Obsessive-Compulsive Disorder (OCD)

Obsessive-Compulsive Disorder (OCD) is a mental disorder consisting of two parts: obsessions (intrusive, unwanted, and repetitive thoughts, urges, or images that don’t go away and are generally unwanted, or ego-dystonic) and/or compulsions (repetitive physical behaviours or mental acts performed, meant to reduce the anxiety caused by the obsessions). Typical themes include contamination or cleaning, checking, symmetry, ordering or counting, as well as fears of harm to self or others. Obsessions can also be violent, sexual, or religious in nature.


There is a lifetime prevalence of 2% and it is highly disabling. OCD symptoms (not diagnoses) are on a variant of normal. Symptoms occurs in over 25% of adults, and developmentally appropriate rituals and superstitions are common in children. The actual diagnosis of OCD requires the presence of obsessions or compulsions that are time-consuming (> 1 hour/day total) or cause major distress/impairment in functioning for the individual.

Risk Factors

OCD is strongly heritable (half of all cases have a family history) and has a strong neurobiologic basis. Environmental factors also play a role. Males typically present at an earlier age compared to females, but 60% of diagnoses are female.[1] Patients have varying degrees of insight into the irrationality of their OCD symptoms, and some have no insight. Poor prognostic factors include: early onset, poor insight, schizotypal features, and thought/action compulsions.

Course of illness

The course of OCD is typically chronic and fluctuating, although studies involving youth suggest that over half experience remission by early adulthood. The mean age of onset of OCD is bimodal, with peaks at 11 years and 23 years. Early-onset OCD is more common among males, is more likely comorbid with tics and more severe. Without treatment, remission rates in adults are low (20% for those reevaluated 40 years later).[2]

Comorbid conditions

About 60-90% of patients with OCD also have a comorbid disorder, including mood, anxiety, somatoform disorders, substance use disorders, psychotic disorders, and bipolar disorders. The lifetime prevalence for MDD in persons with OCD is 67% and for social phobia about 25%. The incidence of Tourette's in patients with OCD is 5-7%, and between 20-30% of patients with OCD have a history of tics.[3]

Criterion A

Presence of obsessions, compulsions, or both:

Obsessions are defined by (1) and (2):

  1. Recurrent and persistent thoughts, urges, or images that are experienced, at some time during the disturbance, as intrusive and unwanted, and that in most individuals cause marked anxiety or distress.
  2. The individual attempts to ignore or suppress such thoughts, urges, or images, or to neutralize them with some other thought or action (i.e., by performing a compulsion).
Note: Young children may not be able to articulate the aims of these behaviours or mental acts.

Compulsions are defined by (1) and (2):

  1. Repetitive behaviors (e.g., hand washing, ordering, checking) or mental acts (e.g., praying, counting, repeating words silently) that the individual feels driven to perform in response to an obsession or according to rules that must be applied rigidly.
  2. The behaviors or mental acts are aimed at preventing or reducing anxiety or distress, or preventing some dreaded event or situation; however, these behaviors or mental acts are not connected in a realistic way with what they are designed to neutralize or prevent, or are clearly excessive.
Criterion B

The obsessions or compulsions are time-consuming (e.g., take more than 1 hour per day) or cause clinically significant distress or impairment in social, occupational, or other important areas of functioning.

Criterion C

The obsessive-compulsive symptoms are not attributable to the physiological effects of a substance (e.g., a drug of abuse, a medication) or another medical condition.


The mnemonic “Having OCD is MURDER” can be used to remember the criteria for obssessive-compulsive disorder.[4]

  • M Mind – patient aware symptoms arise in the mind
  • U Unpleasant thoughts
  • R Resist – patient must want and try to resist obsessive thoughts
  • D Displeasure of feeling the obsession
  • E Ego-dystonic
  • R Repetitive thoughts
Criterion D

The disturbance is not better explained by the symptoms of another mental disorder:



Specify if:

  • With good or fair insight: The individual recognizes that obsessive-compulsive disorder beliefs are definitely or probably not true or that they may or may not be true.
  • With poor insight: The individual thinks obsessive-compulsive disorder beliefs are probably true.
  • With absent insight/delusional beliefs: The individual is completely convinced that obsessive-compulsive disorder beliefs are true.

Specify if:

  • Tic-related: The individual has a current or past history of a tic disorder.
OCD History and Screening

High sensitivity screening questions and a good OCD history includes the following:

  1. Do you experience unwanted thoughts, images or impulses that repeatedly enter your mind, despite trying to get rid of them? For example, worries about dirt or germs, or thoughts of bad things happening? (Screening for obsessions)
  2. Do you ever feel driven to repeat certain acts over and over? For example, repeatedly washing your hands, cleaning, checking doors or work over and over, rearranging things to get it just right, or having to repeat thoughts in your mind to feel better? (Screening for compulsions)
  3. Does this waste significant time or cause problems in your life? For example, interfering with school, work or seeing friends?(Does the individual potentially meet DSM-5 criteria?)

