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Main article: Drugs

An assortment of psychoactive drugs

A psychoactive drug or psychotropic substance is a chemical substance that acts primarily upon the central nervous system where it alters brain function, resulting in temporary changes in perception, mood, consciousness and behaviour. These drugs may be used recreationally to purposefully alter one's consciousness, as entheogens for ritual or spiritual purposes, as a tool for studying or augmenting the mind, or therapeutically as medication.

Because psychoactive substances bring about subjective changes in consciousness and mood that the user may find pleasant (e.g. euphoria) or advantageous (e.g. increased alertness), many psychoactive substances are abused, that is, used excessively, despite risks or negative consequences. With sustained use of some substances, physical dependence may develop, making the cycle of abuse even more difficult to interrupt. Drug rehabilitation can involve a combination of psychotherapy, support groups and even other psychoactive substances to break the cycle of dependency.

In part because of this potential for abuse and dependency, the ethics of drug use are the subject of a continuing philosophical debate. Many governments worldwide have placed restrictions on drug production and sales in an attempt to decrease drug abuse.


Drug use is a practice that dates to prehistoric times. There is archaeological evidence of the use of psychoactive substances dating back at least 10,000 years, and historical evidence of cultural use over the past 5,000 years.[1] While medicinal use seems to have played a very large role, it has been suggested that the urge to alter one's consciousness is as primary as the drive to satiate thirst, hunger or sexual desire.[2] Others suggest that marketing, availability or the pressures of modern life are why humans use so many psychoactives in their daily lives. However, the long history of drug use and even children's desire for spinning, swinging, or sliding indicates that the drive to alter one's state of mind is universal.[3]

This relationship is not limited to humans. A number of animals consume different psychoactive plants, animals, berries and even fermented fruit, becoming intoxicated, such as cats after consuming catnip. Traditional legends of sacred plants often contain references to animals that introduced humankind to their use.[4] Biology suggests an evolutionary connection between psychoactive plants and animals, as to why these chemicals and their receptors exist within the nervous system.[5]

During the 20th century, many governments across the world initially responded to the use of recreational drugs by banning them and making their use, supply or trade a criminal offense. A notable example of this is the Prohibition era in the United States, where alcohol was made illegal for 13 years. However, many governments have concluded that illicit drug use cannot be sufficiently stopped through criminalization. In some countries, there has been a move toward harm reduction by health services, where the use of illicit drugs is neither condoned nor promoted, but services and support are provided to ensure users have the negative effects of their illicit drug use minimized.[How to reference and link to summary or text] This can go hand-in-hand with supply reduction strategies by law-enforcement agencies.

Uses of psychoactive substances

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.[6]


Main article: Anesthesia

General anesthetics are a class of psychoactive drug used on patients to block pain and other sensations. Most anesthetics induce unconsciousness, which allows patients to undergo medical procedures like surgery without physical pain or emotional trauma.[7] To induce unconsciousness, anesthetics affect the GABA and NMDA systems. For example, halothane is a GABA agonist,[8] and ketamine is an NMDA receptor antagonist.[9]


Main article: Analgesics


Psychoactive drugs are often prescribed to manage pain. As the subjective experience of pain is regulated by endorphins, neurochemicals that are endogenous opioids, pain can be managed using psychoactives that operate on this neurotransmitter system. This class of drugs includes narcotics, like morphine and codeine,[10] and also NSAIDs (which don't affect endorphins) such as aspirin and ibuprofen.

Psychiatric medications

Main article: Psychiatric medications

Zoloft, an antidepressant (and anti-anxiety) medication

Psychiatric medications are prescribed for the management of mental and emotional disorders. There are 6 major classes of psychiatric medications:

Recreational drugs

Main article: Recreational drug use

Many psychoactive substances are used for their mood and perception altering effects, including those with accepted uses in medicine and psychiatry. Classes of drugs frequently used recreationally include:

  • Stimulants, which elevate 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 are used recreationally because they induce inebriation.
  • Analgesics, which 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 anelgesic)

Examples include caffeine, alcohol, cocaine, LSD, and cannabis.[12]

In some sub-cultures, drug usage is seen as a status symbol. Recreational drugs are seen as status symbols at events such as at nightclubs and parties.[13] This is true of many cultures throughout history; drugs have been viewed as status symbols since ancient times. For example, in ancient Egypt, gods were commonly pictured holding hallucinogenic plants.[14]

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.[15] In the United States, critics have noted that prohibition or regulation of recreational and spiritual drug use might be unconstitutional.[16]

Ritual and spiritual use


Timothy Leary was a leading proponent of spiritual hallucinogen use.

