Isomers of the same molecule, although very similar, often have different effects. For instance, the right-handed isomer of methamphetamine, dextromethamphetamine, is the most potent human stimulant known: This is the “meth” that tweakers crave. But the left-handed isomer of methamphetamine, levomethamphetamine, is a vasoconstrictor with little to no psychoactive effect and is used in nasal decongestants and inhalers.
In contrast, both isomers of amphetamine are psychostimulants, so Shire combines both the l- and d- isomers in Adderall, each packaged in two different types of salt carriers. By creating a custom racemic mix of l- and d- isomers, and by using a custom blend of salt carriers for each molecule, Adderall meets the definition of an amphetamine formulation that can be patented for prescription use. In a word: genius.
Formulating the perfect blend of speed for children sounds like a task more suited to a crime syndicate than a pharmaceutical company, but Shire put some serious thought into packaging amphetamine into pills for kids with short attention spans. The l- isomer of amphetamine, levoamphetamine, packs a euphoric rush of norepinephrine for a quick and speedy high, with a small release of dopamine for a short period of increased alertness and focus. Levoamphetamine (a.k.a. benzedrine) is a favorite of tweakers who want the most bang for their buck. The d- isomer of amphetamine, dextroamphetamine, produces less of an initial rush but increases the supply of dopamine and norepinephrine in the brain’s synaptic clefts for many hours. Dextroamphetamine (a.k.a. dexedrine) is considered by many to be the first “smart drug,” used experimentally to increase focus, memory, and intelligence.