Why do you lose your appetite when taking cold and flu tablets?

Most cold and flu tablets contain pseudoephedrine, which is a stimulant and may cause you to lose your appetite.

pseudoephedrine is extracted from these tablets to make methamphetamine, most people who use meth don't eat much which is why drug addicts are usually skinny (also they most likely spend their food money on drugs, good thing they don't have an appetite...)