Amphetamines affect mood and cognition

The argument

Amphetamines are the clearest illustration of how a stimulant elevates alertness and mood, because the behavioural changes they cause can be traced directly to what they do to neurotransmitters in the brain. The two that matter are dopamine and norepinephrine, the main neurotransmitters involved in the brain's reward and executive function pathways — the systems that register something as worth pursuing and that govern attention, planning and self-control. A drug that raises the availability of those two messengers is therefore not acting on mood and alertness at one remove; it is acting on the machinery by which mood and alertness are set. Amphetamine use increases the release of dopamine and causes it to accumulate rather than be cleared at the usual rate. Because the reward pathway reads dopamine signalling as a marker of significance and pleasure, that accumulation is experienced as euphoric feeling, and because the same pathway feeds executive function, the drug can also affect sexual desire and cognitive and behavioral control. Elevated norepinephrine levels act on a different register, stimulating locomotion and motor control, which is what gives amphetamines the potential performance-enhancing effects that have been exploited by some athletes. The same mechanism accounts for the drug's costs, which is why this is not merely a description of a pleasant effect. Amphetamines are highly addictive precisely because they commandeer the pathway that assigns value to experience, so the drug comes to be treated by that system as the most significant thing available. The psychological and neurological impacts of withdrawal can be extreme, including depression, anxiety, fatigue, and an overwhelming urge to consume more amphetamines. Long-term use alters dopamine receptors themselves, and once the receptors have adapted the change outlasts any single dose, resulting in both cognitive and motor impairments. The elevation of alertness and mood and the damage that follows are two consequences of a single pharmacological action.

Premises

Counter-arguments

A rebuttal is that the argument's own emphasis undercuts the position it supports. The euphoria and heightened alertness it describes are acute, dose-dependent effects; the same drug, in withdrawal or with chronic use, produces depression, anxiety, fatigue and cognitive impairment. So "elevate alertness and mood" characterises only one phase of amphetamine action, not its overall effect. Critics add that the premise's stress on addiction and lasting impairment cuts against the tidy claim that stimulants straightforwardly "elevate" mood and cognition, since the net effect over time can be the reverse of elevation.

Rejecting the premises

[Rejecting P2] The euphoria and stimulation are acute, dose-dependent effects; in withdrawal or chronic use the same drug produces depression, anxiety and cognitive impairment, so "elevate mood" describes only one phase. [Rejecting P3] The premise's own emphasis on addiction and long-term impairment cuts against the position that stimulants simply "elevate alertness and mood," since the net effect over time can be the reverse.