Co-Occurrence of Personality Disorder and Substance Use Disorders
The most commonly co-occurring DSM diagnoses are personality disorders and substance use disorders (which include alcohol and other drugs). A research study by Zimmerman and Coryell (1989) found that about 43-77% of people diagnosed with personality disorders would also meet the criteria for an alcohol use disorder at some point during their lives. Other researchers, such as Verheul and colleagues (1995, 1998), have looked at the co-occurrence between personality disorders and substance use disorders from the opposite angle and have reported that 44% of people with alcohol use disorders would meet criteria for a personality disorder, and 77% of people who abuse opiates would meet criteria for a personality disorder. These researchers identified that Cluster B personality disorders (most notably Borderline Personality Disorder and Antisocial Personality Disorder) were the most common personality disorders associated with substance use disorders.
There are several hypotheses that attempt to explain this high co-occurrence between personality disorders and substance use disorders. Some experts suspect the high co-occurrence is related to impulsivity, namely that people with poorer impulse control (such as people with Antisocial and Borderline Personality Disorder) also have a hard time resisting urges and cravings to use substances. In other words, the use of the mood-altering substances and the immediate "good feeling" that follows, is so appealing that people with poor impulse control find it difficult to resist. This is true despite the damaging consequences that follow repeated and continuous substance use. While this rewarding and reinforcing effect of drug use applies broadly to all people who use drugs, it is especially difficult for people with impulse control problems.
Another proposed explanation for the high co-occurrence between personality disorders and substance use disorders might be described as a "self-medication" hypothesis. This hypothesis suggests that some people tend to use mood-altering substances in order to cope with stress or with difficult emotions. This hypothesis is particularly applicable for people with Borderline Personality Disorder who tend to feel emotions with great intensity and who take a longer time to calm down than do people without this disorder. Many people with Borderline Personality Disorder use mood-altering substances in order to get immediate relief from emotionally intense situations; for instance, when feelings of anxiety or anger run very high. This "self-medication" hypothesis may also apply to people with Cluster C personality disorders, characterized by anxiety. For instance, someone with Avoidant Personality Disorder might plan to go to a party but become extremely anxious, anticipating rejection and even ridicule. Having an alcoholic beverage beforehand might serve to reduce his anxiety in the moment. However, over time, repeated use could leads to a substance use diagnosis.
A third hypothesis to explain the high co-occurrence of substance use disorders and personality disorders has to do with excitement-seeking behavior. Certain personality disorders are associated with a tendency to become easily bored. This tendency is characteristic of people with Narcissistic, Histrionic, or Antisocial Personality Disorders (Cluster B). Some experts believe that such people come to see drug use as exciting relief from frequent boredom. The exciting quality of illicit drug use stems from the intrinsic effects of different drugs (i.e., the "high" associated with them) and because they are typically used with other people in socially exciting and/or risky circumstances.
Co-Occurrence of Personality Disorder and Eating Disorders
Eating disorders, including Anorexia Nervosa and Bulimia Nervosa, are another group of disorders that commonly co-occur with personality disorders. As a group, eating disorders are defined by severe dietary restriction to such a degree that it endangers one's health. Dietary restriction is generally thought to be a method used by people with eating disorders to regulate intense emotions. The Borderline Personality Disorder is characterized by this lack of emotional regulation. For people with an eating disorder, the ability to severely restrict food intake may provide them with a sense of relief. At least they can control something (hunger) even when other things in their life seem beyond their control.
The impulsively associated with Borderline Personality Disorder is also thought to be a key to this disorder's affinity with eating disorders. This is particularly true of Bulimia Nervosa and Binge-Eating Disorder. These are disorders marked by impulsive binge episodes. The binge episode is followed by shame and remorse over the failure to retain control.
The relationship between the Obsessive Compulsive Personality Disorder and eating disorders seems to revolve around two primary symptoms that are associated with both disorders: characteristic rigidity and need for control. This is particularly noticeable in people with Anorexia Nervosa as they control their caloric intake in a highly rigid and even ritualized manner.
The Avoidant Personality Disorder is characterized by feelings of inadequacy and social anxiety. This sense of inadequacy may represent a deep concern over the acceptability of one's physical appearance. This excessive concern over physical appearances can resonate with people who have eating disorders. They attempt to control their weight and body shape in a misguided effort to become more socially acceptable. Unfortunately, it is almost always the case that no amount of weight loss or dietary restriction is ever enough to make that core feeling of inadequacy go away.
Co-Occurrence of Personality Disorders with other Personality Disorders
Research suggests that personality disorders frequently co-occur with each other. About half of all people who meet the criteria for one personality disorder will also meet the criteria for at least one other (Fowler, O'Donohue & Lilienfeld, 2007). There is a particularly high rate of co-occurrence between personality disorders within the same cluster (Skodol, 2005). For example, people with Borderline Personality Disorder, a Cluster B diagnosis, are also fairly likely to meet criteria for other Cluster B diagnoses, including Narcissistic, Histrionic, or Antisocial Personality disorders. Likewise, people who meet criteria for Schizotypal Personality Disorder (a Cluster A diagnosis) are fairly likely to also meet criteria for other Cluster A diagnoses, including Paranoid or Schizoid Personality Disorder. Since the clusters are thought to consist of personality disorders that have some features in common, this pattern of co-occurrence makes sense.