Cocaine is a local anesthetic
and in the brain is a stimulant
. It is commonly used for illegal recreational purposes and occasionally used by doctors for surgery.
Users typically report a huge mind and body rush, clarity of thought and the general feeling of being "Superman". After they come down they often feel depression, anxiety and a huge desire to do more.
The function is primarily through blocking dopamine and less so, serotonin re-uptake, (a number of other neurotransmitters are also affected, but they are relativity insignificant compared to these two) causing the neurotransmitter to stay in the synapse longer than normal.
The function of dopamine in the brain is primarily to re-enforce an action that one takes. Not necessarily a positive kind of reinforcement. This is the reason people think that having "just one more line" will solve their problems. It does, for roughly 15 minutes, then they crash again. People can be addicted to dopamine release without actually enjoying the release. It also has a number of other roles including mood and aggression. The primary component of a cocaine high is the dopamine release. It is also greatly responsible for telling yourself that you have the ability to do things. This is why people can get delusional into thinking they can do the impossible on cocaine. It is a huge ego boost.
Serotonin is responsible for inhibiting aggression, is included in a large part of perception and mood. Antidepressants are generally serotonin uptake blockers. MDMA releases a whole lot of serotonin at once elevating mood. Cocaine releases some as well, instilling a sense of calm.
The powder can be converted into a smokable form. (either freebase or crack, there are slight differences) This method is more prone to overdose due to the chemical almost instantly going to the brain. Also in the case of creating a freebase an explosion is quite likely.
A fatal overdose of cocaine is usually not from the actions in the brain but rather the effect on the respiratory system, since the body uses the same neurotransmitter in the body as the brain only for different functions.
It is most commonly sniffed in lines but it is occasionally injested orally or injected into the bloodstream. When sniffed effects begin within a couple of minutes and last between a half hour and an hour. When ingested orally the effects are more mild and onset can take up to an hour.