What Is Tetrahydrozoline?

Tetrahydrozoline is a liquid medication that people use for relieving eye redness as a result of minor eye irritation, thus making it a decongestant. The common cold, allergies and swimming are some of the causes of such a condition. Tetrahydrozoline may be best known by the brand name Visine, an eye-drop treatment that United States pharmaceutical and cosmetics company Johnson & Johnson produces and markets. Other brand names and alternate terms for the medication include Opti-Clear, Murine Plus and Clarif-Eye.

Being a decongestant makes tetrahydrozoline similar to other medications such as oxymetazoline, xylometazoline and naphazoline, all of which are derivatives of a heterocyclic compound and inhibitor of a histamine nitrogen compound called imidazoline. Oxymetazoline and xylometazoline, however, work as nasal decongestants in the form of sprays. Naphazoline, like tetrahydrozoline, is manufactured as an eye medication. In a few instances, though, tetrahydrozoline is available as a nasal spray as well. This characteristic makes it the most flexible imidazoline derivative.

Tetrahydrozoline relieves eye redness and irritation by narrowing the eye's blood vessels for a limited period of time. Some brands of the substance may include lubricants, which have the added effect of preventing further redness and irritation. People can use it up to four times a day or according to the instruction of their physician.

Side effects of tetrahydrozoline include blurred vision, a burning or stinging sensation of the eye, and increased redness or irritation of the eye. People who use tetrahydrozoline should contact their doctors if these signs persist. If more serious side symptoms of this substance occur, such as rapid or irregular heartbeat, headache, nervousness, swelling or sweating, patients should visit their doctors immediately. Also, prolonged use of the treatment—beyond three to four days at a time—may increase the possibility of blood vessel damage in the eye of administration. People with medical conditions such as glaucoma, diabetes, drug allergies, hypertension, heart disease or thyroid disorder must inform their physicians to determine whether taking the medication will be safe.

The U.S. Food and Drug Administration (FDA), the federal agency that is responsible for regulating pharmaceutical use in the United States, places tetrahydrozoline in pregnancy category C. This is a middling category in the FDA's classification system regarding drug risks to fetal health. Although there is a general lack of well-controlled human studies, some animal reproduction studies have yielded evidence of harm to the fetus. Thus, pregnant women must consult with their doctors to see if the benefits of tetrahydrozoline outweigh the risks.