Psychoactive drug

Psychoactive_Drugs_Legend.jpg: 1. Cocaine

2. Crack cocaine

3. Methylphenidate (Ritalin)

4. Ephedrine

5. MDMA (ecstasy)

6. Peyote (mescaline)

7. LSD blotter

8. Psilocybin mushroom (Psilocybe cubensis)

9. Salvia divinorum (salvinorin A)

10. Diphenhydramine (Benadryl) (Unscheduled drug)

11. Amanita muscaria mushroom (muscimol)

12. Tylenol 3 (acetaminophen/codeine)

13. Codeine with muscle relaxant

14. Pipe tobacco (nicotine) (Unscheduled drug)

15. Bupropion (Unscheduled drug)

16. Cannabis (THC)

17. Hashish (THC)

18. ]]

A psychoactive drug, mind-altering drug, or consciousness-altering drug is a chemical substance that changes brain function and results in alterations in perception, mood, consciousness, cognition, or behavior. This category of drugs includes psychotropic drugs (a term often used interchangeably with psychoactive drug) and narcotic drugs. These substances may be used medically; recreationally; to purposefully improve performance or alter one's consciousness; as entheogens for ritual, spiritual, or shamanic purposes; or for research, including psychedelic therapy. Some categories of psychoactive drugs, which have therapeutic value, are prescribed by physicians and other healthcare practitioners. Examples include anesthetics, analgesics, anticonvulsant and antiparkinsonian drugs as well as medications used to treat neuropsychiatric disorders, such as antidepressants, anxiolytics, antipsychotics, and stimulant medications. Some psychoactive substances may be used in the detoxification and rehabilitation programs for persons dependent on or addicted to other psychoactive drugs.

Psychoactive substances often bring about subjective changes in consciousness and mood (although these may be objectively observed) that the user may find rewarding and pleasant (e.g., euphoria or a sense of relaxation) or advantageous in an objectively observable or measurable way (e.g. increased alertness), thus the effects are reinforcing to varying degrees. Substances which are rewarding and thus positively reinforcing have the potential to induce a state of addiction – compulsive drug use despite negative consequences. In addition, sustained use of some substances may produce physical or psychological dependence or both, associated with somatic or psychological-emotional withdrawal states respectively. Drug rehabilitation attempts to reduce addiction, through a combination of psychotherapy, support groups, and other psychoactive substances. Conversely, certain psychoactive drugs may be so unpleasant that the person will never use the substance again. This is especially true of certain deliriants (e.g. Jimson weed), powerful dissociatives (e.g. Salvia divinorum), and classic psychedelics (e.g. LSD, psilocybin), in the form of a "bad trip".

Psychoactive drug misuse, dependence, and addiction have resulted in legal measures and moral debate. Governmental controls on manufacture, supply, and prescription attempt to reduce problematic medical drug use; worldwide efforts to combat trafficking in psychoactive drugs are commonly termed the "war on drugs". Ethical concerns have also been raised about the overuse of these drugs clinically and about their marketing by manufacturers. Popular campaigns to decriminalize or legalize the recreational use of certain drugs (e.g., cannabis) are also ongoing.

History
Psychoactive drug use can be traced back to prehistory. There is archaeological evidence of the use of psychoactive substances, mostly plants, dating back at least 10,000 years and historical evidence of cultural use over the past 5,000 years. The chewing of coca leaves, for example, dates back over 8,000 years ago in Peruvian society.

Medicinal use is one important facet of psychoactive drug use. However, some have postulated the urge to alter one's consciousness as primary, as well as the drive to satiate thirst, hunger, or sexual desire. Supporters of this belief contend that the history of drug use, and even children's desire for spinning, swinging, or sliding indicate that the drive to alter one's state of mind is universal.

One of the first people to articulate this point of view, set aside from a medicinal context, was American author Fitz Hugh Ludlow (1836–1870) in his book The Hasheesh Eater (1857):"[D]rugs are able to bring humans into the neighborhood of divine experience and can thus carry us up from our personal fate and the everyday circumstances of our life into a higher form of reality. It is, however, necessary to understand precisely what is meant by the use of drugs. We do not mean the purely physical craving ... That of which we speak is something much higher, namely the knowledge of the possibility of the soul to enter into a lighter being, and to catch a glimpse of deeper insights and more magnificent visions of the beauty, truth, and the divine than we are normally able to spy through the cracks in our prison cell. But there are not many drugs which have the power of stilling such craving. The entire catalog, at least to the extent that research has thus far written it, may include only opium, hashish, and in rarer cases alcohol, which has enlightening effects only upon very particular characters."

