Tetrahydrozoline (THZ)

Tetrahydrozoline, a derivative of imidazoline, is found in over-the-counter eye drops and nasal sprays. Other derivatives include naphazoline, oxymetazoline, and xylometazoline. Tetrahydrozoline is an alpha agonist and its main mechanism of action is the constriction of conjunctival blood vessels. This serves to relieve the redness of the eye caused by minor ocular irritants. An urban legend suggests that tetrahydrozoline can cause violent diarrhea if administered orally, such as by putting a few drops of Visine in an unsuspecting person's beverage. However, the actual results of the "Visine Prank" may be worse, varying from severe nausea and vomiting to seizures or a coma. Diarrhea is not a side effect. Tetrahydrozoline can be synthesized in one step by the heterocyclization of 1-cyanotetralin with ethylenediamine.