It’s because of the receptors in your brain the molecules attach to. Each neurotransmitter has a different physiological effect when it’s released. Ethanol binds to GABA receptors in the brain which is an inhibitory neurotransmitter. Kinda works in a similar way to an anxiolytic (an anti-anxiety medication). They bind to the GABA receptors and that, in turn, decreases nerve transmission, which decreases neuronal excitability. One of the physiological occurrences is vasodilation