During the 20th century, many governments across the world initially responded to the use of recreational drugs by banning use, production, or distribution of them, and making their use, supply, or trade a criminal offense. A notable example of this was Prohibition in the United States, where alcohol was made illegal for 13 years. However, many governments, government officials, and persons in law enforcement have concluded that illicit drug use cannot be sufficiently stopped through criminalization. Organizations such as Law Enforcement Against Prohibition (LEAP) have come to such a conclusion, believing: "[T]he existing drug policies have failed in their intended goals of addressing the problems of crime, drug abuse, addiction, juvenile drug use, stopping the flow of illegal drugs into this country and the internal sale and use of illegal drugs. By fighting a war on drugs the government has increased the problems of society and made them far worse. A system of regulation rather than prohibition is a less harmful, more ethical and a more effective public policy."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 adequate factual information readily available, and that the negative effects of their use be minimized. Such is the case of the Portuguese drug policy of decriminalization, which achieved its primary goal of reducing the adverse health effects of drug abuse.

Terminology
The term "drug" has become a skunked term; Drugs can have a negative connotation, often associated with illegal substances like cocaine or heroin. This is despite the fact that the terms "drug" and "medicine" are sometimes used interchangeably.

Novel psychoactive substances (NPS), also known as "designer drugs" are a category of psychoactive drugs (substances) that are designed to mimic the effects of often illegal drugs, usually in efforts to circumvent existing drug laws.

Types
Psychoactive drugs are divided according to their pharmacological effects. Common subtypes include:


 * Anxiolytics are medicinally used to reduce the symptoms of anxiety, and sometimes insomnia.
 * Example: benzodiazepines such as Xanax and Valium; barbiturates


 * Empathogen–entactogens alter one's emotional state, often resulting in an increased sense of empathy, closeness, and emotional communication.


 * Example: MDMA (ecstasy), MDA, 6-APB, AMT


 * Stimulants increase activity, or arousal, of the central nervous system, used to enhance alertness, attention, cognition, mood and physical performance. Some stimulants are used medicinally to treat individuals with ADHD and narcolepsy.
 * Examples: amphetamines, caffeine, cocaine, nicotine


 * Depressants reduce (or depress) activity and stimulation in the central nervous system. Drugs within this classification encompass a spectrum of substances with sedative, soporific, and anesthetic properties, and include sedatives, hypnotics, and opioids.


 * Examples: ethanol (alcohol), opioids such as morphine, fentanyl, and codeine, cannabis, barbiturates, and benzodiazepines


 * Hallucinogens, including psychedelics, dissociatives and deliriants, encompass substances that produce distinct alterations in perception, sensation of space and time, and emotional state.
 * Examples: psilocybin, LSD, DMT (N,N-Dimethyltryptamine), mescaline, Salvia divinorum, nitrous oxide, datura, scopolamine

Uses
Use of psychoactive substances vary widely between cultures. Some substances may have controlled or illegal uses, others may have shamanic purposes, and others are used medicinally. Examples would be social drinking, nootropic supplements, and sleep aids. Caffeine is the world's most widely consumed psychoactive substance: it is legal and unregulated in nearly all jurisdictions; in North America, 90% of adults consume caffeine daily.

Mental disorders


Psychiatric medications are psychoactive drugs prescribed for the management of mental and emotional disorders, or to aid in overcoming challenging behavior. There are six major classes of psychiatric medications:
 * Antidepressants treat disorders such as clinical depression, dysthymia, anxiety, eating disorders, and borderline personality disorder.
 * Stimulants, used to treat disorders such as attention deficit hyperactivity disorder and narcolepsy, and for weight reduction.
 * Antipsychotics, used to treat psychotic symptoms, such as those associated with schizophrenia or severe mania, or as adjuncts to relieve clinical depression.
 * Mood stabilizers, used to treat bipolar disorder and schizoaffective disorder.
 * Anxiolytics, used to treat anxiety disorders.
 * Depressants, used as hypnotics, sedatives, and anesthetics, depending upon dosage.

