It was proposed that ginko may potentiate monoamine oxidase (MAO) inhibitors (speculative),150 due to the evidence that EGb7671 and the fresh and dried leaves and flavonoids including isorhamnetin and especially kaempferol inhibit MAO-A and MAO-B (in vitro).786,,916 One individual taking 4 capsules of ginkgo standardized extract had a 30% and 50% inhibition of human platelet MAO-B after 1 and 3 hours, respectively, and drinking a tea made from 2 grams of dried leaves reduced platelet MAO-B by 29% after 1 hour (PO in human case study).786
      HOWEVER, no effects were shown on mouse or rat brain MAO or concentrations of bioamines (ex vitro) when rats were given 10mg/kg kaempferol or 15 mg/kg ginkgo extract orally 3 hours prior.916 Based on behavioral evidence, no MAO inhibition was found with 100 mg/kg standardized ginkgo extract EGb 761, except for slight excitation from 100mg/kg tryptamine given intravenously (PO in mice).1053 In 10 subjects taking 120 mg/day of ginkgo extract EGb 761 for 1 month, no significant changes in brain MAO-A or MAO-B were measurable (PO in human study). This does not rule out the possibility of MAO inhibition occurring outside the brain that might lead to significant interactions.615
      High concentrations of the concentrated extract EGb 761 inhibit uptake of serotonin (in vitro) and dopamine (in vitro).193
      HOWEVER, lower concentrations (achieved in vivo with a dose of 100 mg/kg) increase serotonin uptake by synaptosomes (in vitro, PO in mice) and do not affect dopamine uptake (in vitro).192

Extracts of Ginkgo biloba leaves produce reversible inhibition of rat brain monoamine (MAO). Both MAO-A and -B types were inhibited to a similar extent. The MAO inhibitory compound(s) were present in dried or fresh Ginkgo biloba leaves as well as in commercially available capsules of Ginkgo biloba and appear to be heat stable with relatively low molecular weight. MAO inhibition by Ginkgo biloba may be a mechanism underlying reported anti-stress and anxiolytic activities of this natural product.