What is Tetrahydrozoline? Tetrahydrozoline is a decongestant ophthalmic solution for the relief of symptoms of conjunctival edema and congestion secondary to allergic reactions and mild eye irritation. But if you use too much, your eyes will become red and swollen. So to find out what is Tetrahydrozoline drug? The following article will help you better understand the uses of Tetrahydrozoline.