In addition, several psychoactive substances are currently employed to treat various addictions. These include acamprosate or naltrexone in the treatment of alcoholism, or methadone or buprenorphine maintenance therapy in the case of opioid addiction.

Exposure to psychoactive drugs can cause changes to the brain that counteract or augment some of their effects; these changes may be beneficial or harmful. However, there is a significant amount of evidence that the relapse rate of mental disorders negatively corresponds with the length of properly followed treatment regimens (that is, relapse rate substantially declines over time), and to a much greater degree than placebo.

Drugs used by militaries
Both military and civilian American intelligence officials are known to have used psychoactive drugs while interrogating captives apprehended in its "war on terror". In July 2012 Jason Leopold and Jeffrey Kaye, psychologists and human rights workers, had a Freedom of Information Act request fulfilled that confirmed that the use of psychoactive drugs during interrogation was a long-standing practice. Captives and former captives had been reporting medical staff collaborating with interrogators to drug captives with powerful psychoactive drugs prior to interrogation since the very first captives release. In May 2003 recently released Pakistani captive Sha Mohammed Alikhel described the routine use of psychoactive drugs. He said that Jihan Wali, a captive kept in a nearby cell, was rendered catatonic through the use of these drugs.

Additionally, militaries worldwide have used or are using various psychoactive drugs to improve performance of soldiers by suppressing hunger, increasing the ability to sustain effort without food, increasing and lengthening wakefulness and concentration, suppressing fear, reducing empathy, and improving reflexes and memory-recall among other things.

The first documented case of a soldier overdosing on methamphetamine during combat, was the Finnish corporal Aimo Koivunen, a soldier who fought in the Winter War and the Continuation War.

Psychochemical warfare
Psychoactive drugs have been used in military applications as non-lethal weapons.

Pain management
Psychoactive drugs are often prescribed to manage pain. The subjective experience of pain is primarily regulated by endogenous opioid peptides. Thus, pain can often be managed using psychoactives that operate on this neurotransmitter system, also known as opioid receptor agonists. This class of drugs can be highly addictive, and includes opiate narcotics, like morphine and codeine. NSAIDs, such as aspirin and ibuprofen, are also analgesics. These agents also reduce eicosanoid-mediated inflammation by inhibiting the enzyme cyclooxygenase.

Anesthesia
General anesthetics are a class of psychoactive drug used on people to block physical pain and other sensations. Most anesthetics induce unconsciousness, allowing the person to undergo medical procedures like surgery, without the feelings of physical pain or emotional trauma. To induce unconsciousness, anesthetics affect the GABA and NMDA systems. For example, Propofol is a GABA agonist, and ketamine is an NMDA receptor antagonist.

Performance-enhancement
Performance-enhancing substances, also known as performance-enhancing drugs (PEDs), are substances that are used to improve any form of activity performance in humans. A well-known example of cheating in sports involves doping in sport, where banned physical performance-enhancing drugs are used by athletes and bodybuilders. Athletic performance-enhancing substances are sometimes referred as ergogenic aids. Cognitive performance-enhancing drugs, commonly called nootropics, are sometimes used by students to improve academic performance. Performance-enhancing substances are also used by military personnel to enhance combat performance.

Recreation
Many psychoactive substances are used for their mood and perception altering effects, including those with accepted uses in medicine and psychiatry. Examples of psychoactive substances include caffeine, alcohol, cocaine, LSD, nicotine and cannabis. 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 alterations.
 * Hypnotics, which depress the central nervous system.
 * 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. For example, in ancient Egypt, gods were commonly pictured holding hallucinogenic plants.

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. In the United States, critics have noted that prohibition or regulation of recreational and spiritual drug use might be unconstitutional, and causing more harm than is prevented.

Some people who take psychoactive drugs experience drug or substance induced psychosis. A 2019 systematic review and meta-analysis by Murrie et al. found that the pooled proportion of transition from substance-induced psychosis to schizophrenia was 25% (95% CI 18%–35%), compared with 36% (95% CI 30%–43%) for brief, atypical and not otherwise specified psychoses. Type of substance was the primary predictor of transition from drug-induced psychosis to schizophrenia, with highest rates associated with cannabis (6 studies, 34%, CI 25%–46%), hallucinogens (3 studies, 26%, CI 14%–43%) and amphetamines (5 studies, 22%, CI 14%–34%). Lower rates were reported for opioid (12%), alcohol (10%) and sedative (9%) induced psychoses. Transition rates were slightly lower in older cohorts but were not affected by sex, country of the study, hospital or community location, urban or rural setting, diagnostic methods, or duration of follow-up.

