How do drugs affect the brain?

Alcohol depresses the central nervous system

Question: How do drugs affect the brain?
Position‹2 of 3›: Depressants slow brain and nervous system function
Argument‹3 of 4›: Alcohol depresses the central nervous system

Alcoholic beverages are psychoactive due to the effects of ethanol on the brain and nervous system.

The argument

The active compound in alcoholic drinks, ethanol, works on two of the brain's most important neurotransmitters, the molecules which transmit signals between networks of neurons. Ethanol increases the effects of gamma aminobutyric acid, the primary neurotransmitter which inhibits neuronal signalling, and suppresses the effects of glutamate, the major excitatory neurotransmitter. The combined impact of these interactions on the brain is to slow neural function, lowering reaction times, worsening cognitive abilities, and enhancing sociability by lowering anxiety and social inhibitions. Consumption of large quantities of alcohol can eventually depress brain activity to the point of unconsciousness or even death, and over a longer period of time, alcohol consumption is associated with a decrease in brain volume.

Premises

[P1]Ethanol, the active compound in alcohol, increases the inhibitory neurotransmitter GABA and suppresses the excitatory neurotransmitter glutamate. [P2] This combination slows neural function, lowering reaction times and impairing cognition, and in large quantities can depress brain activity to unconsciousness or death. [C] Therefore, alcohol acts as a depressant that slows the brain and central nervous system.

Counter-arguments

Some qualify this picture rather than reject it. Classifying alcohol as a pure 'depressant' is a simplification: at low doses it can be behaviourally stimulating — increasing talkativeness, confidence and activity — because its early disinhibiting effect on the prefrontal cortex produces excitation before the broader sedative effect dominates, which is why pharmacologists describe it as biphasic. Its action is also not confined to GABA and glutamate; ethanol modulates dopamine, serotonin, endorphin and other systems, which is what drives its rewarding and addictive properties. So while alcohol does ultimately slow the central nervous system, describing it solely as a depressant that 'slows brain function' omits the stimulant-like and reward effects that also characterise how it acts on the brain.

Rejecting the premises

[Rejecting P1] Ethanol acts on many neurotransmitter systems beyond GABA and glutamate — including dopamine, serotonin and endorphins — so the two-neurotransmitter account is an incomplete picture of its brain effects. [Rejecting C] Alcohol is biphasic: at low doses its disinhibiting effect is behaviourally stimulating, so classifying it purely as a function-slowing depressant omits its excitatory and rewarding phase.