In the course of his stay in Gabon, Griffon du Bellay collected 450 plant species, recording ethnobotanical information concerning their various uses. Most notable among these were the powerful stimulant and hallucinogen "Tabernanthe iboga" (family Apocynaceae), used in the indigenous Bwiti religion, and the legume "Griffonia simplicifolia", which is rich in the serotonin precursor 5-HTP. He also encountered the use of "Strophanthus hispidus" (family Apocynaceae) as an arrow poison. He later displayed his plant collections in an exhibit at the Exposition universelle d'art et d'industrie de 1867, for which he won two medals.