Addiction is an uncontrollable compulsion to repeat a behavior regardless of its negative consequences. A person who is addicted is sometimes called an addict.

Many drugs or behaviors can precipitate a pattern of conditions recognized as addiction, which include a craving for more of the drug or behavior, increased physiological tolerance to exposure, and withdrawal symptoms in the absence of the stimulus. Most drugs and behaviors that directly provide either pleasure or relief from pain pose a risk of dependency. Addictions can also be formed due to opponent process reactions. For example the terror of jumping out of an airplane is rewarded with intense pleasure when the parachute opens. Because of opponent process criminal behavior, running, stealing, violence, acting, test taking can become habit forming.

Varied forms of addiction

The medical community now carefully distinguishes between physical dependence (withdrawals) and psychological addiction (or simply addiction). Addiction is now narrowly defined as "uncontrolled, compulsive use despite harm"; if there is no harm to the patient or another party, there is no addiction. The obsolete term physical addiction is deprecated because of its pejorative connotations, especially in modern pain management with opioids where physical dependence is nearly universal but addiction is rare.

Physical dependency on a substance is defined by the appearance of characteristic withdrawal symptoms when the drug is suddenly discontinued. While opioids, benzodiazepines, barbiturates, alcohol and nicotine are all well known for their ability to induce physical dependence, other drugs share this property that are not considered addictive: cortisone, beta-blockers and most antidepressants are examples. Also, some highly addictive drugs, such as cocaine, induce relatively little physical dependence. So while physical dependency can be a major factor in the psychology of addiction, the primary attribute of an addictive drug is its ability to induce euphoria while causing harm.

Some drugs induce physical dependence or physiological tolerance - but not addiction - for example many laxatives, which are not psychoactive; nasal decongestants, which can cause rebound congestion if used for more than a few days in a row; and some antidepressants, most notably Effexor and Paxil, as they have quite short half-lives, so stopping them abruptly causes a more rapid change in the neurotransmitter balance in the brain than many other antidepressants. Many non-addictive prescription drugs should not be suddenly stopped, so a doctor should be consulted before abruptly discontinuing them.

Psychological addictions are a dependency of the mind, and lead to psychological withdrawal symptoms. Addictions can theoretically form for any rewarding behavior, but typically only do so in individuals with emotional, social, or psychological dysfunctions, taking the place of normal positive stimuli not otherwise attained (see Rat Park). The distinction between the two kinds of addictions, however, is not always easy to make. Addictions often have both physical and psychological components.

There is also a lesser known situation called pseudo-addiction, where a patient will exhibit drug seeking behaviour reminiscent of psychological addiction, however in this case, the patients tend to have genuine pain or other symptoms that have been undertreated. Unlike true psychological addiction, however, these behaviours tend to stop as soon as their pain is adequately treated.

Not all doctors do agree on what addiction or dependency is. However, researchers, doctors, and popular literature discuss many addictions, including those to alcohol, tobacco, drugs, gambling, food, and even sex, pornography, computers and work.

While eating disorders, like other behavioral addictions, are usually considered primarily psychological disorders, they are sometimes treated as addictions, especially if they include elements of addictive behavior. Sufferers may experience withdrawal or withdrawal-like symptoms if they alter their diet suddenly. This suggests that some common food substances, especially chocolate, caffeine, and sugar, may have the potential for addiction.

The speed with which a given individual becomes addicted to various substances varies with the substance, the frequency of use, the means of ingestion, and the individual. Some alcoholics report they exhibited alcoholic tendencies from the moment of first intoxication, while most people can drink socially without ever becoming addicted. Nicotine is considered by many to be the most addictive substance in the world.

Methods of care

Early editions of the American Psychiatric Association's Diagnostic and Statistical Manual of Mental Disorders described addiction as a physical dependency to a substance that resulted in withdrawal symptoms in its absence. Recent editions, including DSM-IV, have moved toward a diagnostic instrument that classifies such conditions as dependency, rather than addiction. The American Society of Addiction Medicine recommends treatment for people with chemical dependency based on patient placement criteria (currently listed in PPC-2), which attempt to match levels of care according to clinical assessments in six areas, including:

• Acute intoxication and/or withdrawal potential
• Biomedical conditions or complications
• Emotional/behavioral conditions or complications
• Treatment acceptance/resistance
• Relapse potential
• Recovery environment

Some medical systems, including those of at least 15 states of the United States, refer to an Addiction Severity Index to assess the severity of problems related to substance use. The index assesses problems in six areas: medical, employment/support, alcohol and other drug use, legal, family/social, and psychiatric.

While addiction or dependency is related to seemingly uncontrollable urges, and may have roots in genetic predisposition, treatment of dependency is always classified as behavioral medicine. Early treatment of acute withdrawal often includes medical detoxification, which can include doses of anxiolytics to reduce symptoms of withdrawal. In chronic opiate addiction, a surrogate drug such as methadone is sometimes offered as a form of opiate replacement therapy. But treatment approaches universally focus on the individual's ultimate choice to pursue an alternate course of action.

Therapists often classify patients with chemical dependencies as either interested or not interested in changing. Treatments usually involve planning for specific ways to avoid the addictive stimulus, and therapeutic interventions intended to help a client learn healthier ways to find satisfaction. Clinical leaders in recent years have attempted to tailor intervention approaches to specific influences that effect addictive behavior, using therapeutic interviews in an effort to discover factors that led a person to embrace unhealthy, addictive sources of pleasure or relief from pain.

