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 1 to 2% and it is highly disabling. OCD symptoms (not meeting the diagnostic threshold) are on a variant of normal; thus OCD symptoms occurs in over 25% of adults, and developmentally appropriate rituals and superstitions are common in children. The incidence of OCD has two peaks (bimodal), with different gender distributions: the first peak occurs between ages 7-12 (males>females), while the second peak occurs in early adult hood, around age 21 (females>males).[1] Although males typically present at an earlier age compared to females (25% of males in childhood), close to 60% of overall OCD diagnoses are female.[2]


The initial onset of OCD is usually gradual, though acute onset is possible (but may warrant a more detailed neurologic work up). 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. With no treatment, the remission rates in adults are low (about 20% achieve remission in 40 years of follow up).[3] In pediatric populations, 41% remain symptomatic after 5 years.[4] Poor prognostic factors include: early onset, poor insight, schizotypal features, and thought/action compulsions.[5][6]


Individuals with OCD have 5 to 7% incidence for Tourette's, and up to 30% have a life-time history of tics.[7] Anywhere between 60-90% of individuals with OCD also have a comorbid mental disorder, including mood, anxiety, somatoform disorders, substance use disorders, psychotic disorders, and bipolar disorders. Many psychiatric and neuropsychiatric disorders also exist on the OCD spectrum (figure 1).[8] For example, the lifetime prevalence for depression in persons with OCD is 67%, and 25% will have social phobia.

Risk Factors

OCD has a strong neurobiologic basis and is highly heritable (half of all individuals have a family history of OCD; double the risk in those with a first degree relative and 10-fold risk if the relative's onset of OCD was in childhood or adolescence).[9] Environmental factors are also thought to play a role, including infectious etiologies and post-infectious autoimmune syndromes.

The OCD Spectrum (Adapted from Hollander, E. (1998). BJPsych, 173(S35), 7-12.) Fig. 1

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.[10]

  • 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

Insight Specifier

  • 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.


  • 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? (e.g. - worries about dirt/germs, or thoughts of bad things happening)
  2. Compulsions: Do you ever feel driven to do certain things over and over again? (e.g. - repeatedly washing hands, cleaning, checking doors or work over and over, rearranging things to get it just right, or repeating thoughts in your mind to feel better?)
  3. Does this waste significant time or cause problems in your life (Criterion B of DSM-5 criteria)? (e.g. - interfering with school, work, or seeing friends?)

Most individuals with OCD will have both obsessions and compulsions. Usually, a compulsion is performed in response to an obsession (e.g. - an obsession about thoughts of contamination, which leads to washing rituals; or an obsession about a situation being incorrect, which leads to a compulsion of repeating rituals until it feels “just right”). The goal of a compulsion is to reduce the distress triggered by the obsession, or to prevent a feared event from occurring (e.g. - getting sick, hurting someone). It is important to note that compulsions are not connected in a realistic way to the feared event (e.g., arranging items in a certain colour to prevent harm to a loved one) or are significantly excessive (e.g. - washing hands for 30 minutes at a time). Finally, the compulsions that are performed are not pleasurable, rather, they allow the individual to experience relief from their anxiety or distress.

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

Name Rater Description Download
Yale–Brown Obsessive Compulsive Scale (Y-BOCS) Clinician/Self-report A checklist and 10-item scale with severity rankings. It is the most widely used rating scale for OCD. Symptoms rated from 0 (none) to 4 (severe) in terms of: time spent, distress, resistance, control, and interference with functioning 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:

  • Caudate nucleus (located in the basal ganglia), is responsible for learning and memory (feedback), action selection, and integration with emotional information. Imaging studies have shown increased levels of activity during active symptoms, and activity levels normalize after successful treatment with medications or cognitive behaviour therapy.[11]
  • Orbitofrontal cortex, area responsible for decision-making, planning behaviours, reversal learning (i.e. - inhibiting old responses)
  • Thalamus, the brain's “switchboard”, which is “hard-wired” for primitive cleaning/checking behaviours.
  • Anterior cingulate gyrus, area of the brain responsible for error detection
  • Cortico-striatal-thalamo-cortical (CSTC) pathway, a neural circuit responsible for movement execution, habit formation, and reward) is also thought to be involved in OCD. There appears to be Hhyperactivity in this circuit in OCD[12][13]

There is some emerging evidence that second-generation antipsychotics, in particular clozapine and olanzapine, can cause de novo obsessive compulsive symptoms (not disorder) or exacerbate pre-existing symptoms.[14][15] Stimulant medications for ADHD may also exacerbate OCS or cause de novo symptoms.[16]

There is some evidence that streptococcal throat infections are related to elevated risks for mental disorders, particularly OCD and tic disorders.[17] This area of research remains controversial, but there are some proposed criteria for the diagnosis of PANDAS.[18]

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 also Criterion D of the DSM-5 diagnostic criterion.

