Schizoid personality disorder (, often abbreviated as SPD or SzPD) is a personality disorder characterized by a lack of interest in social relationships, a tendency towards a solitary or sheltered lifestyle, secretiveness, emotional coldness, detachment and apathy. Affected individuals may be unable to form intimate attachments to others and simultaneously possess a rich and elaborate but exclusively internal fantasy world. Other associated features include stilted speech, a lack of deriving enjoyment from most, if not all, activities, feeling as though one is an "observer" rather than a participant in life, an inability to tolerate emotional expectations of others, apparent indifference when praised or criticized, a degree of asexuality and idiosyncratic moral or political beliefs. Symptoms typically start in late childhood or adolescence.
The cause of SPD is uncertain, but there is some evidence of links and shared genetic risk between SPD, other cluster A personality disorders (such as schizotypal personality disorder) and schizophrenia. Thus, SPD is considered to be a "schizophrenia-like personality disorder". It is diagnosed by clinical observation, and it can be very difficult to distinguish SPD from other disorders such as Asperger syndrome, with which it is sometimes comorbid. This is complicated by clinical overlap in symptoms and the existence of a long-noted subgroup of mostly male Asperger's patients who go on to develop SPD.
The effectiveness of psychotherapeutic and pharmacological treatments for the disorder have yet to be empirically and systematically investigated. While low doses of atypical antipsychotics were originally also used to treat some symptoms of SPD, their use is no longer recommended. The substituted amphetamine bupropion may be used to treat associated anhedonia. However, it is not general practice to treat SPD with medications, other than for the short-term treatment of acute co-occurring disorders (e.g. depression). Talk therapies such as cognitive behavioral therapy (CBT) may not be effective, because people with SPD may have hard time forming a good working relationship with a therapist. People with SPD rarely seek treatment for their condition.
SPD is a poorly studied disorder, and there is little clinical data on SPD because it is rarely encountered in clinical settings. Studies have generally reported a prevalence of less than 1% (a few estimates, however, have been as high as 4%). It affects slightly more males than females. SPD is linked to negative outcomes, including a significantly compromised quality of life, reduced overall functioning even after 15 years and one of the lowest levels of "life success" of all personality disorders (measured as "status, wealth and successful relationships"). Bullying is particularly common towards schizoid individuals. Suicide may be a running mental theme for schizoid individuals, though they are not likely to actually attempt one. Some symptoms of SPD (e.g. solitary lifestyle and emotional detachment), however, have been stated as general risk factors for serious suicidal behaviour.