Mastic, also known as mastic gum, is a perennial shrub native to the Mediterranean region. It has small leather leaves and produces small red flowers that bloom in groups. The fruit begins red and ripens into a deep black color. Mastic grows in open areas in the wild, and is also grown in controlled environments where it is cultivated for the resin that seeps from the bark. 
Traditional use of the resin is varied. It is believed that the Egyptians used it for embalming, while the Greeks are believed to have used it as the first chewing gum. Early medicinal uses included skin conditions, respiratory conditions, and treatment of diarrhea. Today, mastic gum can be used as a temporary filling for tooth cavities, and as chewing gum to protect against cavities. It is also employed to protect the stomach and to treat ulcers.
The main constituents are resins, volatile oils, and tannins. The volatile oil is high in pinenes, which are known anti-septic.
The medicinal part of the plant used is the resinous exudates from the stem.
Mastic gum is believed to be protective to the lining of the stomach. It has shown efficacy for the treatment of duodenal ulcers. In study, mastic gum was able to heal ulcers and relieve symptoms associated with ulcers; such as the ‘burning’ pains after eating. 
Mastic gum may also inhibit the growth of H.pylori, known to cause gastric ulcers. Aside from H.pylori, it may also fight other bacteria and fungus in the digestive tract. More research is needed to know the full extent of its protective ability.
Mastic gum may also be used to decrease the formation of plaque on teeth. It can be chewed daily to cause a reduction in the amount of bacteria in the saliva. It is the bacteria in the mouth that contribute to the formation of plaque on teeth. 
The dosage that is effective at treating duodenal ulcers is 500 milligrams, taken 2-4 times daily. The abovementioned study documented a treatment duration of one-month.
There are no side effects associated with the use of mastic gum. However, individuals that may be sensitive or allergic to any parts of the mastic plant should abstain from using supplements containing mastic gum.
1. Chevallier A. Encyclopedia of Herbal Medicine, 2nd Ed. 2000. Dorling Kindersley, New York: 250.
2. Al-Habbal MJ, Al-Habbal Z, Huwez FU. A double blind controlled clinical trial of mastic and placebo in the treatment of duodenal ulcer. Clin Exp Pharmacol Physiol. 1984 Sep-Oct; 11(5): 541-544.
3. Takahashi K et al. A pilot study on anti-plaque effects of mastic chew gum in the oral cavity. J Peridontol. 2003 Apr; 74(4): 501-505.