It's not actually gum but a pill. It's an extract from a tree in the Mediterranean islands. Pharmaceutical companies use it in the production of pills and capsules, in self-absorbing surgical threads, and doctors use it for sticking a septic bandage on a surgical wound. It's also used in some alcoholic drinks to prevent stomach damage.

Mastic gum has been shown to be helpful for people with peptic ulcers especially those caused by h-pylori since it has been shown that mastic gum kills h-pylori. It is also promoted to help gastritis and some folks here have used it for that (myself included).

Do a internet search on mactic gum and you will find loads of info.