Alcohol is by traditional definition a depressant from what I have been taught, ergo it shows down CNS responses.
However, why does alcohol then make some people act out and be more energetic than when they don't drink?
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These types of reactions in pharmacology in general are called paradoxical effects.
The main effect of alcohol on the CNS is the potentiation of GABA receptors. GABA receptors are (mostly) inhibitory receptors in the CNS, so potentiation of GABA receptors mostly decreases brain activity by increasing inhibition.
However, you can distinguish between neural inhibition and behavioral inhibition. Some brain regions, like the prefrontal cortex, seem to primarily have inhibitory effects on behavior. That is, usually prefrontal cortex is active when suppressing actions. If you were to suppress the prefrontal cortex, you would get the opposite effect on behavior. When there is "inhibition of inhibition" the term often used is "disinhibition."
It isn't yet clear why exactly alcohol leads to behavioral disinhibition at lower doses, but this is one possible mechanism. In general, U-shaped dose-response curves are quite common in neuroscience, so alcohol isn't all that unusual in that sense.
Most people experience some stimulating effects from alcohol in small doses. Drinking alcohol, often a person finds increased talkatively, feelings of energy, and desire for action. In small to moderate doses of alcohol, the initial effects of alcohol act like a stimulant. However, alcohol is actually in the depressant class of drug types. Alcohol, like sedatives and tranquilizers, actually slows down activity in the central nervous system. To be more specific, it slows down the activity in the GABA receptors of our brains. The slowing of these systems is responsible for the relaxing quality produced by alcohol. The slowing of the central nervous system is also responsible for the lowered reaction time and dissociation.
Look at this wikipedia article: https://en.wikipedia.org/wiki/Short-term_effects_of_alcohol_consumption