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OCD severity in people seen by the AIS


People sometimes wonder how severe patients being seen by a specialist service are. The following is a description of the severity of symptoms that individuals seen by the AIS present with, based on a relatively large sample of patients seen over the last 14 years.


The data come from 81 patients seen between 2006 and 2020. Three quarters (74%) were seen in the last ten years.

The majority of people were male (63%).

The mean ± SD age was 41.5 ± 12.7 years. The youngest person was 16 years, and the oldest person was 73 years.

All patients had a primary diagnosis of obsessive-compulsive disorder. Many had secondary diagnoses. The most common was Moderate Depressive Disorder (33%), and the second most common was Anankastic Personality Disorder (15%). Other common disorders included Social Phobia (6%) and Hypochondriacal disorder (6%).

Y-BOCS score

The distribution of Y-BOCS score (clinician-rated) is shown below as a box and whisker plot. The centre line is the median, and the two bars above this represent the higher and lower 25% of cases. This means that 50% of cases fall within the range of the box.

Y-BOCS scores of assessments
Y-BOCS scores of assessments


In terms of severity classification, this was as follows: mild (4%); moderate (8%); severe (50%); and extreme (38%). This means that around 9 out of 10 patients seen had an OCD severity of at least severe.


It can be seen from the above data that the majority of people referred to the AIS have OCD that is severe or extreme. This is associated with high levels of incapacity and impaired functioning in almost all areas (e.g. work, family, social).

The majority of the evidence base for OCD - particularly in terms of psychological therapy - involves people with lower levels of severity. If we assume that the average Y-BOCS score for psychological therapies is around 25, this would mean that only 17% of our patients would fall below this range.

One implication is that the majority of people seen by the AIS are not only likely to benefit from medication, but many will need it to get maximum benefit from psychological therapy. Another implication is that many patients are likely to struggle to get maximum benefit from the therapies available in mainstream mental health services. This is because:

a) people will need regular therapy, usually delivered in their home (or where the symptoms are most problematic), and for durations greater than one hour;

b) augmentation of antidepressants is likely to be required. The confidence to manage this in secondary care is not always available, and regular review is necessary to manage possible adverse effects. Such regular review (perhaps every 2-4 weeks) is often difficult to deliver.

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Date of publication