Most over-the-counter eyedrops used for treating red eyes, contain tetrahydrozoline which is FDA approved for use in the eyes.
Some of the brands that contain the chemical are Visine, Murine Plus and Clarine. The labels specifically state that they are for external use only and to keep them out of the reach of children.
However, the misuse of these eyedrops by consuming them orally, can cause overdose symptoms. Tetrahydrozoline passes quickly through the digestive tract and into the blood and central nervous system. Overdose symptoms include drowsiness, decreased breathing and slow heartbeat which can lead to coma and death.
Most cases of poisoning by these drops are accidental and happen with children or pets. Most eyedrop bottles contain 15 to 30 milliliters of solution and a dose as low as 1 to 2 milliliters can be toxic to children. If you suspect that these eye drops have been ingested, do NOT induce vomiting, perform CPR if necessary and seek immediate medical attention.*