Galactogogue
Agent that promotes the flow of breast milk production in humans and other animals.  It may be synthetic, plant-derived, or endogenous.
 

Gastritis
Inflammation of the stomach and intestinal tract usually caused by bacteria, aspirin, non-steroidal anti-inflammatory drugs (NSAIDS), or alcohol.
 

Giardia
A genus of flagellate protozoa some of which are parasitic in the intestinal tract of man and domestic animal; transmitted by ingestion of cysts in fecally contaminated water and food; interfere with the absorption of fats; boiling water inactivates them.
 

Gingivitis
Inflammation of the gums.  It comes from bacteria, debris, food impaction etc. Gingivitis can lead to pyorrhea
 

Glaucoma
Any of a group of eye diseases in which the pressure of the fluid in the eye is so high that it causes damage.  Can cause damaged optic disk, hardening of the eyeball, and partial to complete loss of vision.