Treatment Modality Matrix
Behavioral Pattern	Intervention	Goals
Low self esteem, anxiety, verbal hostility	Relationship therapy, client centered approach	Increase self esteem, reduce hostility and anxiety
Defective personal constructs, ignorance of interpersonal means	Cognitive restructuring including directive and group therapies	Insight
Focal anxiety such as fear of crowds	Desensitization	Change response to same cue
Undesirable behaviors, lacking appropriate behaviors	Aversive conditioning, operant conditioning, counter conditioning	Eliminate or replace behavior
Lack of information	Provide information	Have client act on information
Difficult social circumstances	Organizational intervention, environmental manipulation, family counseling	Remove cause of social difficulty
Poor social performance, rigid interpersonal behavior	Sensitivity training, communication training, group therapy	Increase interpersonal repertoire, desensitization to group functioning
Grossly bizarre behavior	Medical referral	Protect from society, prepare for further treatment
Adapted from: Essentials of Clinical Dependency Counseling, Aspen Publishers

Diverse explanations

Several explanations (or "models") have been presented to explain addiction:

• The moral model states that addictions are the result of human weakness, and are defects of character. Those who advance this model do not accept that there is any biological basis for addiction. They often have scant sympathy for people with serious addictions, believing either that a person with greater moral strength could have the force of will to break an addiction, or that the addict demonstrated a great moral failure in the first place by starting the addiction. The moral model is widely applied to dependency on illegal substances, perhaps purely for social or political reasons, but is no longer widely considered to have any therapeutic value. Elements of the moral model, especially a focus on individual choices, have found enduring roles in other approaches to the treatment of dependencies.

• The opponent-process model generated by Richard Soloman states that for every psychological event A will be followed by its opposite psychological event B. For example the pleasure one experiences from heroin is followed by an opponent process of withdrawal. This model is related to the opponent process color theory. If you look at the color red then quickly look at a gray area you will see green. There are many examples of opponent processes in the nervous system including taste, motor movement, touch, vision, and hearing.

• The disease model holds that addiction is an illness, and comes about as a result of the impairment of healthy neurochemical or behavioral processes. While there is some dispute among clinicians as to the reliability of this model, it is widely employed in therapeutic settings. Most treatment approaches involve recognition that dependencies are behavioral dysfunctions, and thus involve some element of physical or mental disease.

• The genetic model posits a genetic predisposition to certain behaviors. It is frequently noted that certain addictions "run in the family," and while researchers continue to explore the extent of genetic influence, there is strong evidence that genetic predisposition is often a factor in dependency. Researchers have had difficulty assessing differences, however, between social causes of dependency learned in family settings and genetic factors related to heredity.

• The cultural model recognizes that the influence of culture is a strong determinant of whether or not individuals fall prey to certain addictions. For example, alcoholism is rare among Saudi Arabians, where obtaining alcohol is difficult and using alcohol is prohibited. In North America, on the other hand, the incidence of gambling addictions soared in the last two decades of the 20th century, mirroring the growth of the gaming industry. Half of all patients diagnosed as alcoholic are born into families where alcohol is used heavily, suggesting that familiar influence, genetic factors, or more likely both, play a role in the development of addiction.

• The blended model attempts to consider elements of all other models in developing a therapeutic approach to dependency. It holds that the mechanism of dependency is different for different individuals, and that each case must be considered on its own merits.

Physiological basis

Although the term addiction is sometimes often used loosely rather than as a medical classification, there are some physiological conditions related to everyday behaviors that are also related to the more commonly recognized mechanisms associated with addiction. Pleasurable activities cause the release of endorphins, and this endorphin-rush can conceivably become 'addictive'. Evolutionary biologists have suggested this process of attentuating pleasure pathways is part of the brain's natural system for ensuring that humans develop abiding interests. Since human societies depend on enduring attachments, many theorists suggest such addictions are not necessarily a problem. Other views, such as the those summarized in Buddhist concept of tanha, suggest trivial attachments are at the root of much human suffering.

The pathways oriented to endorphins, sometimes called pleasure centers originated in small organisms such as insects, which rely on the neurological system to help them find familiar sources of food.

Endorphins stimulate activity of the neurotransmitter dopamine after initially activating opioid receptors earlier in the nervous circuit. Increased dopamine activity is often met by a decrease in the number of receptors sensitive to dopamine. This process is called downregulation. The decreased number of receptors tends to result in reduced electrical activity along post-synaptic nerve pathways, unless some behavior or substance causes a continued high level of dopaminergic stimulation. The absence of a pleasurable sensation in conditions that were formally sufficient can cause a mild feeling of let-down after receptors have been downregulated. The increased requirement for dopamine to maintain the same electrical activity is the basis of both physiological tolerance and withdrawal associated with addiction.

The middle striatal reward pathway has been most strongly linked with addictive and reward behavior. This pathway utilizes dopamine as a neurotransmitter and receives presynaptic input (from earlier in the circuit--it gets signals from these earlier in the circuit cells) from cells that respond to cannibinoids, nicotine (receptor subtype is nicotinic), and from cells that respond to endogenous opioid substances such as endorphins or enkephalins. Cells that are said to respond to a particular neurotransmitter (or agonists) contain, at the postsynaptic end (receiving area of the cell) receptors for that neurotransmitter.

In cases of physical dependency on depressants of the central nervous system such as opioids, barbiturates, or alcohol, the absence of the substance sometimes leads to symptoms of severe physical discomfort and withdrawal can even result in death from alcohol and barbiturates (but is generally only very uncomfortable in the case of opioids despite media disinformation to the contrary). In these cases, a body has become so dependent on a chemical that it has stopped producing the necessary neurotransmitters required to maintain a comfortable status.

Opioids present extreme risks of dependency because they are chemically similar to endorphins, causing an upregulation of dopaminergic receptors without stimulation of the endorphin systems. Cocaine and amphetamines also pose risks associated with physical attenuation, in both cases because they cause increasees in the levels of the neurotransmitters dopamine and norepinephrine which acts indirectly to stimulate dopaminergic pathways in the brain.