Dosage recommendations for terpin hydrate with codeine are 10 to 20 milligrams every four to six hours for adults, states the University of Maryland Baltimore Washington Medical Center. Children ages 2 through 6 need 1.25 to 2.5 milliliters, and children ages 6 through 12 use 2.5 to 5 milliliters.
Terpin hydrate loosens mucus, states MedicineNet. Terpin hydrate comes from various sources such as turpentine, oregano and thyme, reports Wikipedia. The Food and Drug Administration bans terpin hydrate because there is no proof of its effectiveness, as of 2015. This ban has been in place since the 1990s, although before the ban, terpin hydrate was a common treatment method.