In Europe, the rate of problem gambling is typically 0.5 to 3 percent. The "British Gambling Prevalence Survey 2007", conducted by the United Kingdom Gambling Commission, found approximately 0.6 percent of the adult population had problem gambling issues—the same percentage as in 1999. The highest prevalence of problem gambling was found among those who participated in spread betting (14.7%), fixed odds betting terminals (11.2%) and betting exchanges (9.8%). In Norway, a December 2007 study showed the amount of present problem gamblers was 0.7 percent.

Kimberly Young indicates that previous research links internet/computer addiction with existing mental health issues, most notably depression. She states that computer addiction has significant effects socially such as low self-esteem, psychologically and occupationally which led many subjects to academic failure.

According to a Korean study on internet/computer addiction, pathological use of the internet results in negative life impacts such as job loss, marriage breakdown, financial debt, and academic failure. 70% of internet users in Korea are reported to play online games, 18% of which are diagnosed as game addicts which relates to internet/computer addiction. The authors of the article conducted a study using Kimberly Young's questionnaire. The study showed that the majority of those who met the requirements of internet/computer addiction suffered from interpersonal difficulties and stress and that those addicted to online games specifically responded that they hoped to avoid reality.

The rate of people who have problems of shopping addiction is a very controversial matter, because the dividing line between pathological behaviours and those behaviours which, even if excessive, are socially accepted, is very difficult to determine. However, shopping addiction and other manifestations of the lack of self-control on spending are widespread problems which are constantly expanding. Studies using samples of the general population show that between 8% and 16% of the people have problems with excessive or uncontrolled purchases. Clinical studies give much lower figures, however, between 2% and 5%. According to the European Report on the programme for the prevention and treatment of personal problems related to consumer addiction, personal purchasing habits and over-indebtedness, 3% of European adults and 8% of European young people have a level of shopping addiction which could be considered as pathologic, that is, which seriously affects the life of the people who suffer from this. Other estimates for the prevalence of compulsive buying range from a low of 2 percent to 12 percent or more (in the U.S. population.

Most of people who have these problems neither receive nor ask for treatment. Those that ask for help only do it after years of suffering, when the addiction has caused very serious economic repercussion and has harmed the relationship with their family and social environment. For this reason and due to the lack of social consciousness about this problem, the unrecorded figure of people who suffer from these problems is very high. In addition to the severe cases of shopping addiction, an important part of consumers (between 30% and 50% of the population) have deficiencies with spending self-control or excessive purchases. According to the European Report, 33% of European adults and 46% of the European young people have minor or moderate problems with shopping addiction or lack of economic self-control.

Most research has focused on adult population or on college students, but little is known about epidemiology of behavioral addictions in adolescence. A study conducted by Villella "et al" looked at a group of students and the prevalence of various addictions. His results showed exercise addiction was the second most prevalent, after compulsive buying.

High risk groups that appear to be addicted to exercise include athletes in sports encouraging thinness or appearance standards, young and middle-age women, and young men.

In the United States, the percentage of pathological gamblers was 0.6 percent, and the percentage of problem gamblers was 2.3 percent in 2008. Studies commissioned by the National Gambling Impact Study Commission Act has shown the prevalence rate ranges from 0.1 percent to 0.6 percent. Nevada has the highest percentage of pathological gambling; a 2002 report estimated 2.2 to 3.6 percent of Nevada residents over the age of 18 could be called problem gamblers. Also, 2.7 to 4.3 percent could be called probable pathological gamblers.

According to a 1997 meta-analysis by Harvard Medical School's division on addictions, 1.1 percent of the adult population of the United States and Canada could be called pathological gamblers. A 1996 study estimated 1.2 to 1.9 percent of adults in Canada were pathological. In Ontario, a 2006 report showed 2.6 percent of residents experienced "moderate gambling problems" and 0.8 percent had "severe gambling problems". In Quebec, an estimated 0.8 percent of the adult population were pathological gamblers in 2002. Although most who gamble do so without harm, approximately 6 million American adults are addicted to gambling.

