Pseudoephedrine is a medication commonly used as a decongestant to relieve nasal or sinus congestion caused by colds, allergies, or hay fever. It works by narrowing the blood vessels in the nasal passages, which reduces swelling and congestion. Pseudoephedrine is often found in over-the-counter cold and allergy medications. While effective, Pseudoephedrine is regulated in many countries due to its potential use in the illegal production of methamphetamine. As a result, products containing this ingredient may require identification for purchase, and there are limits on the quantity that can be bought at one time. Always follow dosage instructions and consult a healthcare professional if needed.