Tetrahydrozoline

Tetrahydrozoline is a sympathomimetic drug used as an over-the-counter nasal decongestant and ophthalmic vasoconstrictor. It is an imidazoline derivative that acts as an agonist at alpha-adrenergic receptors, producing constriction of vascular smooth muscle.

In nasal products, tetrahydrozoline reduces swelling of the nasal mucosa to relieve congestion. In ophthalmic preparations, it constricts conjunc­tival blood vessels to lessen eye redness. Formulations are typically low-dose solutions, with nasal sprays or drops and ophthalmic drops commonly labeled around 0.05% to 0.1% strength.

Onset is rapid for both routes, often within minutes, and the effects last about 4 to 6 hours. Because symptoms can return after the drug wears off, continued use beyond a few days can lead to rebound congestion (rhinitis medicamentosa) or persistent conjunctival redness.

Adverse effects are generally minor but can include burning or stinging of the nose or eye, dryness, and, less commonly, systemic effects such as tachycardia, hypertension, dizziness, or nervousness if absorbed in larger amounts. Serious cardiovascular effects are rare but more likely with excessive use or underlying conditions. Caution is advised in patients with cardiovascular disease, hypertension, diabetes, thyroid disorders, or elderly individuals. Ocular formulations may irritate the eye and should not be used with contact lenses, which should be removed before use.

Interactions may include other sympathomimetics or monoamine oxidase inhibitors. The drug should be used at the lowest effective dose and for the shortest duration. In case of overdose or ingestion, medical attention should be sought promptly.