We read with interest the article on obsessive—compulsive disorder (OCD) and delusions, by O'Dwyer & Mark (2000). The suggestion of a continuum of pathological beliefs in OCD from ‘none’ to ‘delusional intensity’ suggests the possibility of another continuum of mental disorders from OCD to psychosis.

The authors presented five cases of OCD associated with delusional beliefs. They concluded that these patients are best considered within an OCD management plan. Moreover, they do not recommend use of long-term antipsychotic medication since they consider that such patients are unlikely to respond. However, none of the five patients they reported upon was treated with low doses of an atypical antipsychotic in order to augment the action of serotonin-specific antidepressants, the preferred pharmacotherapy in OCD.

Recently, we have successfully treated a man in his 50s who presented with a 7-year history of typical OCD. His problem was suitable for treatment using exposure and ritual prevention, combined with an antidepressant. He was referred for behavioural psychotherapy at the specialist unit based at the Maudsley Hospital. Although motivated to try this treatment he later found it too difficult to continue with this approach. He therefore remained under the care of his general practitioner (GP) who treated him with fluoxetine 20 mg daily, on which he had only a very slight improvement in his symptoms. When we saw him at the request of his GP he was asking for relief from anxiety symptoms. Small doses of thioridazine produced unacceptable side-effects, so olanzapine 2.5 mg was substituted. After approximately 4 weeks his symptoms were almost completely gone, and at a follow-up appointment he stated that for the first time after 7 years of rituals and obsessions, he felt 90% better.

Initially, our choice of olanzapine was determined by the patient's need for anxiolysis. However, there is emerging evidence that olanzapine may augment the action of fluoxetine in the treatment of individuals with OCD (Reference Weiss, Potenza and McDougleWeiss et al, 1999). Another possibility is that olanzapine was having a direct action on psychotic phenomena. Whatever the case, we would suggest that contrary to the recommendations for management offered by O'Dwyer & Marks (Reference O'Dwyer and Marks2000) some treatment-resistant cases of OCD might respond to a therapeutic trial with low doses of an atypical antipsychotic in addition to a serotonin-specific antidepressant as usually recommended.