MAOA and major depressive disorder: Herbal natural products have been suggested as important source for inhibitors of MAOs and also support traditional use of these herbal products as alternative for treatment of depression, Parkinson’s disease and other neuropsychiatric as well as neurological disorders [19] Specially, the dietary supplements and herbal preparations containing β-carboline harmala alkaloids show prominent inhibition of MAO-A and have been suggested to be responsible for their psychoactive properties [20,21,22,23].