Tetrahydrozoline is a decongestant used to relieve redness in the eyes caused by minor eye irritations (e.g., smog, swimming, dust, or smoke). It belongs to a class of drugs known as sympathomimetic amines. It works by temporarily narrowing the blood vessels in the eye. Some brands of tetrahydrozoline eye drops may contain lubricants. Lubricants help protect the eyes from more irritation and dryness.