Mastic Gum supports stomach and duodenal health. Mastic Gum supports the health of the gastric and duodenal cells and tissues to promote gastrointestinal health. It features resin from the mastic tree (Pistacia lentiscus), also called mastiha, a shrub-like tree grown mainly in Greece and Turkey. Composed of a resinous exudate containing essential oils, mastic gum has been used for centuries.