Signs of a gambling problem include:

- Using income or savings to gamble while letting bills go unpaid

- Repeated, unsuccessful attempts to stop gambling

- Chasing losses

- Losing sleep over thoughts of gambling

- Arguing with friends or family about gambling behavior

- Feeling depressed or suicidal because of gambling losses

As demonstrated by the chart below, numerous studies have examined factors which mediate substance abuse or dependence. In these examples, the predictor variables lead to the mediator which in turn leads to the outcome, which is always substance abuse or dependence. For example, research has found that being raised in a single-parent home can lead to increased exposure to stress and that increased exposure to stress, not being raised in a single-parent home, leads to substance abuse or dependence. The following are some, but by no means all, of the possible mediators of substance abuse.

As demonstrated by the chart below, numerous studies have examined factors which moderate substance abuse or dependence. In these examples, the moderator variable impacts the level to which the strength of the relationship varies between a given predictor variable and the outcome of substance abuse or dependence. For example, there is a significant relationship between psychobehavioral risk factors, such as tolerance of deviance, rebelliousness, achievement, perceived drug risk, familism, family church attendance and other factors, and substance abuse and dependence. That relationship is moderated by familism which means that the strength of the relationship is increased or decreased based on the level of familism present in a given individual.

Examples of mediators and moderators can be found in several empirical studies. For example, Pilgrim et al.’s hypothesized mediation model posited that school success and time spent with friends mediated the relationship between parental involvement and risk-taking behavior with substance use (2006). More specifically, the relationship between parental involvement and risk-taking behavior is explained via the interaction with third variables, school success and time spent with friends. In this example, increased parental involvement led to increased school success and decreased time with friends, both of which were associated with decreased drug use. Another example of mediation involved risk-taking behaviors. As risk-taking behaviors increased, school success decreased and time with friends increased, both of which were associated with increased drug use.

A second example of a mediating variable is depression. In a study by Lo and Cheng (2007), depression was found to mediate the relationship between childhood maltreatment and subsequent substance abuse in adulthood. In other words, childhood physical abuse is associated with increased depression, which in turn, in associated with increased drug and alcohol use in young adulthood. More specifically, depression helps to explain how childhood abuse is related to subsequent substance abuse in young adulthood.

A third example of a mediating variable is an increase of externalizing symptoms. King and Chassin (2008) conducted research examining the relationship between stressful life events and drug dependence in young adulthood. Their findings identified problematic externalizing behavior on subsequent substance dependency. In other words, stressful life events are associated with externalizing symptoms, such as aggression or hostility, which can lead to peer alienation or acceptance by socially deviant peers, which could lead to increased drug use. The relationship between stressful life events and subsequent drug dependence however exists via the presence of the mediation effects of externalizing behaviors.

An example of a moderating variable is level of cognitive distortion. An individual with high levels of cognitive distortion might react adversely to potentially innocuous events, and may have increased difficulty reacting to them in an adaptive manner (Shoal & Giancola, 2005). In their study, Shoal and Giancola investigated the moderating effects of cognitive distortion on adolescent substance use. Individuals with low levels of cognitive distortion may be more apt to choose more adaptive methods of coping with social problems, thereby potentially reducing the risk of drug use. Individuals with high levels of cognitive distortions, because of their increased misperceptions and misattributions, are at increased risk for social difficulties. Individuals may be more likely to react aggressively or inappropriately, potentially alienating themselves from their peers, thereby putting them at greater risk for delinquent behaviors, including substance use and abuse. In this study, social problems are a significant risk factor for drug use when moderated by high levels of cognitive distortions.

Over the past decade, the concept of Internet addiction has grown in terms of acceptance as a legitimate clinical disorder often requiring treatment. Researchers are divided over whether Internet addiction is a disorder on its own or a symptom of another underlying disorder. There is also debate over whether it should be classified as an impulse-control disorder or an obsessive-compulsive disorder rather than an addiction.