Alcohol
According to the Catholic Church, the sacramental wine used in the Eucharist must contain alcohol. Canon 924 of the present Code of Canon Law (1983) states: §3 The wine must be natural, made from grapes of the vine, and not corrupt.

Entheogen


Certain psychoactives, particularly hallucinogens, have been used for religious purposes since prehistoric times. Native Americans have used peyote cacti containing mescaline for religious ceremonies for as long as 5700 years. The muscimol-containing Amanita muscaria mushroom was used for ritual purposes throughout prehistoric Europe.

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 spiritual and intention-based movements began to use LSD and other hallucinogens as tools to access deeper inner exploration. 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.

Psychedelic therapy
Psychedelic therapy (or psychedelic-assisted therapy) refers to the proposed use of psychedelic drugs, such as psilocybin, MDMA, LSD, and ayahuasca, to treat mental disorders. As of 2021, psychedelic drugs are controlled substances in most countries and psychedelic therapy is not legally available outside clinical trials, with some exceptions.

Psychonautics
The aims and methods of psychonautics, when state-altering substances are involved, is commonly distinguished from recreational drug use by research sources. Psychonautics as a means of exploration need not involve drugs, and may take place in a religious context with an established history. Cohen considers psychonautics closer in association to wisdom traditions and other transpersonal and integral movements.

Self-medication
Self-medication, sometime called do-it-yourself (DIY) medicine, is a human behavior in which an individual uses a substance or any exogenous influence to self-administer treatment for physical or psychological conditions, for example headaches or fatigue.

The substances most widely used in self-medication are over-the-counter drugs and dietary supplements, which are used to treat common health issues at home. These do not require a doctor's prescription to obtain and, in some countries, are available in supermarkets and convenience stores.

Sex
Sex and drugs date back to ancient humans and have been interlocked throughout human history. Both legal and illegal, the consumption of drugs and their effects on the human body encompasses all aspects of sex, including desire, performance, pleasure, conception, gestation, and disease.

There are many different types of drugs that are commonly associated with their effects on sex, including alcohol, cannabis, cocaine, MDMA, GHB, amphetamines, opioids, antidepressants, and many others.

Operation Overgrow
Operation Overgrow is the name, given by cannabis activists, of an "operation" to spread marijuana seeds wildly "so it grows like weed". The thought behind the operation is to draw attention to the debate about legalization/decriminalization of marijuana.

Suicide
A drug overdose involves taking a dose of a drug that exceeds safe levels. In the UK (England and Wales) until 2013, a drug overdose was the most common suicide method in females. In 2019 in males the percentage is 16%. Self-poisoning accounts for the highest number of non-fatal suicide attempts. In the United States about 60% of suicide attempts and 14% of suicide deaths involve drug overdoses. The risk of death in suicide attempts involving overdose is about 2%.

Most people are under the influence of sedative-hypnotic drugs (such as alcohol or benzodiazepines) when they die by suicide, with alcoholism present in between 15% and 61% of cases. Countries that have higher rates of alcohol use and a greater density of bars generally also have higher rates of suicide. About 2.2–3.4% of those who have been treated for alcoholism at some point in their life die by suicide. Alcoholics who attempt suicide are usually male, older, and have tried to take their own lives in the past. In adolescents who misuse alcohol, neurological and psychological dysfunctions may contribute to the increased risk of suicide.

Overdose attempts using painkillers are among the most common, due to their easy availability over-the-counter.

Route of administration
Psychoactive drugs are administered via oral ingestion as a tablet, capsule, powder, liquid, and beverage; via injection by subcutaneous, intramuscular, and intravenous route; via rectum by suppository and enema; and via inhalation by smoking, vaporizing, and snorting. The efficiency of each method of administration varies from drug to drug.

The psychiatric drugs fluoxetine, quetiapine, and lorazepam are ingested orally in tablet or capsule form. Alcohol and caffeine are ingested in beverage form; nicotine and cannabis are smoked or vaporized; peyote and psilocybin mushrooms are ingested in botanical form or dried; and crystalline drugs such as cocaine and methamphetamine are usually inhaled or snorted.

