Pseudoephedrine (commonly abbreviated as PSE) is a sympathomimetic amine commonly used as a decongestant. The salts pseudoephedrine hydrochloride and pseudoephedrine sulfate are found in many over-the-counter preparations either as single-ingredient preparations, or more commonly in combination with antihistamines, paracetamol and/or ibuprofen. Consumers in North USA, the United Kingdom, and Australia often refer to it as Sudafed, the trademark for a common brand of pseudoephedrine hydrochloride, although Pfizer now sells products without pseudoephedrine under the brand name (as Sudafed PE).

Unlike antihistamines, which modify the systemic histamine-mediated allergic response, pseudoephedrine only relieves nasal congestion commonly associated with colds or allergies. However, some users report rapid and effective relief from other allergic symptoms, including itchy and/or watery eyes, which may not have been provided effectively by antihistamines.

The advantage of oral pseudoephedrine over topical nasal preparations, such as oxymetazoline, is that it does not cause rebound congestion (rhinitis medicamentosa); however, it is more likely to cause adverse effects including hypertension.