While the existence of Internet addiction is debated, self-proclaimed sufferers are resorting to the courts for redress. In one American case ("Pacenza v. IBM Corp."), the plaintiff argued he was illegally dismissed from his employment in violation of the Americans with Disabilities Act because of Internet addiction triggered by Vietnam War-related post-traumatic stress disorder (PTSD). The case was dismissed by the United States District Court for the Southern District of New York and affirmed on appeal to the United States Court of Appeals, Second Circuit in 2010 (case summarized in Glaser & Carroll, 2007).

About 25% of users fulfill Internet addiction criteria within the first six months of using the Internet. Many individuals initially report feeling intimidated by the computer but gradually feel a sense of "competency and exhilaration from mastering the technology and learning to navigate the applications quickly by visual stimulation" (Beard 374). The feeling of exhilaration can be explained by the way IAD sufferers often describe themselves as: bold, outgoing, open-minded, intellectually prideful, and assertive.

According to a study by Kathy Scherer, a psychologist from the University of Texas at Austin, "13% of college internet users fit the criteria for Internet addicts" (Scherer 1997). In her study, Scherer enlisted the help of 531 college students. She discovered that "72% of the Internet addicted students were men" (Scherer 1997).

The China Communist Youth League claimed in 2007 that over 17% of Chinese citizens between 13 and 17 were addicted to the Internet.

Public concern, interest in, and the study of, Internet over use can be attributed to the fact that it has become increasingly difficult to distinguish between the online and offline worlds. The Internet has tremendous potential to affect the emotions of humans and in turn, alter our self-perception and anxiety levels.

According to Maressa Orzack, director of the Computer Addiction Study at Harvard University's McLean Hospital, between 5% and 10% of Web surfers suffer some form of Web dependency.

According to the Center for Internet Addiction Recovery (whose director is Kimberly S. Young, a researcher who has lobbied for the recognition of net abuse as a distinct clinical disorder), "Internet addicts suffer from emotional problems such as depression and anxiety-related disorders and often use the fantasy world of the Internet to psychologically escape unpleasant feelings or stressful situations." More than half are also addicted to alcohol, drugs, tobacco, or sex.

Mark Griffiths states that "[t]he way of determining whether nonchemical (i.e., behavioral) addictions are addictive in a nonmetaphorical sense is to compare them against clinical criteria for other established drug-ingested addictions", and although his data is dated, and may no longer represent average Internet use accurately, Griffiths comes to the conclusion that the Internet does meet that criteria for addiction in a small number of users.

Scientists have found that compulsive Internet use can produce morphological changes in the structure of the brain. A study which analyzed Chinese college students who had been classified as computer addicts by the study designers and who used a computer around 10 hours a day, 6 days a week, found reductions in the sizes of the dorsolateral prefrontal cortex, rostral anterior cingulate cortex, supplementary motor area and parts of the cerebellum compared to students deemed "not addicted" by the designers. It has been theorized that these changes reflect learning-type cognitive optimizations for using computers more efficiently, but also impaired short-term memory and decision-making abilities—including ones in which may contribute to the desire to stay online instead of be in the real world.

Patricia Wallace PhD, Senior Director, Information Technology and CTY Online, at the Johns Hopkins University Center for Talented Youth argues that based on the case histories that have surfaced, no one denies that excessive involvement with certain psychological spaces on the net can have serious effects on a person's life. She explains that, at a large university in New York, the dropout rate among freshmen newcomers rose dramatically as their investment in computers and Internet access increased, and the administrators learned that 43% of the dropouts were staying up all night on the Internet.

Research carried out on people undergoing treatment, as well as on the general population has revealed a negative correlation between age and addiction. As the age of people increases there is a lower number of shopping addicts. This data was confirmed by the 1999 European Report.

