Based on the personality traits associated with being codependent and narcissistic, it is not rare for such people to be involved in romantic relationships. The venn diagram below shows traits that may be complementary to one another:

Relationships between codependent and narcissist people

1. Self-concept is developed based on how their parents treat them.
2. Work hard to please others to receive positive feedback from others and often have low self-esteem.
3. Healthy modes of self-expression and self-directedness are insufficiently developed.
4. Efface or downplay one's importance, needs, opinions, voices, and desires in favor of prioritizing others and adopting an other-oriented perspective.
5. Feel overly responsible for other people (e.g., goals, needs, demands, requirements) and take the blame for interpersonal problems.
6. Distrust or feel speculative of one's views and subjective world.
7. Unwilling to assert oneself for fear of being perceived as egotistical.
8. Typically experience recurring feelings of insecurity and tend to be unaware/doubt the validity of their feelings, experience, and needs since they fear receiving negative judgment (e.g., being considered as selfish) and frequently receive undesirable feedback (e.g., verbal aggression, neglect, isolation, rejection, disparagement, disapproval, blame, criticism, punishment) when being assertive or demonstrating genuine aspects of their personality. 
9. Deem that two components of narcissism and co-narcissism need to co-exist in interpersonal interactions. They often adjust their orientation (i.e., narcissism vs. co-narcissism) across different situations based on the role taken by the person they interact with.  

Characteristics of Co-Narcissism

Co-narcissism refers to the unique sets of characteristics exhibited by the offspring of narcissistic parents. Co-narcissism arises as a natural consequence of growing up in an environment dominated by narcissistic parents or as coping with the challenging dynamics of such an environment. 

New York University

Narcissism is a personality trait characterized by an inflated self-concept of one’s own worth, a strong sense of entitlement, and a tendency to act selfishly. Narcissism is a spectrum with those at the highest end classified as having narcissistic personality disorder (NPD).

Narcissism

Rappoport, A. (2005). Co-narcissism: How we accommodate to narcissistic parents. The Therapist, 1, 1-8.

Co-narcissism: How we accommodate to narcissistic parents (Rappoport, 2005)

The one factor model of narcissism puts essentially the whole spectrum of narcissism onto one level. The term "narcissism" is often used as an umbrella term for both minor and extreme (NPD) forms where there's no distinction between different levels of expression.

One Factor Model of Narcissism

In the last twenty years, psychologists have transitioned to a more hierarchical study of narcissism composed of at least two distinct dimensions: grandiose narcissism and vulnerable narcissism. This model provided much needed clarity between the definitions, operations, assessments, and outcomes of narcissism.

Two Factor Model of Narcissism

In recent years, three factor models of narcissism have emerged, which have further clarified its core components. This model is composed of antagonism, agentic extraversion, and narcissistic neuroticism. Individuals with NPD have high scores in all three factors. 

The three factor model demonstrates both what's shared across the dimensions of narcissism and what's unique to grandiose and vulnerable narcissism. It also shows the distinct relationship between narcissism and self esteem, which has been a gray area in the past. 

Three Factor Model of Narcissism

Narcissism isn’t synonymous with high self-esteem; this association depends on which components of narcissism are emphasized.

- High self-esteem
- Grandiose narcissism

Narcissism ≠ High Self Esteem

- Current conceptualization of narcissism's underlying motives
- Narcissistic status pursuit model

Underlying Motives of Narcissism

Not much is known about the social outcomes of vulnerable narcissism. However, there's a dual-pathway approach to the social consequences of grandiose narcissism.

- Admiration pathway
- Rivalry pathway

Social Outcomes of Narcissism

Co-Narcissism

Many factors contribute to the development of NPD in a person. The following outline some of the potential factors:
- One can be genetically predisposed to NPD;
- Negative events experienced during developmental stages such as being rejected and having low self esteem can lead to NPD in adulthood; 
- Excessive praise as a child.

Potential causes of Narcissistic Personality Disorder

NPD can often occur with other mental health conditions making it challenging to determine which disorder is causing symptoms. Such comorbidities include:
- Substance use disorders;
- Additional personality disorders including antisocial PD, borderline PD, histrionic PD, and schizotypal PD.

Comorbidities in people with NPD

Even though more research is needed to determine if NPD is responsible for neurological differences, one study in Germany indicates it does. Abnormalities found in this study include:
- Differences in grey matter in the prefrontal, insular, right prefrontal, and anterior cingulate areas of the brain;
- Differences in white matter in the frontal lobe.

Differences seen in the brains of people with NPD

Many different methods can be used to diagnose patients with NPD and to rule out other potential diagnoses. The method used will depend on the setting the patient is seen in.

Methods used to diagnose patients with NPD.

Pharmacological treatment for NPD has not been established yet but medicine can be used to treat symptoms. For example, antidepressants, antipsychotics, and mood stabilizers can be prescribed. Additionally, long-term therapy can be used to work on symptoms and develop coping skills. Types of psychotherapy for people with NPD may include psychodynamic, transference-focused, and schema-focused therapy.

Treatment options for people with NPD.

Complications that arise in people with NPD will generally be due to symptoms caused by comorbid conditions. For instance, when NPD is present with substance use disorder hostility is more common. It is also important to note that death by suicide is also common in people with NPD.

Long-term impacts of NPD

The story of neurosurgeon Christopher Duntsch is a good representation of how narcissism can present itself and be harmful to others. There is a documentary called "Dr. Death: The Undoctored Story" that explains this story. Additionally, his story was also told in a TV-Show called "Dr. Death".

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