Original: On November 23, 2007, the use and trade of Pseudoephedrine in Mexico was made illicit, as it was argued that pseudoephedrine was extremely popular as a precursor in the synthesis of methamphetamine.
Simplified: Some countries started to replace Pseudoephedrine by other drugs, such as phenylephrine. The reason for this is that pseudoephedrine can be used to make methamphetamine, which is an illegal drug.