It must be noted that the age of diagnosis is much later than the age when the problems of addiction begin. Most addicts have the first symptoms of addiction in their twenties, but do not ask for help nor accept treatment until more than ten years afterwards. To explain the higher incidence of shopping addiction in young people, it has been shown that younger people have been born, and have grown up, in an increasingly consumerist society and they have endured the impact of publicity and marketing from birth. On the contrary, it is very unusual to find shopping addiction problems in people older than 65 years.

Some scholars believe that codependency is not a negative trait, and does not need to be treated, as it is more likely a healthy personality trait taken to excess. Codependency in nonclinical populations has some links with favourable characteristics of family functioning.

Stan Katz states that codependence is over-diagnosed, and that many people who could be helped with shorter-term treatments instead become dependent on long-term self-help programs. The language of, symptoms of, and treatment for codependence derive from the medical model suggesting a disease process underlies the behavior. However, there is no evidence that codependence is caused by a disease process.

In their book, “Attached.”, Dr. Amir Levine and Rachel S. F. Heller, address what they call the “codependency myth” by asserting that attachment theory is a more scientific and helpful model for understanding and dealing with attachment in adults.

Excessive computer use may result in, or occur with:

- Lack of face to face social interaction

- Computer vision syndrome

Overuse is often defined as a "dependence syndrome," which is the term used by the World Health Organization (WHO Expert Committee, 1964) to replace "addiction" or "habituation." This is categorised either as substance abuse, such as from psychoactive drugs, alcohol and tobacco under ICD-10, or a behavioral addiction, such as a mobile phone addiction.

Substance use disorders can be defined by 11 factors, according to the DSM-5, including: (1) use in larger quantities or for longer than initially intended, (2) a desire to cut down or control use, (3) spending a great deal of time obtaining, using, or recovering from the substance, (4) craving, (8) use in situations in which it is physically hazardous, (9) continued use of the substance despite adverse physical or psychological consequences associated with use, and (11) withdrawal symptoms.

Smartphone addiction can be compared to substance use disorders in that smartphones provide the drug (entertainment and connection) while acting as the means by which the drug is consumed. A study conducted at Alabama State University on the effects of smartphones on students, defines the issue by stating that we are not addicted to smartphones themselves, but that we "are addicted to the information, entertainment, and personal connections [that a smartphone] delivers." People have an affinity for constant entertainment, and smartphones provide the quickest, most easily accessible route to it.

A conceptual model of PIU has been developed based on primary data collected from addiction researchers, psychologists, and health providers as well as older adolescents themselves. That study identified seven concepts, or clusters, that make up PIU using a concept mapping approach. These seven clusters are: psychosocial risk factors; physical impairment; emotional impairment; social and functional impairment; risky Internet use; impulsive Internet use; and Internet use dependence. The last three constructs have not been previously identified. Risky Internet use are behaviors that increase risks of adverse consequences. It is not just the amount of time spent on the Internet that puts an adolescent at risk; how the time is spent is also an important consideration. The impulsive use construct describes an inability to maintain balance or control of internet use in relation to everyday life. Finally, the dependent use construct reflects the more severe symptoms that are typically associated with addictions, such as withdrawal symptoms. Thus, internet addiction may represent a severe form of PIU.

Other research also stresses the fact that the Internet addiction disorder is not a unidimensional but a multidimensional construct. Various facets of Internet use must be differentiated because of their differential predictors, mechanisms and consequences. Online activities which, if done in person, would normally be considered troublesome, such as compulsive gambling, or shopping, are sometimes called "net compulsions".

