The Biological Approach to OCD

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  • Assumes that psychological disorders are physical illnesses with physical causes- they have major psychological symptoms 

Genetic factors:

Billet Et al

  • meta anaylsis of twin studies 
  • identical twins- if one had OCD then 68% of the time both twins had it 
  • non-identical twins- if one had OCD then 31% of the time both twins had it

Pauls et al 

  • 10% of people with immediate relatives with OCD also suffered from it 
  • only 2% of the general population have OCD 

However, No study has found a 100% concordance rate, so genetics cannot be the full factor for OCD. 

Children may imitate Obessive and Compulsive behaviour from relative. 

Concordance rates also do not prove OCD is caused by genetics. General anxiety might be genetic which may develop into OCD.

Biochemical factors


  • SSRIs (increase serotonin levels) can reduce symptoms of OCD in 50-60% of cases. 

Zohar et al 

  • Also found SSRIs lifted symptoms in 60% of patients with OCD 

This is not 100% in all cases, so there must be more to understanding OCD. 

The serotonin link is correlational, so it does not show cause and effect, it may be that decreased serotonin levels are a symptom of OCD rather…


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