Main article: Entheogens

Certain psychoactives, particularly hallucinogens, have been used for religious purposes since prehistoric times. Native Americans have used mescaline-containing peyote cacti for religious ceremonies for as long as 5700 years.[17] The muscimol-containing Amanita muscaria mushroom was used for ritual purposes throughout prehistoric Europe.[18] Various other hallucinogens, including jimsonweed, psilocybin mushrooms, and cannabis have been used in religious ceremonies for centuries.[19]

The use of entheogens for religious purposes resurfaced in the West during the counterculture movements of the 1960s and 70s. Under the leadership of Timothy Leary, new religious movements began to use LSD and other hallucinogens as sacraments.[20] In the United States, the use of peyote for ritual purposes is protected only for members of the Native American Church, which is allowed to cultivate and distribute peyote. However, the genuine religious use of Peyote, regardless of one's personal ancestry, is protected in Colorado, Arizona, New Mexico, Nevada, and Oregon.[21]


For a substance to be psychoactive, it must cross the blood-brain barrier so it can affect neurochemical function. Psychoactive drugs are administered in several different ways. In medicine, most psychiatric drugs, such as fluoxetine, quetiapine, and lorazepam are ingested orally in tablet or capsule form. However, certain medical psychoactives are administered via inhalation, injection, or rectal suppository/enema. Recreational drugs can be administered in several additional ways that are not common in medicine. Certain drugs, such as alcohol and caffeine, are ingested in beverage form; nicotine and cannabis are often smoked; peyote and psilocybin mushrooms are ingested in botanical form or dried; and certain crystalline drugs such as cocaine and methamphetamines are often insufflated. The efficiency of each method of administration varies from drug to drug.[22]


File:Synapse Illustration2 tweaked.svg

Illustration of the major elements of neurotransmission. Depending on its method of action, a psychoactive substance may block the receptors on the post-synaptic neuron (dendrite), or block reuptake or affect neurotransmitter synthesis in the pre-synaptic neuron (axon).

Main article: Neuropsychopharmacology

Psychoactive drugs operate by temporarily affecting a person's neurochemistry, which in turn causes changes in a person's mood, cognition, perception and behavior. There are many ways in which psychoactive drugs can affect the brain. 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.[23]

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, overstimulation 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.[24]

Affected neurotransmitter systems

The following is a brief table of notable drugs and their primary neurotransmitter, receptor or method of action. It should be noted that many drugs act on more than one transmitter or receptor in the brain.[25]

Neurotransmitter/receptor Classification Examples

Cholinergics (acetylcholine agonists) nicotine, piracetam
Anticholinergics (acetylcholine antagonists) scopolamine, dimenhydrinate, diphenhydramine, atropine, most tricyclics
Adenosine receptor antagonists[26] caffeine, theobromine, theophylline

Dopamine reuptake inhibitors (DRIs) cocaine, methylphenidate, amphetamine, bupropion
Dopamine releasers amphetamine
Dopamine agonists pramipexole, L-DOPA (prodrug)
Dopamine receptor antagonists haloperidol, droperidol, many antipsychotics

File:Gamma-Aminobuttersäure - gamma-aminobutyric acid.svg

GABA reuptake inhibitors tiagabine
GABA receptor agonists ethanol, barbiturates, diazepam and other benzodiazepines, muscimol, ibotenic acid
GABA antagonists thujone, bicuculline
Noradrenaline chemical structure.png

