Pseudoephedrine is the active ingredient in Sudafed, which is a decongestant that helps relieve nasal or sinus congestion caused by the common cold, sinusitis, hay fever, and other respiratory allergies. It works by narrowing the blood vessels in the nasal passages, which decreases swelling and congestion. Sudafed can temporarily relieve sinus pressure and congestion, as well as nasal congestion due to the common cold, hay fever, or other upper respiratory allergies. It is important to read the manufacturers package instructions carefully when self-treating with Sudafed, and to consult a doctor or pharmacist if necessary. Sudafed should not be used to make a child sleepy, and other cough-and-cold medications that contain the same or similar decongestants should not be given to children under 6 years old. When used as directed, pseudoephedrine is recognized by the FDA as a safe and effective treatment option for congestion relief related to the common cold, flu, and allergies.