Determinants of effects
The theory of dosage, set, and setting is a useful model in dealing with the effects of psychoactive substances, especially in a controlled therapeutic setting as well as in recreational use. Dr. Timothy Leary, based on his own experiences and systematic observations on psychedelics, developed this theory along with his colleagues Ralph Metzner, and Richard Alpert (Ram Dass) in the 1960s.

The first factor, dosage, has been a truism since ancient times, or at least since Paracelsus who said, "Dose makes the poison." Some compounds are beneficial or pleasurable when consumed in small amounts, but harmful, deadly, or evoke discomfort in higher doses.
 * Dosage

The set is the internal attitudes and constitution of the person, including their expectations, wishes, fears, and sensitivity to the drug. This factor is especially important for the hallucinogens, which have the ability to make conscious experiences out of the unconscious. In traditional cultures, set is shaped primarily by the worldview, health and genetic characteristics that all the members of the culture share.
 * Set

The third aspect is setting, which pertains to the surroundings, the place, and the time in which the experiences transpire.
 * Setting

This theory clearly states that the effects are equally the result of chemical, pharmacological, psychological, and physical influences. The model that Timothy Leary proposed applied to the psychedelics, although it also applies to other psychoactives.

Effects


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, by reducing its reuptake from the synapses, or by mimicking the action by binding directly to the postsynaptic receptor. 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.

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 (see also, neuroplasticity). Exposure to antagonists for a particular neurotransmitter can increase the number of receptors for that neurotransmitter or the receptors themselves may become more responsive to neurotransmitters; this is called sensitization. Conversely, overstimulation of receptors for a particular neurotransmitter may cause 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 play a role in drug dependence and addiction. Physical dependence on antidepressants or anxiolytics may result in worse depression or anxiety, respectively, as withdrawal symptoms. Unfortunately, because clinical depression (also called major depressive disorder) is often referred to simply as depression, antidepressants are often requested by and prescribed for patients who are depressed, but not clinically depressed.

Affected neurotransmitter systems
The following is a brief table of notable drugs and their primary neurotransmitter, receptor or method of action. Many drugs act on more than one transmitter or receptor in the brain.

Addiction and dependence


Psychoactive drugs are often associated with addiction or drug dependence. Dependence can be divided into two types: psychological dependence, by which a user experiences negative psychological or emotional withdrawal symptoms (e.g., depression) and physical dependence, by which a user must use a drug to avoid physically uncomfortable or even medically harmful physical withdrawal symptoms. Drugs that are both rewarding and reinforcing are addictive; these properties of a drug are mediated through activation of the mesolimbic dopamine pathway, particularly the nucleus accumbens. Not all addictive drugs are associated with physical dependence, e.g., amphetamine, and not all drugs that produce physical dependence are addictive drugs, e.g., oxymetazoline.

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.

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, as is another opioid, buprenorphine. Recent research on addiction has shown some promise in using psychedelics such as ibogaine to treat and even cure drug addictions, although this has yet to become a widely accepted practice.

Legality


The legality of psychoactive drugs has been controversial through most of recent history; the Second Opium War 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, Pakistan, 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. 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.

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. 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. Alcohol is regulated by state governments, but the federal National Minimum Drinking Age Act penalizes states for not following a national drinking age. Tobacco is also regulated by all fifty state governments. Most people accept such restrictions and prohibitions of certain drugs, especially the "hard" drugs, which are illegal in most countries.

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.

Effect on animals
A number of animals consume different psychoactive plants, animals, berries and even fermented fruit, becoming intoxicated. An example of this is cats after consuming catnip. Traditional legends of sacred plants often contain references to animals that introduced humankind to their use. Animals and psychoactive plants appear to have co-evolved, possibly explaining why these chemicals and their receptors exist within the nervous system.

Widely used psychoactive drugs
This is a list of commonly used drugs that contain psychoactive ingredients. Please note that the following lists contains legal and illegal drugs (based on the country's laws).

Common legal drugs
The most widely consumed psychotropic drugs worldwide are:
 * Alcohol
 * Caffeine
 * Nicotine

Common prescribed drugs

 * Benzodiazepines
 * Cannabis
 * Opioids

Common street drugs
• Cocaine

• Heroin

• LSD

• Methamphetamine

• Ecstasy

• Psilocybin mushrooms