 edible tropical plants. The highest total flavonoids contents were found in onion leaves (1497 mg/Kg Quercetin, 391 mg/kg Luteolin and 832 mg/kg Kaempferol) followed by semambu leaves, bird chillies, black tea, papaya shoots and guava. Major flavonoids content in these plant extract is Quercetin, followed by Myricetin, and Kaempferol. In vegetables, Quercetin glycosides predominate but glycosides of Kaempferol, Luteolin and Apegenin are also present. Fruits contain almost exclusively Quercetin glycosides, whereas Kaempferol and Myricetin glycosides are found only in trace quantities.

‘Dieta’ undertaken, sometimes for a week or more before psychoactive brews are taken ceremonially in traditional cultures. It stands to reason that loading the body beforehand with high amounts of flavonoid containing plants would only help the MAOI process, effectively boosting the potency of the psychoactive brew once it was administered.

nen888 has reportedly activated acacia extract with Passiflora incarnata, which has high levels of MAOI flavonoids and relatively little harmala alks.

this is the first time the details of a 1996 p. inacarnata + acacia extract huasca experiment have been released outside of the ethnobotanic research community: (an incarnata vaporized extract experiment is referred to in Voogelbreinder 2009)

"...approx. 1kg of purchased dry passiflora incarnata stem & leaf was boiled X3 in rain water...the large amount of liquid was combined and reduced over several hours, turning increasingly dark purple/brown and thick..,while still possible it was filtered several times through fine cheesecloth...a point of viscosity was reached at which 1 hypothesized dose (333grams of herb) equalled a large glass or coffee mug of thick liquid (the aromas during the process were noted to be somewhat mildly psychoactive)
...A dosage of estimated at = 400 grams herb was consumed by two subjects...5 minutes afterwards approx. 50-70mg of a. obtusifolia extract as the freebase was rapidly swallowed and chased with water/lemon juice (to remove the awful freebase aftertaste)
...Within 10 minutes strong sedative and 'anti-depressant' effects from the passiflora were felt...as these grew (without yet tryptamine effects) it was commented that this plant alone was a satisfying experience...A shiny and pleasant 'haze' surrounded lights...At around 90 minutes, after it was pondered that maybe MAO inhibition was not sufficient, tryptamine-like effects (geometries, '4D-ness', auditory) rapidly grew over 10 minutes accompanied by sudden purging...
...Both subjects found the intensity of colors beyond their previous experiments with a. extract and p. harmala or b. caapi...'fantastic bright blues, reds, purples and golden hues.'...It was subjectively judged as more sedative or narcotic than rue or caapi with a strong 'dreaminess'...rue was judged the 'clearest', caapi unique in other ways...
'It made the tryptamines very dreamy, colorful, and beautiful...very feminine.'
...After a linear 'plateau' of 30 minutes, effects gradually subsided over 2-4 hours, with a sense of sedation up to 5hrs afterwards. Overall, it was very positive...'It lacked the punch of rue, but had such a lovely dreamy quality...very sensual...'..."

it is possible some of the MAOI activity was due to the flavonoids Apigenin and Kaempferol, as well as the ß-carbolines harmine, harmaline, harman, norharman and harmol (present at 0.1-0.2% [Hultin]; Gracie & Zarkov claim up to 0.5%)
Flavinoids are present at around 1.5%,or more, in stems and leaves..regarding Kaempferol, also found in Ginkgo biloba, from:
B. D. Sloley et al.
["Identification of Kaempferol as a Monoamine Oxidase Inhibitor and Potential Neuroprotectant in Extracts of Ginkgo Biloba Leaves" Journal of Pharmacy and Pharmacology Volume 52, Issue 4, pages 451–459, April 2000]



some potent MAOI flavonoids include quercitrin, isoquercitrin, rutin, and quercetin, which were isolated from the leaves of Melastoma candidum. They exhibited an inhibitory effect on MAO-B. The IC50 values 19.06, 11.64, 3.89, and 10.89 μM respectively/
["Monoamine Oxidase B and Free Radical Scavenging Activities of Natural Flavonoids in Melastoma candidum "
Mei-Hsien Lee et al. J. Agric. Food Chem., 2001, 49 (11), pp 5551–5555]

..many more plants than previously thought could be effective MAO inhibitors..

i have attached a cool paper on flavonoids and their bio-activity
"Flavonoids and the CNS" Anna K. Jäger and Lasse Saaby Molecules 2011, 16, 1471-1485

Notes for later work :

https://www.ncbi.nlm.nih.gov/pubmed/25915461

https://www.ncbi.nlm.nih.gov/pubmed/29496172

https://scholarcommons.u...le=1324&context=etd

It seems they are Hypericum afrum and Calothamnus villosus but can't say at 100%

The objective was to evaluate the inhibitory effect of Hypericum afrum and Cytisus villosus against MAO-A and B and to isolate the compounds responsible for the MAO-inhibitory activity.

Is Hypericum afrum similar to Hypericum perforatum (Saint John's wort)?