What is the primary action of amphetamines?

Amphetamines primarily act as stimulants that increase the activity of certain neurotransmitters in the brain, particularly dopamine and norepinephrine. This stimulation leads to an increase in central nervous system (CNS) functioning, which includes heightened alertness, improved concentration, and increased energy levels.

The stimulating properties of amphetamines make them effective in treating conditions such as attention deficit hyperactivity disorder (ADHD) and narcolepsy. By enhancing the release and inhibiting the reuptake of neurotransmitters, amphetamines create a state of increased wakefulness and enhanced cognitive performance, which is why "speeding up CNS functioning" is the correct description of their primary action.