Psychometric Scales for Obsessive-Compulsive Disorder

Yale–Brown Obsessive Compulsive Scale (Y-BOCS)
Rater Clinician
Description A 10-item clinician-administered scale. It is the most widely used rating scale for OCD. Remission is considered to be a 25% reduction in Y-BOCS score.
DownloadY-BOCS Download
Name Rater Description Download
Yale–Brown Obsessive Compulsive Scale (Y-BOCS) Clinician A 10-item clinician-administered scale. It is the most widely used rating scale for OCD. Remission is considered to be a 25% reduction in Y-BOCS score. Y-BOCS Download

The pathophysiology of OCD is still being investigated, and there are multiple theories. Some research has been shown that streptococcal throat infections are related to elevated risks of mental disorders, particularly OCD and tic disorders.[5] Functional neuroimaging from PET, fMRI, and SPECT have shown that several brain structures are implicated in OCD. The caudate nucleus (located in the basal ganglia) shows increased levels of activity, and activity levels normalizes after successful treatment of OCD, either with medications or cognitive behaviour therapy.[6] The orbitofrontal cortex and striatal dysfunction is also implicated.[7]

Medication-induced OCD symptoms

There is some emerging evidence that second-generation antipsychotics, in particular clozapine and olanzapine, can lead to the development of OCD symptoms (not diagnosis).[8][9]

The differential diagnosis for OCD includes anxiety disorders, depression, complex tics, eating disorders, and psychosis. OCD is considered to be on a spectrum that encompasses comorbid conditions like hoarding disorder, excoriation disorder, trichotillomania disorder and body dysmorphic disorder. All these conditions are generally characte rized by specific types of preoccupations and/or repetitive behaviours. It is important that the clinician be aware of all of these related conditions, as they must be differentiated from one another. See Criterion D of the DSM-5 diagnostic criterion for a full differential diagnosis consideration.

Is it anxiety, psychosis, or OCD?

One of the key features of OCD is that the obsessions/compulsions are egodystonic, meaning the individual does not want these thoughts (it's distressing!). In generalized anxiety, the worries are usually egosyntonic, meaning the individual feels the worries are beneficial to some degree. Similarly, psychosis (specifically delusions) can be confused with OCD. Again, individuals with OCD usually have insight that their symptoms are causing an impairment. Individuals with delusions/psychosis usually lack insight. However, in clinical practice, it can sometimes be difficult to distinguish between the three.[10] This is where clinical experience and good history taking comes in!

Is it somatic delusions/illness anxiety disorder or OCD?

Individuals with somatic delusions or illness anxiety disorder are convinced that that they have an illness (e.g. - AIDS), despite testing results or medical reassurance. On the contrary, individuals with OCD are preoccupied that they could be infected or are performing excessive rituals to prevent this.

Various treatment guidelines exist for the treatment of OCD, including NICE (2005), APA (2007) guidelines. The following treatment recommendations are based on the 2014 Canadian Clinical Practice Guidelines for anxiety , posttraumatic stress and obsessive-compulsive disorders:[11]


A specialized form of CBT, called Exposure and Response/Ritual Prevention Therapy (ERP) is the gold standard and first-line treatment for OCD, and favoured over medications. In ERP, patients are exposed to situations that trigger obsessions, and are taught strategies to prevent the compulsive response that would temporarily relieve their anxiety. Patients gradually become desensitized to the feared stimulus, resulting in improved OCD symptoms. To do ERP successfully, patients must have significant buy-in into the therapy, as it can be a very distressing experience. Long-term maintenance of improvement has been shown in both children and adults. Involving family members to reduce family accommodation of the compulsions is also important.[12]


If ERP does not improve OCD symptoms sufficiently or is not feasible (i.e - patient cannot face their symptoms directly), treatment with an SSRI should be considered. Treating with medications alone confer only a marginal improvement in symptoms! It is important to set up a patient's expectations of how much improvement they will have on medications (patients can expect a maximum of a 30-35% reduction a medication). Remember too that relapse is also more likely with discontinuation of SSRI therapy than with CBT/ERP. Patients must also be treated longer (at least 3 months) with doses near the maximum recommended doses (resulting in increased rates of adverse effects).[13] Intravenous clomipramine has also been shown to be as effective, and if not more effective than SSRIs.[14] It is important to monitor for serotonin syndrome if the patient is on both an SSRI and clomipramine. Well-designed studies have shown that there is no difference between ERP alone versus ERP plus pharmacotherapy. There is overall a low placebo response rate to medications (compare this to major depressive disorder, where the placebo response can be at least 35%).[15]

Pharmacotherapy for OCD

1st line Escitalopram, fluoxetine, fluvoxamine, paroxetine, sertraline
2nd line Citalopram, clomipramine, mirtazapine, venlafaxine XR
3rd line IV citalopram, IV clomipramine, duloxetine, phenelzine, tramadol, tranylcypromine
Adjunctive therapy First-line: aripiprazole, risperidone
Second-line: memantine, quetiapine, topiramate
Third-line: amisulpride, celecoxib, citalopram, granisetron, haloperidol, IV ketamine, mirtazapine, N-acetylcysteine, olanzapine, ondansetron, pindolol, pregabalin, riluzole, ziprasidone
Not recommended: buspirone, clonazepam, lithium, morphine
Not recommended Clonazepam, clonidine, desipramine
  • IV = intravenous; XR = extended release.

2. American Psychiatric Association: Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition. Arlington, VA, American Psychiatric Association, 2013.
3. American Psychiatric Association: Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition. Arlington, VA, American Psychiatric Association, 2013.