Functions of compulsions in obsessive-compulsive disorder.

Objectives: The key function of compulsions in obsessive-compulsive disorder (OCD) is to alleviate anxiety or distress caused by the obsessions, but compulsions may also have other functions. The main aim of this study was to systematically ascertain what motivates individuals with OCD to perform compulsions.

Method: A total of 108 adults with OCD were assessed with the Yale-Brown Obsessive Compulsive Scale (Y-BOCS) and the Functions of Compulsions Interview. The latter instrument elicits the functions of identified compulsions.

Results: The functions of 218 compulsions were identified. The mean number of functions per compulsion in the whole sample was 2.94 and the vast majority of compulsions (85.3%) were performed for more than one reason. The total number of functions of compulsions endorsed for the three main compulsions correlated with Y-BOCS total scores (r = 0.37, p < 0.001). Compulsions were most frequently performed automatically and to decrease distress or anxiety, but there was substantial variation, depending on the type of compulsion. Hoarding was often performed for reasons not related to any other compulsion (involving a perceived need for collected objects), whereas ordering/symmetry/repeating compulsions were frequently performed to achieve a 'just right' feeling. Checking was frequently performed because of the belief that something bad or unpleasant would happen if one failed to check; washing/cleaning compulsions were most frequently performed to decrease distress or anxiety and automatically, and mental compulsions were performed automatically far more often than for other reasons.

Conclusions: The majority of compulsions have more than one function and they are often performed automatically. The finding of different functions of compulsions in different types of compulsions provides some support to the subtyping of OCD on the basis of obsessions and compulsions. Identifying functions of compulsions allows better understanding of the functional relationship between obsessions and compulsions, which may have implications for cognitive-behavioural therapy of OCD.