November 2019 By

Obsessive-Compulsive Disorder (OCD)

Obsessive-Compulsive Disorder (OCD) is a mental disorder that consists of (1) obsessions (intrusive, unwanted, and repetitive thoughts, urges, or images that don’t go away and are generally unwanted, or ego-dystonic) and/or (2) 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 (about 20% achieve remission after 40 years).[2] In pediatric populations, 41% remain symptomatic after 5 years.[3]


About 60-90% of patients with OCD also have a comorbid mental 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 is 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.[4]

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)

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
Note: Young children may not be able to articulate the aims of these behaviours or mental acts.
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.

Criterion D

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


The mnemonic “Having OCD is MURDER” can be used to remember the criteria for obssessive-compulsive disorder.[5]

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


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.

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

  1. Obsessions: Do you ever get intrusive or unwanted thoughts, images, or impulses that repeatedly enter your mind, despite you trying to get rid of them? For example, worries about dirt or germs, or thoughts of bad things happening?
  2. Compulsions: Do you ever feel driven to do certain things over and over again? 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?
  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, Criterion B?)


Obsessions can be external or internal:

  • External obsessions: contamination, objects, smells, asymmetry, mismatched items
  • Internal obsessions: ego-dystonic thoughts (violent, sexual, etc.), always ask: “are these thoughts intrusive in nature?”

Common Obsessions

Contamination Concerns about dirt, germs, body waste, illness
Symmetry Needing things “just so”, even, or lined up a certain arbitrary way
Aggressive Most commonly focused on inadvertent harm, such as being responsible for a fire or break-in; also includes horrific thoughts or images of deliberately harming others, such as stabbing a loved one or pushing a stranger in front of a car
Sexual Disturbing sexual thoughts that are not consistent with an individual’s orientation or cultural norms, such as someone with a same-sex preference having unpleasant hetero-erotic thoughts, or unwanted inappropriate sexual thoughts about children
Religious Examples include thoughts about selling one’s soul to the devil, deliberately thinking inappropriate thoughts about major religious figures, or committing mortal sins
Somatic Exaggerated fears of contracting a serious illness such as hepatitis, or a brain tumour in the absence of any identifiable high risk


Compulsions can be physical (behavioural) or mental (cognitive):

  • Physical/behavioural compulsions: washing, checking, rearranging, reassurance seeking
  • Mental/cognitive compulsions: mental rituals/review (“Did I actually do that obsession?”), replacing good thoughts with bad, counting, review

Common Compulsions

Washing Excessive hand-washing, showering, or cleaning activities
Checking Repeatedly turning the stove on and off; re-reading all emails to ensure content is appropriate; driving around the block to ensure didn’t hit someone; asking for repeated reassurance
Ordering Folding clothes “just so”, or arranging all cans in the cupboard so the labels are facing out
Counting Performing actions a certain arbitrary number of times, such as tapping each foot 4 times when getting out of bed
Repeating Repeatedly going up and down the stairs or flushing the toilet; typically done to “cancel” out a bad thought or until it feels “right”

What is the purpose of the compulsion in individuals with OCD?

  • Prevention seeking: “I want to stop something bad from happening.”
  • Reassurance seeking: “I need to know the bad thing didn't/will not happen.”

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
Florida Obsessive Compulsive Inventory (FOCI)
Rater Patient
Description A self-rated measure also used in monitoring OCD symptoms
DownloadFOCI 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
Florida Obsessive Compulsive Inventory (FOCI) Patient A self-rated measure also used in monitoring OCD symptoms FOCI Download

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] Other neuroanatomical structures include the orbitofrontal cortex, thalamus, and anterior cingulate gyrus.

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 pathophysiology of OCD is still being investigated. Some research has been shown that streptococcal throat infections are related to elevated risks of mental disorders, particularly OCD and tic disorders.[10] Criteria do currently exist for the diagnosis of PANDAS.[11]

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 characterized 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.[12] 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:[13]


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.[14] Several types of behaviourial principles to used to treat OCD.[15][16]

Education is Key!

OCD is a chronic mental disorder that can be difficult to treat. Therefore is it important to set realistic expectations as well as goals of treatment. Review the nature of the illness with your patient - that OCD is a chronic illness. Normalize the symptoms that your patients are experiencing. Realistic expectations include acknowledging that the OCD may not be cured, but that the goal is to improve function and reduce impairment. Those on medications need to understand that there is a lag time between medication initiation and response (up to 3 months). Those doing therapy need to understand there is extensive time commitment involved as well.


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).[17] Intravenous clomipramine has also been shown to be as effective, and if not more effective than SSRIs.[18] 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%).[19]

General Pharmacotherapy Principles for OCD

Treatment is long-term (> 1 year is recommended), can consider lowering dose after 3-6 months of treatment. Highest doses work the best, and it takes 6-8 weeks to see the improvements. Medications should be started at the usually dose and increased q5-7 days. Symptoms should be monitored via a scale like Y-BOCS. Focus of treatment should be for improvement, not remission. An adequate trial is 12-15 weeks, with at least 6 weeks at the maximum dose.

Medications should be discontinued very slowly with a slow taper. Relapse rates are very high unless the taper is combined with behavioural strategies! If the 1st line treatment is unsuccessful, at least 2 other medications (SSRI, SNRI, or clomipramine) should be tried. Augmentation is also another option.

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

Dosing for OCD

Medication Dose
Clomipramine 150-250mg PO daily[20]
Fluoxetine 20-80mg PO daily
Fluvoxamine 150-300mg PO daily
Sertraline 100-200mg PO daily
Paroxetine 20-80mg PO daily
Escitalopram 10-50mg PO daily*
Citalopram 20-80mg PO daily*

4. American Psychiatric Association: Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition. Arlington, VA, American Psychiatric Association, 2013.
16. Julien D, O’Connor KP, Aardema F, Todorov C. The specificity of belief domains in obsessive–compulsive symptom subtypes. Personality and Individual Differences. 2006; 41: 1205– 16.