Specific genes predispose people to drug addiction—it's one of the behavioral disorders most strongly corrolated with genetic makeup—but environmental factors, especially trauma and mistreatment in childhood, also correlate strongly with addiction. . Examples such as physical or sexual abuse, and unpredictable expectations and behavior of parents, increase a person's risk for developing addiction.

Sensation-seeking has been studied as having a strong relationship with addictive personalities.

Individual differences in women's estrogen cycles may be related to the expression of BPD symptoms in female patients. A 2003 study found that women's BPD symptoms were predicted by changes in estrogen levels throughout their menstrual cycles, an effect that remained significant when the results were controlled for a general increase in negative affect.

There is a strong correlation between child abuse, especially child sexual abuse, and development of BPD. Many individuals with BPD report a history of abuse and neglect as young children, but causation is still debated. Patients with BPD have been found to be significantly more likely to report having been verbally, emotionally, physically, or sexually abused by caregivers of either gender. They also report a high incidence of incest and loss of caregivers in early childhood. Individuals with BPD were also likely to report having caregivers of both sexes deny the validity of their thoughts and feelings. Caregivers were also reported to have failed to provide needed protection and to have neglected their child's physical care. Parents of both sexes were typically reported to have withdrawn from the child emotionally and to have treated the child inconsistently. Additionally, women with BPD who reported a previous history of neglect by a female caregiver and abuse by a male caregiver were significantly more likely to experience sexual abuse by a non-caregiver.

It has been suggested that children who experience chronic early maltreatment and attachment difficulties may go on to develop borderline personality disorder. Writing in the psychoanalytic tradition, Otto Kernberg argues that a child's failure to achieve the developmental task of and failure to overcome splitting might increase the risk of developing a borderline personality. A child's inability to tolerate delayed gratification at age four does not predict later development of BPD.

Elements of the family and social environment may also play a role in the development and maintenance of conduct disorder. For instance, antisocial behavior suggestive of conduct disorder is associated with single parent status, parental divorce, large family size, and young age of mothers. However, these factors are difficult to tease apart from other demographic variables that are known to be linked with conduct disorder, including poverty and low socioeconomic status. Family functioning and parent-child interactions also play a substantial role in childhood aggression and conduct disorder, with low levels of parental involvement, inadequate supervision, and unpredictable discipline practices reinforcing youth's defiant behaviors.

Peer influences have also been related to the development of antisocial behavior in youth, particularly peer rejection in childhood and association with deviant peers. Peer rejection is not only a marker of a number of externalizing disorders, but also a contributing factor for the continuity of the disorders over time. Hinshaw and Lee (2003) also explain that association with deviant peers has been thought to influence the development of conduct disorder in two ways: 1) a “selection” process whereby youth with aggressive characteristics choose deviant friends, and 2) a “facilitation” process whereby deviant peer networks bolster patterns of antisocial behavior. In a separate study by Bonin and colleagues, parenting programs were shown to positively affect child behavior and reduce costs to the public sector.

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.

The development of conduct disorder is not immutable or predetermined. A number of interactive risk and protective factors exist that can influence and change outcomes, and in most cases conduct disorder develops due to an interaction and gradual accumulation of risk factors. In addition to the risk factors identified under cause, several other variables place youth at increased risk for developing the disorder, including child physical abuse and prenatal alcohol abuse and maternal smoking during pregnancy. Protective factors have also been identified, and most notably include high IQ, being female, positive social orientations, good coping skills, and supportive family and community relationships.

However, a mere correlation between a particular risk factor and a later developmental outcome (such as conduct disorder) cannot be taken as definitive evidence for a causal link. Co-variation between two variables can arise, for instance, if they represent age-specific expressions of similar underlying genetic factors. For example, the tendency to smoke during pregnancy (SDP) is subject to substantial genetic influence (D'Onofrio et al., 2007), as is conduct disorder. Thus, the genes that dispose the mother to SDP may also dispose the child to CD following mitotic transmission. Indeed, Rice et al. (2009) found that in mother-fetus pairs that were not genetically related (by virtue of in-vitro fertilisation), no link between SDP and later conduct problems arose. Thus, the distinction between causality and correlation is an important consideration.

Not only are there significant health risks associated with compulsive hoarding, but scientists are also trying to pinpoint how significant the interference is with occupational and social functioning in a hoarder's daily life. In a pool of compulsive hoarders, 42% found their behavior problematic to the 63% of their family and friends who saw the behavior as problematic. The findings suggest that individuals who hoard may exhibit impaired sensitivity to their own and others’ emotions, and conversely, relate the world around them by forming attachments to possessions rather than to people. Lower emotional intelligence among hoarding patients may also impact their ability to discard and organize their possessions. With such detrimental characteristics, comprehensive research has been performed to find a cure. Although this is ongoing research, most investigations have found that only a third of patients who hoard show an adequate response to these medications and therapeutic interventions.

