Decaffeinated Tea

CO2 / Carbon Dioxide - CO2 decaffeination uses highly compressed carbon dioxide gas, which becomes a fluid under pressure. CO2 is totally safe and is effective at removing caffeine. The CO2 process is good at preserving flavor; its main downside is that it is expensive.
Ethyl Acetate - Ethyl acetate is a naturally occurring compound, common in fruit (and also occurring in small concentration in tea leaf). It is completely safe at the levels in which it remains in the tea after decaffeination. The ethyl acetate process is inexpensive, but it has the disadvantage of removing more flavor than other methods.
Methylene Chloride / Dichloromethane - Methylene chloride, also called dichloromethane, is effective at extracting caffeine while leaving other flavors intact. However, it is a probable carcinogen and is toxic in large concentrations. Its use in decaffeination is legal in the U.S., but regulated by the FDA. Methylene chloride probably does not pose a large health risk in the low concentrations left in most decaf tea, but teas analyzed in the past have been found to have levels exceeding the legal limit. Companies using this process generally do not announce it due to the negative public perception of this chemical.
Benzene - The original decaffeination processes used benzene as a solvent. Benzene is a dangerous chemical and can cause cancer and numerous other health problems. It is not safe for use in decaffeination, and fortunately, its use for this process has been banned and discontinued long ago.
Trichloroethylene - Another organic solvent that has been banned and discontinued for use in decaffeination, trichloroethylene was abandoned after it was found to cause liver tumors in mice.