Blasphemously plagiaristic, and bombarding information.

“Trouble is, no creature who completely understands its role in the universe is talking.”
Robert Brault *www.robertbrault.com*

Just felt like being informative … verbatim. Why rephrase something that has been said so well? The following interested me and so I have relocated this information here from Wikipedia … Enjoy -

Psychoactive substances are used by humans for a number of different purposes. These uses vary widely between cultures. Some substances may have controlled or illegal uses while others may have shamanic purposes, and still others are used medicinally. Other examples would be social drinking or sleep aids. Caffeine is the world’s most widely consumed psychoactive substance, but unlike many others, it is legal and unregulated in nearly all jurisdictions. In North America, 90% of adults consume caffeine daily.[7]
Psychoactive drugs are divided into 3 groups:[1]
* Depressants – those that slow down the central nervous system; such as tranquilizers, alcohol, heroin and other opiates, cannabis (in low doses)
* Stimulants- those that excite the nervous system; such as nicotine, amphetamines, cocaine, caffeine
* Hallucinogens – those that alter how reality is perceived; such as LSD, mescaline, Psilocybin mushrooms, Salvia divinorum.

Recreational use
Many psychoactive substances are used for their mood and perception altering effects, including those with accepted uses in medicine and psychiatry. Examples include caffeine, alcohol, cocaine, LSD, and cannabis.[13] Classes of drugs frequently used recreationally include:
* Stimulants, which activate the central nervous system. These are used recreationally for their euphoric effects.
* Hallucinogens (psychedelics, dissociatives and deliriants), which induce perceptual and cognitive distortions.
* Hypnotics, which depress the central nervous system. These are used recreationally because of their euphoric effects.
* Opioid Analgesics, which also depress the central nervous system. These are used recreationally because of their euphoric effects.
* Inhalants, in the forms of gas aerosols, or solvents, which are inhaled as a vapor because of their stupefying effects. Many inhalants also fall into the above categories (such as nitrous oxide which is also an analgesic).
In some modern and ancient cultures, drug usage is seen as a status symbol. Recreational drugs are seen as status symbols in settings such as at nightclubs and parties.[14] For example, in ancient Egypt, gods were commonly pictured holding hallucinogenic plants.[15]
Because there is controversy about regulation of recreational drugs, there is an ongoing debate about drug prohibition. Critics of prohibition believe that regulation of recreational drug use is a violation of personal autonomy and freedom.[16] In the United States, critics have noted that prohibition or regulation of recreational and spiritual drug use might be unconstitutional.[17]

AH FORBID we have unconstitutional things happen in this world, in this day, in this age! For everything is already perfect and we are at peace with one another, and no one dies for illegitimate reasons EVER.
And sarcasm is so easy to convey without emoticons, who’d've thought.

Each drug has a specific action on one or more neurotransmitter or neuroreceptor in the brain.
Drugs that increase activity in particular neurotransmitter systems are called agonists. They act by increasing the synthesis of one or more neurotransmitters or reducing its reuptake from the synapses. Drugs that reduce neurotransmitter activity are called antagonists, and operate by interfering with synthesis or blocking postsynaptic receptors so that neurotransmitters cannot bind to them.[24]
Exposure to a psychoactive substance can cause changes in the structure and functioning of neurons, as the nervous system tries to re-establish the homeostasis disrupted by the presence of the drug. Exposure to antagonists for a particular neurotransmitter increases the number of receptors for that neurotransmitter, and the receptors themselves become more sensitive. This is called sensitization.
Conversely, over-stimulation of receptors for a particular neurotransmitter causes a decrease in both number and sensitivity of these receptors, a process called desensitization or tolerance. Sensitization and desensitization are more likely to occur with long-term exposure, although they may occur after only a single exposure. These processes are thought to underlie addiction.[25]

Uhm … that’s it. Just thought you should know :)

For those interested, my multiple extractions above came from the following article:

http://en.wikipedia.org/wiki/Psychoactive_drug