With the modifications to the DSM, insurance coverage for treatments will change as well as special education programs.

Some evidence based on brain lesion case studies also suggests that the anterior ventromedial prefrontal and cingulate cortices may be involved in abnormal hoarding behaviors, but sufferers of such injuries display less purposeful behavior than other individuals who hoard compulsively, thus making the involvement of these brain structures unclear. Other neuropsychological factors that have been found to be associated with individuals exhibiting hoarding behaviors include slower and more variable reaction times, increased impulsivity, and decreased spatial attention. A study comparing neural activity in hoarders, people with OCD, and a control group when deciding to throw possessions away found that when hoarders were trying to decide to throw away their own possessions, they had lower activity in the anterior cingulate cortex and insula regions of the brain. The study suggested this lower activity was related to "problems in identifying the emotional significance of a stimulus, generating appropriate emotional response, or regulating affective state during decision making." Hoarders had normal levels of activity in those regions when making decisions about possessions that did not belong to them.

Another theory suggests a possible relationship between histrionic personality disorder and antisocial personality disorder. Research has found 2/3 of patients diagnosed with histrionic personality disorder also meet criteria similar to those of the antisocial personality disorder, which suggests both disorders based towards sex-type expressions may have the same underlying cause. Women are hypersexualized in the media consistently, ingraining thoughts that the only way women are to get attention is by exploiting themselves, and when seductiveness isn't enough, theatricals are the next step in achieving attention. Men can just as well be flirtatious towards multiple women yet feel no empathy or sense of compassion towards them. They may also become the center of attention by exhibiting the "Don Juan" macho figure as a role-play.

Some family history studies have found that histrionic personality disorder, as well as borderline and antisocial personality disorders, tend to run in families, but it is unclear if this is due to genetic or environmental factors. Both examples suggest that predisposition could be a factor as to why certain people are diagnosed with histrionic personality disorder, however little is known about whether or not the disorder is influenced by any biological compound or is genetically inheritable. Little research has been conducted to determine the biological sources, if any, of this disorder.

Kleptomania is frequently thought of as being a part of obsessive-compulsive disorder (OCD), since the irresistible and uncontrollable actions are similar to the frequently excessive, unnecessary, and unwanted rituals of OCD. Some individuals with kleptomania demonstrate hoarding symptoms that resemble those with OCD.

Prevalence rates between the two disorders do not demonstrate a strong relationship. Studies examining the comorbidity of OCD in subjects with kleptomania have inconsistent results, with some showing a relatively high co-occurrence (45%-60%) while others demonstrate low rates (0%-6.5%). Similarly, when rates of kleptomania have been examined in subjects with OCD, a relatively low co-occurrence was found (2.2%-5.9%).

Negative parenting practices and parent–child conflict may lead to antisocial behavior, but they may also be a reaction to the oppositional and aggressive behaviors of children. Factors such as a family history of mental illnesses and/or substance abuse as well as a dysfunctional family and inconsistent discipline by a parent or guardian can lead to the development of behavior disorders.

Insecure parent–child attachments can also contribute to ODD. Often little internalization of parent and societal standards exists in children with conduct problems. These weak bonds with their parents may lead children to associate with delinquency and substance abuse.

Family instability and stress can also contribute to the development of ODD. Although the association between family factors and conduct problems is well established, the nature of this association and the possible causal role of family factors continues to be debated.

Low socioeconomic status is associated with poor parenting, specifically with inconsistent discipline and poor parental monitoring, which are then associated with an early onset of aggression and antisocial behaviors.

Externalizing problems are reported to be more frequent among minority-status youth, a finding that is likely related to economic hardship, limited employment opportunities, and living in high-risk urban neighborhoods.

Kleptomania or klopemania is the inability to refrain from the urge for stealing items and is usually done for reasons other than personal use or financial gain. First described in 1816, kleptomania is classified in psychiatry as an impulse control disorder. Some of the main characteristics of the disorder suggest that kleptomania could be an obsessive-compulsive spectrum disorder.

The disorder is frequently under-diagnosed and is regularly associated with other psychiatric disorders, particularly anxiety and eating disorders, and alcohol and substance abuse. Patients with kleptomania are typically treated with therapies in other areas due to the comorbid grievances rather than issues directly related to kleptomania.