Prevalence of mobile phone overuse depends largely on definition and thus the scales used to quantify a subject's behaviors. Two scales are in use, the 20-item self-reported Problematic Use of Mobile Phones (PUMP) scale, and the Mobile Phone Problem Use Scale (MPPUS), which have been used both with adult and adolescent populations. There are variations in the age, gender and percentage of the population affected problematically according to the scales and definitions used. The prevalence among British adolescents aged 11–14 was 10%. In India, addiction is stated at 39-44% for this age group. Under different diagnostic criteria, the estimated prevalence ranges from 0 to 38%, with self-attribution of mobile phone addiction exceeding the prevalence estimated in the studies themselves. The prevalence of the related problem of Internet addiction was 4.9-10.7% in Korea, and is now regarded as a serious public health issue.

Behaviors associated with mobile-phone addiction differ between genders. Women are more likely to develop addictive mobile phone behavior than men. Men experience less social stress than women and use their mobile phones less for social purposes. Older people are less likely to develop addictive mobile phone behavior because of different social usage, stress and greater self-regulation.

Individuals with exercise addiction may put exercise above family and friends, work, injuries, and other social activities. If not identified and treated, an exercise addiction may lead to a significant decline in one's health.

The consequences of oniomania, which may persist long after a spree, can be devastating, with marriages, long-term relationships, and jobs all feeling the strain. Further problems can include ruined credit history, theft or defalcation of money, defaulted loans, general financial trouble and in some cases bankruptcy or extreme debt, as well as anxiety and a sense of life spiraling out of control. The resulting stress can lead to physical health problems and ruined relationships, or even suicide.

Another growing area is social media addiction. Psychology researchers surveyed 253 undergraduate students at the University of Albany and found that not only is social media (particularly Facebook) itself potentially addictive, those who use it may also be at greater risk for substance abuse.

Exercise provides benefits for our bodies, but to some people, the benefits turn into health hazards. To some exercisers, rigorous physical activity becomes the central aspect of their lives. When a preoccupation with exercise has become routine, a person is considered addicted to exercise or exercise dependent. A study done shows why people may become addicted to exercise, especially running. One of the reasons people become addicted to exercise is because of the release of mood-enhancing chemicals known as endorphins. Endorphins increase the sensation of pleasure, which is why people feel good about themselves after they exercise. Endorphins are also responsible for the "runner's high." Recent studies have lent weight to the alternative theory that the addictive appeal of exercise is due to the production of endocannabinoids, naturally produced chemicals that bind to the brain's CB1 receptor, rather than to endorphin production. Those who suffer from exercise addiction will go through physical and emotional withdrawals in the absence of exercise, just like a person who is addicted to other substances, such as drugs or alcohol. Although in many cases, running is a better alternative than substance abuse. The findings in this study conclude that there is a link between negative addiction to running and interpersonal difficulties, which is common in other addictive behaviors as well.

Another form of behavior that is still being investigated is obsessive sun tanning as a behavioral addiction. In a recent study, researchers have proved that many frequent tanners demonstrate signs and symptoms adapted from substance abuse or dependence criteria. Many people who admit to being frequent tanners say they tan to look good, feel good, and to relax. People who partake in excessive tanning are usually completely aware of the health risks associated with it, just like addicted smokers are completely aware of the health risks of smoking. The health hazards are even more severe for high-risk age groups such as teenagers and young adults. Due to the fact that the health risks do not deter tanners from their habit, they are exhibiting self-destructive behavior that resembles the characteristics of those who suffer from substance abuse.

Frequent tanners have said a primary reason why they participate in artificial tanning is to experience the "feel good" feeling tanning salons have to offer. Researchers have found that ultraviolet (UV) radiation from tanning beds offers mood-enhancing effects that act as a treatment for seasonal affective disorder (SAD). SAD is when a person exhibits minor depression during seasonal changes, such as during the winter months. Ultraviolet radiation has been proven to increase the level of melatonin in the body. Melatonin plays a key role in sleep patterns and is suggested to reduce anxiety levels. Thus, those who go tanning experience a sense of relaxation afterwards. This sensation is what possibly drives tanners to continue tanning regardless of the health risks. More research needs to be done, but many researchers are beginning to add tanning to the list of addictive processes.

