Increase of ectopic pacemaker activity can occur when pseudoephedrine is used concomitantly with digitalis. Antacids increase the rate of pseudoephedrine absorption, while kaolin decreases it. Mechanism of action
Pseudoephedrine is a sympathomimetic amine. Its principal mechanism of action relies on its direct action on the adrenergic receptor system. The vasoconstriction that pseudoephedrine produces is believed to be principally an α-adrenergic receptor response.Pseudoephedrine acts on α- and β2-adrenergic receptors, to cause vasoconstriction and relaxation of smooth muscle in the bronchi, respectively. α-Adrenergic receptors are located on the muscles lining the walls of blood vessels. When these receptors are activated, the muscles contract, causing the blood vessels to constrict (vasoconstriction). The constricted blood vessels now allow less fluid to leave the blood vessels and enter the nose, throat and sinus linings, which results in decreased inflammation of nasal membranes, as well as decreased mucus production. Thus, by constriction of blood vessels, mainly those located in the nasal passages, pseudoephedrine causes a decrease in the symptoms of nasal congestion. Activation of β2-adrenergic receptors produces relaxation of smooth muscle of the bronchi,  causing bronchial dilation and in turn decreasing congestion (although not fluid) and difficulty breathing. Other uses
There have been reports of off-label uses of pseudoephedrine for its stimulant properties. Long-distance truck drivers and athletes, for example, have reportedly used pseudoephedrine as a stimulant to increase their state of alertness/awareness.A study has also found that pseudoephedrine can reduce milk production in breastfeeding women.
)In regards to the identification that may be used by an individual buying pseudoephedrine products the following constitute acceptable forms of identification:

US passport
Alien registration or permanent resident card
Unexpired foreign passport with temporary I-551 stamp
Unexpired Employment Authorization Document
Drivers License or Government issued identification card (including Canadian drivers license)
School ID with picture
Voters Registration card
US Military Card
Native American tribal documentsThe requirements were revised in the Methamphetamine Production Prevention Act of 2008 to require that a regulated seller of scheduled listed chemical products may not sell such a product unless the purchaser:
Presents a government issued photographic identification; and
Signs the written logbook with their name, address, and time and date of the sale

State
Most states also have laws regulating pseudoephedrine.The states of Alabama, Arizona, Arkansas, California, Colorado, Delaware, Florida, Georgia, Hawaii (as of May 1, 2009) Idaho, Illinois, Indiana, Iowa, Kansas, Kentucky, Louisiana (as of August 15, 2009), Massachusetts, Michigan, Minnesota, Mississippi, Missouri, Montana, Nebraska, Nevada, New Jersey, North Carolina, Ohio, Oklahoma, Oregon, Pennsylvania, South Dakota, Tennessee, Texas, Utah, Vermont, Virginia, Washington, West Virginia and Wisconsin have laws requiring pharmacies to sell pseudoephedrine "behind the counter". Though the drug can be purchased without a prescription, states can limit the number of units sold and can collect personal information from purchasers. The states of Oregon and Mississippi previously required a prescription for the purchase of products containing pseudoephedrine.