Over the last 100 years, a shift from psychotherapeutic to psychopharmacological interventions for kleptomania has occurred. Pharmacological treatments using selective serotonin reuptake inhibitors (SSRIs), mood stabilizers and opioid receptor antagonists, and other antidepressants along with cognitive behavioral therapy, have yielded positive results.

Compulsive decluttering is a pattern of behavior that is characterized by an excessive desire to discard objects in one's home and living areas. Other terms for such behavior includes obsessive compulsive spartanism. The homes of compulsive declutterers are often empty. It is the antonym of compulsive hoarding.

According to Professor Emily Simonoff of the Institute of Psychiatry, Psychology and Neuroscience, "childhood hyperactivity and conduct disorder showed equally strong prediction of antisocial personality disorder (ASPD) and criminality in early and mid-adult life. Lower IQ and reading problems were most prominent in their relationships with childhood and adolescent antisocial behaviour."

Impulsive behavior, and especially impulsive violence predisposition has been correlated to a low brain serotonin turnover rate, indicated by a low concentration of 5-hydroxyindoleacetic acid (5-HIAA) in the cerebrospinal fluid (CSF). This substrate appears to act on the suprachiasmatic nucleus in the hypothalamus, which is the target for serotonergic output from the dorsal and median raphe nuclei playing a role in maintaining the circadian rhythm and regulation of blood sugar. A tendency towards low 5-HIAA may be hereditary. A putative hereditary component to low CSF 5-HIAA and concordantly possibly to impulsive violence has been proposed. Other traits that correlate with IED are low vagal tone and increased insulin secretion. A suggested explanation for IED is a polymorphism of the gene for tryptophan hydroxylase, which produces a serotonin precursor; this genotype is found more commonly in individuals with impulsive behavior.

IED may also be associated with lesions in the prefrontal cortex, with damage to these areas, including the amygdala, increasing the incidence of impulsive and aggressive behavior and the inability to predict the outcomes of an individual's own actions. Lesions in these areas are also associated with improper blood sugar control, leading to decreased brain function in these areas, which are associated with planning and decision making. A national sample in the United States estimated that 16 million Americans may fit the criteria for IED.

Codependency is a type of dysfunctional helping relationship where one person supports or enables another person's drug addiction, alcoholism, gambling addiction, poor mental health, immaturity, irresponsibility, or under-achievement. Among the core characteristics of codependency, the most common theme is an excessive reliance on other people for approval and a sense of identity.

Given its grassroots origin, the precise definition of codependency varies based on the source but can be generally characterized as a subclinical and situational or episodic behavior similar to that of dependent personality disorder. In its broadest definition, a codependent is someone who cannot function from their innate self and whose thinking and behavior is instead organized around another person, or even a process, or substance. In this context, people who are addicted to a substance, like drugs, or a process, like gambling or sex, can also be considered codependent. In its most narrow definition, it requires one person to be physically or psychologically addicted, such as to heroin, and the second person to be psychologically dependent on that behavior. Some users of the codependency concept use the word as an alternative to using the concept of dysfunctional families, without statements that classify it as a disease.

Externalizing disorders are frequently comorbid or co-occurring with other disorders. Individuals who have the co-occurrence of more than one externalizing disorder have homotypic comorbidity, whereas individuals who have co-occurring externalizing and Internalizing disorders have heterotypic comorbidity. It is not uncommon for children with early externalizing problems to develop both internalizing and further externalizing problems across the lifespan.

Research into genetic associations in antisocial personality disorder is suggestive that ASPD has some or even a strong genetic basis. Prevalence of ASPD is higher in people related to someone afflicted by the disorder. Twin studies, which are designed to discern between genetic and environmental effects have reported significant genetic influences on antisocial behavior and conduct disorder.

In the specific genes that may be involved, one gene that has seen particular interest in its correlation with antisocial behavior is the gene that encodes for Monoamine oxidase A (MAO-A), an enzyme that breaks down monomamine neurotransmitters such as serotonin and norephinephrine. Various studies examining the gene's relationship to behavior have suggested that variants of the gene that results in less MAO-A being produced, such as the 2R and 3R alleles of the promoter region have associations with aggressive behavior in men. The association is also found influenced by negative experience in early life, with children possessing a low-activity variant (MAOA-L) with who experienced such maltreatment being more likely to develop antisocial behavior than those with the high-activity variants (MAOA-H). Even when environmental interactions (e.g. emotional abuse) are controlled for, a small association between MAOA-L and aggressive and antisocial behavior remains.