Street children in many developing countries are a high risk group for substance misuse, in particular solvent abuse. Drawing on research in Kenya, Cottrell-Boyce argues that "drug use amongst street children is primarily functional – dulling the senses against the hardships of life on the street – but can also provide a link to the support structure of the ‘street family’ peer group as a potent symbol of shared experience."

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. According to DARA Thailand, the index assesses potential problems in seven categories: medical, employment/support, alcohol, other drug use, legal, family/social, and psychiatric.

In order to maintain high-quality performance, some musicians take chemical substances. Some musicians take drugs or alcohol to deal with the stress of performing. As a group they have a higher rate of substance abuse. The most common chemical substance which is abused by pop musicians is cocaine, because of its neurological effects. Stimulants like cocaine increase alertness and cause feelings of euphoria, and can therefore make the performer feel as though they in some ways ‘own the stage’. One way in which substance abuse is harmful for a performer (musicians especially) is if the substance being abused is aspirated. The lungs are an important organ used by singers, and addiction to cigarettes may seriously harm the quality of their performance. Smoking causes harm to alveoli, which are responsible for absorbing oxygen.

The dependence potential of a drug varies from substance to substance, and from individual to individual. Dose, frequency, pharmacokinetics of a particular substance, route of administration, and time are critical factors for developing a drug dependence.

An article in "The Lancet" compared the harm and dependence liability of 20 drugs, using a scale from zero to three for physical dependence, psychological dependence, and pleasure to create a mean score for dependence. Selected results can be seen in the chart below.

A number of groups have been identified as being at greater risk of developing cannabis dependence and include adolescent populations, Aboriginal and Torres Strait Islanders (in Australia) and people suffering from mental health conditions.

Psychological dependence is a form of dependence that involves emotional–motivational withdrawal symptoms (e.g., a state of unease or dissatisfaction, a reduced capacity to experience pleasure, or anxiety) upon cessation of drug use or engagement in certain behaviors. Physical and psychological dependence are sometimes classified as a facet or component of addiction, such as in the DSM-IV-TR; however, some drugs which produce dependence syndromes do not produce addiction, and vice versa, in humans. Addiction and psychological dependence are both mediated through reinforcement, a form of operant conditioning, but are associated with different forms of reinforcement. Addiction is a compulsion for rewarding stimuli that is mediated through positive reinforcement. Psychological dependence, which is mediated through negative reinforcement, involves a desire to use a drug or perform a behavior to avoid the unpleasant withdrawal syndrome that results from cessation of exposure to it.

Psychological dependence develops through consistent and frequent exposure to a stimulus. Behaviors which can produce observable psychological withdrawal symptoms (i.e., cause psychological dependence) include physical exercise, shopping, sex and self-stimulation using pornography, and eating food with high sugar or fat content, among others. Behavioral therapy is typically employed to help individuals overcome psychological dependence upon drugs or maladaptive behaviors that produce psychological dependence.

Withdrawal is the body's reaction to abstaining from a substance upon which a person has developed a dependence syndrome. When dependence has developed, cessation of substance use produces an unpleasant state, which promotes continued drug use through negative reinforcement; i.e., the drug is used to escape or avoid re-entering the associated withdrawal state. The withdrawal state may include physical-somatic symptoms (physical dependence), emotional-motivational symptoms (psychological dependence), or both. Chemical and hormonal imbalances may arise if the substance is not introduced. Psychological stress may also result if the substance is not re-introduced.

Infants also suffer from substance withdrawal, known as Neonnatal Abstinence Syndrome (NAS) which has severe and life-threatening effects on growing fetus. Addiction to drugs and alcohol in expecting mothers does not only cause NAS but also an array of other issues which can continually affect the infant throughout his/her lifetime. The type of drug which was abused during the months of pregnancy has many different effects on the child which can affect the infant in many ways throughout his/her life.