 Ethanol acts as a depressant within the brain, meaning that it slows down the function of nerve cells. It does this by messing with the brain's neurotransmitters, which it can do because ethanol is such a small molecule that it can pass through the tight capillaries in the brain known as a blood-brain barrier. Neurotransmitters are chemical messengers used by our nervous system to communicate with nerve cells and muscles. There are a number of different types of neurotransmitters, but alcohol mainly affects three, GABA, glutamate and dopamine. Ethanol increases the effects of GABA, which is an inhibitory neurotransmitter, which means it decreases electrical activity in the brain, slowing it down. Ethanol also reduces the amount of glutamate in the brain, and glutamate is an excitatory neurotransmitter, so reducing its effect also slows the body down. Both of these effects are why after a number of drinks we might have difficulty speaking and poor coordination. And dopamine? Well, you would think that the onset of these effects would signal to most of us to stop drinking. So why do we often end up lining up at the bar for another drink? Ethanol increases the amount of dopamine in the brain's reward centre. This increases the feeling of pleasure when we drink. The level of pleasure we derive from drinking is not the same for everyone. Some people's genetic makeup makes them feel considerably more pleasure than others. These people are at high risk of being heavy drinkers and developing alcoholism. And there is a lag between when we consume the drink and when the next level of intoxication kicks in. So you may still feel fine, or at least think you feel fine, as you ask the bartender for another round. There are also social pressures. You're probably drinking with friends or family and could be trying to impress them, or at least keep up with them, reacting to peer pressure and family or cultural expectations. So, you're feeling pleasure, your inhibitions are lowered, you're reacting to a social pressure to drink, your judgement is impaired and your body is still two drinks behind your enthusiasm. Really, you have to have pretty good self-control, not to have just one more drink. And you're probably not even thinking about the hangover that awaits you tomorrow morning.