Norepinephrine reuptake inhibitors most non-SSRI antidepressants such as amoxapine, atomoxetine, bupropion, venlafaxine and the tricyclics
Norepinephrine releasers mianserin
Serotonin receptor agonists LSD, psilocybin, mescaline, DMT
Serotonin reuptake inhibitors most antidepressants including tricyclics such as amitryptyline and SSRIs such as fluoxetine and sertraline
Serotonin releasers MDMA (ecstasy)
AMPA receptor
AMPA receptor antagonists kynurenic acid, NBQX
Cannabinoid receptor
Cannabinoid receptor agonists THC
Melanocortin receptor
Melanocortin receptor agonists bremelanotide
NMDA receptor
NMDA receptor antagonists ketamine, PCP, DXM
Opioid receptor
μ-opioid receptor agonists morphine, heroin, oxycodone
μ-opioid receptor inverse agonists naloxone, naltrexone
κ-opioid receptor agonists salvinorin A, butorphanol, nalbuphine
κ-opioid receptor inverse agonists buprenorphine
Monoamine oxidase
Monoamine oxidase inhibitors (MAOIs) phenelzine, iproniazid
bind to MAO protein transporter amphetamine, methamphetamine


Main article: Addiction

Heroin bottle

Psychoactive drugs are often associated with addiction. Addiction can be divided into two types: psychological addiction, by which a user feels compelled to use a drug despite negative physical or societal consequence, and physical dependence, by which a user must use a drug to avoid medically harmful withdrawal.[27] Not all drugs are physically addictive, but any activity that stimulates the brain's dopaminergic reward system — typically, any pleasurable activity[28] — can lead to psychological addiction.[27] Drugs that are most likely to cause addiction are drugs that directly stimulate the dopaminergic system, like cocaine and amphetamines. Drugs that only indirectly stimulate the dopaminergic system, such as psychedelics, are not as likely to be addictive.

Many professionals, self-help groups, and businesses specialize in drug rehabilitation, with varying degrees of success, and many parents attempt to influence the actions and choices of their children regarding psychoactives.[29]

Common forms of rehabilitation include psychotherapy, support groups and pharmacotherapy, which uses psychoactive substances to reduce cravings and physiological withdrawal symptoms while a user is going through detox. Methadone, itself an opioid and a psychoactive substance, is a common treatment for heroin addiction. Recent research on addiction has shown some promise in using psychedelics to treat and even cure addictions, although this has yet to become a widely accepted practice.[30][31]


The legality of psychoactive drugs has been controversial through most of recent history; the Opium Wars and Prohibition are two historical examples of legal controversy surrounding psychoactive drugs. However, in recent years, the most influential document regarding the legality of psychoactive drugs is the Single Convention on Narcotic Drugs, an international treaty signed in 1961 as an Act of the United Nations. Signed by 73 nations including the United States, the USSR, India, and the United Kingdom, the Single Convention on Narcotic Drugs established Schedules for the legality of each drug and laid out an international agreement to fight addiction to recreational drugs by combatting the sale, trafficking, and use of scheduled drugs.[32] All countries that signed the treaty passed laws to implement these rules within their borders. However, some countries that signed the Single Convention on Narcotic Drugs, such as the Netherlands, are more lenient with their enforcement of these laws.[33]

In the United States, the Food and Drug Administration (FDA) has authority over all drugs, including psychoactive drugs. The FDA regulates which psychoactive drugs are over the counter and which are only available with a prescription.[34] However, certain psychoactive drugs, like alcohol, tobacco, and drugs listed in the Single Convention on Narcotic Drugs are subject to criminal laws. The Controlled Substances Act of 1970 regulates the recreational drugs outlined in the Single Convention on Narcotic Drugs.[35] Alcohol is regulated by state governments, but the federal National Minimum Drinking Age Act penalizes states for not following a national drinking age.[36] Tobacco is also regulated by all fifty state governments.[37] Most people accept such restrictions and prohibitions of certain drugs, especially the "hard" drugs, which are illegal in most countries.[38][39][40]

At the beginning of the 21st century, legally prescribed illegal psychoactive drugs used for legitimate purposes have been targeted by the US Justice System.[41]

In the medical context, psychoactive drugs as a treatment for illness is widespread and generally accepted. Little controversy exists concerning over the counter psychoactive medications in antiemetics and antitussives. Psychoactive drugs are commonly prescribed to patients with psychiatric disorders. However, certain critics believe that certain prescription psychoactives, such as antidepressants and stimulants, are overprescribed and threaten patients' judgement and autonomy.[42][43]

See also


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