Amphetamine, also known as speed, is a synthetic stimulant used to suppress the appetite, control weight, and treat disorders including narcolepsy and ADHD. It is also used recreationally and for performance enhancement. These (latter) uses are illegal in most countries.  he term amphetamine causes a certain amount of confusion because it is often used incorrectly. Loosely, amphetamine can describe other drugs with similar, stimulant effects, namely methamphetamine and methylphenidate. Chemists often use the term "amphetamine class" to describe chemicals that are structurally similar (and often similar in effect as well) to amphetamine--namely, chemicals with an ethyl backbone, terminal phenyl and amine groups, and a methyl group adjacent to the phenyl. A large number of chemicals fall into this category, including the club drug MDMA (Ecstasy) and methamphetamine. It is important to note that such an "amphetamine class" does not technically exist. Phamacodynamically, these drugs all fall under the umbrella of central nervous system stimulants; chemically, they are phenylethylamines. Amphetamine, for example, is methylated phenylethylamine, and methamphetamine is double methylated phenylethylamine.