The medical or biomedical theory of abnormality views the causes of abnormal psychology to be biological as well as the symptoms and cures. Examples of this might include hormone imbalances or differences in brain structure. Unconscious conflict would be classified under the psychanalytic psychology, attachment theory under social or developmental psychology, conditioning under behavioral psychology, and thought patterns under cognitive psychology.

Each branch of psychology has many explanations for psychopathology, including failure of self-realization (humanistic), unconscious conflict (psychodynamic), cognitive biases (cognitive), and biochemical imbalances (psychobiological). Although some people may believe that fate plays a role in whether someone develops a disorder, fate is not a scientific phenomenon that any branch of psychology includes in the study of psychopathology.

Psychodynamic theorists are very firm in their belief about the interactions between the id and ego during the early, formative years of a person's life. They propose that there is a battle between anxiety-provoking id impulses and anxiety-reducing defense mechanisms.

Cognitive theorists believe that the mind and patterns of thinking are largely in control of how a person views and responds to life's events. Cognitive theorists believe that people with unipolar depression persistently view events and situations in life in negative ways. As a result of these defeatist perceptions, such people sink into feelings of gloom, helplessness, and depression.

Developmental psychopathology is the study of the development of psychological disorders, including autism, ADHD, and schizophrenia. This subfield of psychopathology focuses on a life course perspective in examining the trajectory of psychological disorders.

Biological theorists believe that generalized anxiety disorder is caused chiefly by biological factors. One associated belief is that, due to low activity of the neurotransmitter gamma-aminobutyric acid (GABA), excessive worrying and anxiety manifests in a person. Biological treatments for generalized anxiety disorder include antianxiety drug therapy, relaxation training, and biofeedback.

Any traumatic event can trigger post-traumatic stress disorder. Some of the most likely to do so include combat, disasters, abuse of any kind, victimization, and torture.

The major paradigm for dissociative disorders is the diathesis-stress model. This model depends on the idea that psychological disorders occur when a person is predisposed to the disorder and experiences significant stress. Research has indicted that many dissociative patients experienced childhood physical or sexual abuse, which were the cause of significant stress. According to this model, these patients also had a predisposition, or diathesis, to dissociate easily. This means they are easily hypnotized and prone to engage in fantasy. Dissociation was a method of avoidance for these patients. In other words, dissociating from reality allowed them to escape their stressful experiences, protect themselves from emotional trauma, and block out unpleasant memories.

There are higher rates of mood and anxiety disorders in women for a combination of reasons, including hormonal differences, higher rates of sexual assault, less societal power and control, and more willingness to get help (which increases the rates, though not the occurances). The average woman is less aggressive than the average man, but that does not relate to anxiety/mood disorders and in fact brings down the rates of other types of disorders, such as antisocial personality disorder.

The diathesis-stress model states that disorders are caused by both a predisposition to the disorder and a life stress that serves as a trigger. The only example that follows that pattern is Thomas's family history (diathesis) and stressful life events (trauma).