Obsessive compulsive disorder (OCD) is a severely disabling anxiety disorder that affects approximately 2% of the Dutch population. Despite the availability of effective treatments, a relatively large percentage of OCD patients do not benefit from these therapies. On top of that, little is known about the long-term course of OCD.

In spite of the apparent similarities in the symptoms, individuals can exhibit a totally different focus when it comes to their obsessions and compulsions. Some individuals have a fear of germs and dirt and show a tendency to continuously clean themselves and their environment. Whereas others are afraid of impending disaster brought on by their own doing. For example, by (not) touching a particular colour or counting to a specific number. It is possible that these different types of obsessions and compulsions have a different course and do not react the same to treatment.

In order to answer these questions, seven mental health care organisations with expertise in OCD and scientific research decided to collaborate and started a cohort study. This study started in 2004 and in the following years persons with OCD were included and followed up. The aim of the study is to provide insight in the characteristics that make individuals with OCD prone to a chronic course. In addition, we expect that the findings from this study can help us tailor treatment to individuals with long lasting OCD symptoms.

Every participant provided information on numerous topics that might affect the onset and course of OCD. The data was gathered through personal interviews, self-report questionnaires, and a number of biological measurements, such as blood pressure, length, and weight. In addition, blood samples were collected during the first and fourth measurement. The interviews were repeated 2, 4, and 6 years after the start of the study.

During the study, participants provide data that will be used to answer the research questions. This data will be handled confidentially. This means that the information with regard to your mental health will be stored in a different database than the one that stores your contact details. A unique code is assigned to every NOCDA participant. All information regarding your mental health will be directly linked to this code, but not to your name. The research assistants who collect the data are the only ones that know your personal code. When reporting on the results of the study, researchers are not allowed to use your contact details and are only allowed to use this code.