The gene that encodes for the serotonin transporter (SCL6A4), a gene that is heavily researched for its associations with other mental disorders, is another gene of interest in antisocial behavior and personality traits. Genetic associations studies have suggested that the short "S" allele is associated with impulsive antisocial behavior and ASPD in the inmate population. However, research into psychopathy find that the long "L" allele is associated with the Factor 1 traits of psychopathy, which describes its core affective (e.g. lack of empathy, fearlessness) and interpersonal (e.g. grandiosity, manipulativeness) personality disturbances. This is suggestive of two different forms, one associated more with impulsive behavior and emotional dysregulation, and the other with predatory aggression and affective disturbance, of the disorder.

Various other gene candidates for ASPD have been identified by a genome-wide association study published in 2016. Several of these gene candidates are shared with attention-deficit hyperactivity disorder, with which ASPD is comorbid.

Compulsive behavior is defined as performing an act persistently and repetitively without it necessarily leading to an actual reward or pleasure. Compulsive behaviors could be an attempt to make obsessions go away. The act is usually a small, restricted and repetitive behavior, yet not disturbing in a pathological way. Compulsive behaviors are a need to reduce apprehension caused by internal feelings a person wants to abstain from or control. A major cause of the compulsive behaviors is said to be obsessive–compulsive disorder (OCD). "The main idea of compulsive behavior is that the likely excessive activity is not connected to the purpose to which it appears directed." Furthermore, there are many different types of compulsive behaviors including, shopping, hoarding, eating, gambling, trichotillomania and picking skin, checking, counting, washing, sex, and more. Also, there are cultural examples of compulsive behavior.

An addictive behavior is a behavior, or a stimulus related to a behavior (e.g., sex or food), that is both rewarding and reinforcing, and is associated with the development of an addiction. Addictions involving addictive behaviors are normally referred to as behavioral addictions.

Psychoanalytic theories incriminate authoritarian or distant attitudes by one (mainly the mother) or both parents, along with conditional love based on expectations the child can never fully meet. Using psychoanalysis, Freud believed that lustfulness was a projection of the patient's lack of ability to love unconditionally and develop cognitively to maturity, and that such patients were overall emotionally shallow.

He believed the reason for being unable to love could have resulted from a traumatic experience, such as the death of a close relative during childhood or divorce of one's parents, which gave the wrong impression of committed relationships. Exposure to one or multiple traumatic occurrences of a close friend or family member's leaving (via abandonment or mortality) would make the person unable to form true and affectionate attachments towards other people.

Two epidemiological studies of community samples approximated the lifetime prevalence of IED to be 4–6%, depending on the criteria set used. A Ukrainian study found comparable rates of lifetime IED (4.2%), suggesting that a lifetime prevalence of IED of 4–6% is not limited to American samples. One-month and one-year point prevalences of IED in these studies were reported as 2.0% and 2.7%, respectively. Extrapolating to the national level, 16.2 million Americans would have IED during their lifetimes and as many as 10.5 million in any year and 6 million in any month.

Among a "clinical" population, a 2005 study found the lifetime prevalence of IED to be 6.3%.

Prevalence appears to be higher in men than in women.

Of US subjects with IED, 67.8% had engaged in direct interpersonal aggression, 20.9% in threatened interpersonal aggression, and 11.4% in aggression against objects. Subjects reported engaging in 27.8 high-severity aggressive acts during their worst year, with 2–3 outbursts requiring medical attention. Across the lifespan, the mean value of property damage due to aggressive outbursts was $1603.

A study in the March 2016 "Journal of Clinical Psychiatry" suggests a relationship between infection with the parasite "Toxoplasma gondii" and psychiatric aggression such as IED.

ADHD often precedes the onset of ODD, and approximately half of children with ADHD, Combined Type also have ODD. ODD is a risk factor for CD and frequently precedes the onset of CD symptoms. Children with an early onset of CD symptoms, with at least one symptom before age 10 years, are at risk for more severe and persistent antisocial behavior continuing into adulthood. Youth with early-onset conduct problems are particularly at risk for ASPD (note that an onset of CD prior to age 15 is part of the diagnostic criteria for ASPD), whereas CD is typically limited to adolescence when youth's CD symptoms begin during adolescence.

Genetically informed studies of the personality characteristics typical of individuals with psychopathy have found moderate genetic (as well as non-genetic) influences. On the PPI, fearless dominance and impulsive antisociality were similarly influenced by genetic factors and uncorrelated with each other. Genetic factors may generally influence the development of psychopathy while environmental factors affect the specific expression of the traits that predominate. A study on a large group of children found more than 60% heritability for "callous-unemotional traits" and that conduct problems among children with these traits had a higher heritability than among children without these traits.