Mucinex D and Maximum Strength Mucinex D contain the active ingredient pseudoephedrine (PSE), which is a nasal decongestant that relieves sinus pressure and congestion. This ingredient is also used in the illegal manufacturing of methamphetamine, commonly known as “meth”, a highly addictive stimulant. In 2006, Congress passed a law to stop the illegal use of PSE by banning the over-the-counter sales of cold products containing PSE, and limiting the monthly amount any individual could purchase. The product is stored in a secure location where consumers do not have direct access. Mississippi and Oregon have gone further to reduce the misuse of PSE and require a prescription to purchase Mucinex D and Maximum Strength Mucinex D. In the other 48 states, only an ID is required at point of purchase.