Compulsive and repetitive use of alcohol or drug or other substances may result in tolerance to the effect of the drug and withdrawal symptoms when use is reduced or stopped. This, along with substance abuse is considered Substance Use Disorders.

Substance dependence can be diagnosed with physiological dependence, evidence of tolerance or withdrawal, or without physiological dependence.

Definition

Drug addiction is a pathological or abnormal condition which arises due to frequent drug use.

There is progression of acute drug use to the development of drug-seeking behavior causing decreased, slowed ability to respond to naturally rewarding stimuli.

The Diagnostic and Statistical Manual of Mental Disorders (DSM-IV) has categorized three stages of addiction:

1. Preoccupation/anticipation,
2. Binge/intoxication,
3. Withdrawal/negative affects.

There is (i) an overpowering desire or need (compulsion) to continue taking the drug and to obtain it by any means; (ii) a tendency to increase the dose; (iii) a psychic (psychological) and generally a physical dependence on the effects of the drug; and (iv) detrimental effects on the individual and on society.

Drug habituation (habit): repeated consumption of a drug characterized by(i) a desire (but not a compulsion) to continue taking the drug for the sense of improved well-being which it engenders; (ii) little or no tendency to increase the dose; (iii) some degree of psychic dependence on the effect of the drug, but absence of physical dependence and hence of an abstinence syndrome [withdrawal], and (iv) detrimental effects, if any, primarily on the individual.

Addictionis a primary, chronic, neurobiologic disease, with genetic, psychosocial, and environmental factors influencing its development and manifestations. It is characterized by behaviors that include one or more of the following: impaired control over drug use, compulsive use, continued use despite harm, and craving.

A definition of addiction proposed by professor Nils Bejerot:
"An emotional fixation (sentiment) acquired through learning, which intermittently or continually expresses itself in purposeful, stereotyped behavior with the character and force of a natural drive, aiming at a specific pleasure or the avoidance of a specific discomfort.”

Causes

• Stimulants (psychic addiction, moderate to severe; withdrawal is purely psychological and psychosomatic):

o Amphetamine and methamphetamine
o Cocaine
o Nicotine

• Sedatives and hypnotics (psychic addiction, mild to severe, and physiological addiction, severe; abrupt withdrawal may be fatal):

o Alcohol
o Barbiturates
o Benzodiazepines, particularly flunitrazepam, triazolam, temazepam, and nimetazepam
o Methaqualone and the related quinazolinone sedative-hypnotics

• Opiate and opioid analgesics (psychic addiction, mild to severe, physiological addiction, mild to moderately severe; abrupt withdrawal is unlikely to be fatal):

o Morphine and codeine, the two naturally occurring opiate analgesics
o Semi-synthetic opiates, such as heroin (diacetylmorphine), oxycodone, buprenorphine, and hydromorphone
o Fully synthetic opioids, such as fentanyl, meperidine/pethidine, and methadone

The following are some of the symptoms of Drug addiction :

• life circumstances change
• social Milestones are met or missed
• New social roles are created while old ones are abandoned.
• Adolescence or young adulthood
• But surprisingly a significant amount of cocaine users may not initiate use until middle adulthood.
• However, some people enter these roles earlier or later than their same age peers.

Pathophysiology

Acute effects
Release and prolonged action of dopamine and serotonin within the reward circuit.

Reward circuit

Mesolimbic system, is characterized by the interaction of several areas of the brain.

• The ventral tegmental area (VTA) :dopaminergic neurons - respond to glutamate. - increase the dopamine release in the mesolimbic pathway
• The nucleus accumbens (NAc) :GABA neurons.- conditioned behaviors and involved in the increased sensitivity to drugs as addiction progresses.
• The prefrontal cortex, more specifically the anterior cingulate and orbitofrontal cortices - a behavior -motivation originates
• Hippocampus - learning and memory - alters dopamine levels

Role of dopamine

Nearly all addictive drugs target the brain’s reward system by flooding the circuit with dopamine. As a result, the chemical’s impact on the reward circuit is lessened, reducing the abuser’s ability to enjoy the things that previously brought pleasure. This decrease compels those addicted to dopamine to increase the drug consumption in order to attempt to bring their "feel-good" hormone level back to normal —an effect known as tolerance. Unfortunately, this blocking can also cause relapses in depression, and can increase addictive behaviors.

Stress response

The corticotropin-releasing factor (CRF) activates the hypothalamic-pituitary-adrenal axis (HPA) and other stress systems in the extended amygdala. This activation influences the dysregulated emotional state associated with drug addiction.
Enkephalin as a product of HPA Effect is an endogenous opioid peptide that regulates pain.

Behavior

strong, drug seeking behaviors in which the addict persistently craves and seeks out drugs, despite the knowledge of harmful consequences.
Addictive drugs produce a reward, which is the euphoric feeling.
this behavior is most likely a result of the synaptic changes which have occurred due to repeated drug exposure.
The drug seeking behavior is induced by glutamatergic projections from the prefrontal cortex.

Allostasis
Addiction to drugs can cause damage to a brain and body as an organism enters the pathological state this altered stability of changed behaviour from normal physiological limits is also known as allostatic load.
Thus the ability to overcome the depressed state following drug use begins to decrease. This creates a constant state of depression. These people are always in the state of stress. Thus the presence of environmental stressors may induce heightened responses.

Neuroplasticity

Neuroplasticity is the acknowledged change in learning and memory. There is physical change in the synapse between two communicating neurons, characterized by increased gene expression, altered cell signaling, and the formation of new synapses between the communicating neurons. addictive drugs hijack this mechanism in the reward system so that motivation is geared towards procuring the drug rather than natural rewards.
Behavior gears towards seeking the drug,

Sensitization

Sensitization is the increase in sensitivity to a drug after prolonged use.

Individual mechanisms of effect The basic mechanisms by which different substances activate the reward system are as described above, but vary slightly among drug classes.

Depressants

Depressants such as alcohol, barbiturates, and benzodiazepines : increase the affinity of the GABA receptor : facilitate relaxation and pain relief.

Stimulants

Stimulants such as amphetamines, nicotine, and cocaine : increase dopamine signaling in the reward system or directly stimulating dopamine release, or by blocking : cause a pleasant feeling in the body and euphoria, known as a high. Once this high wears off, the user may feel depressed. This makes them want another dose of the drug, and can worsen the addiction.

Addiction is a complex but treatable condition.
For most people, addiction becomes chronic, with relapses possible even after long periods of abstinence.
addiction may require continued treatments to increase the intervals between relapses and diminish their intensity.
Through treatment tailored to individual needs, people with drug addiction can recover and lead fulfilling lives.
CBT (cognitive behavioral therapy ) sees addiction as a behavior rather than a disease and subsequently curable.

Anti-addictive drugs

As per the type of addictive substance taken by the patient the treatment plan is managed.

Behavioral programming

(1) Behavioral marital therapy
(2) Community reinforcement approach
(3) Cue exposure therapy
(4) Contingency management strategies.
Social skills training adjunctive to inpatient treatment of alcohol dependence is probably efficacious.