  • Substance/Medication-induced obsessive compulsive symptoms (OCS)
    • Recent initiation of an atypical (second generation) antipsychotic that is temporally-linked to the symptoms.
    • Avoidant behaviors, recurrent thoughts, and the need for reassurance is also common in anxiety disorders. However these are usually real-life concerns, compared to the obsessions in OCD which usually do not involve real-life concerns (which may be odd/irrational). In addition, there are usually both compulsions and obsessions.
      • Similar to OCD, individuals with specific phobia may have a fear reaction to specific objects or situations. However, rituals are not present.
      • In social anxiety disorder (social phobia), the feared objects or situations are limited to social interactions, and avoidance or reassurance seeking is focused on reducing this social fear.
    • Rumination can occur in both OCD and depression. However rumination in depression is usually mood-congruent and not necessarily experienced as intrusive or distressing. Again, ruminations are not linked to compulsions, which is common in OCD.
    • In body dysmorphic disorder, obsessions and compulsions are limited to concerns about physical appearance
    • In trichotillomania, the compulsive behaviour is limited to only hair pulling and there are no obsessions
    • In hoarding disorder, the main symptoms are severe difficulty/distress in discarding one's possessions, and excessive accumulation of objects. However, if an individual has obsessions that are typical of OCD (e.g. - concerns about incompleteness or harm), and these obsessions lead to compulsive hoarding behaviors (e.g. - acquiring all objects in a set to attain a sense of feeling “just right” or not discarding books because they may contain information that could prevent harm), a diagnosis of OCD should be given instead.
    • In OCD, the obsessions and compulsions go beyond concerns about weight, body image, and food.
    • Some individuals with OCD will have very poor insight or even to the point delusional OCD beliefs. However, there will be obsessions and/or compulsions (thus ruling out delusional disorder) and an absence of other symptoms of schizophrenia or schizoaffective disorder such as hallucinations or thought disorder.
    • Tics are sudden, rapid, recurrent, nonrhythmic motor movement or vocalization (e.g. - blinking, throat clearing). A stereotyped movement is a repetitive, seemingly driven, nonfunctional motor behaviour (e.g. - head banging, rocking, biting). Tics and stereotyped movements are typically less complex than compulsions and they are not performed to neutralize obsessions. However, differentiating between complex tics and compulsions can sometimes be difficult. One way to distinguish is that compulsions are usually preceded by obsessions, whereas premonitory urges often precede tics. Since there is high comorbidity between the two disorders, there are cases were both diagnoses may apply.
    • Obsessive-compulsive personality disorder (OCPD) and OCD have similar sounding names, but are two distinct entities. There are no intrusive thoughts, images, urges or repetitive behaviors in OCPD. Individuals instead have long-standing, pervasive maladaptive patterns of excessive perfectionism and rigid control. However, it is possible to have both diagnoses.

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.[19] This is where clinical experience and good history taking comes in! Note also that children generally do not have good insight into their symptoms.[20]

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:[21]

Education is Key!

OCD is a chronic mental disorder that can be difficult to treat. Thus, whether you are treating with medications or psychotherapy, 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.

Medications or CBT?

CBT is very effective and safer and more long-acting than medications. However, it does require motivation and hard work. It may be difficult to do CBT is an individual has comorbidities or is dealing with other major stressors. CBT may also be difficult to access in certain areas. Medications are “easy” to take and does help in OCD, but its benefits are limited compared to CBT. Additionally, there are side effects to consider. Finally, the effects of medications are less enduring, and the risk of relapse is greater. See also: OCD Treatment Algorithm

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.[22] Several types of behaviourial principles to used to treat OCD.[23][24]

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CBT plus exercise exceeds typical effects of CBT for OCD. There is emerging evidence that exercise is a feasible and clinically impactful treatment for OCD.[25][26] The improvement in symptoms are hypothesized to be due to increased levels of brain-derived neurotrophic factor (BDNF), improved cerebral blood flow, increased volume to the hippocampus, enhanced cognitive and neuropsychological functioning, and improved resilience and overall well-being.

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).[27] Intravenous clomipramine has also been shown to be as effective, and if not more effective than SSRIs.[28] 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%).[29]

If First-line Drugs Aren't Working...

  • Switch: try at least 2 different SSRIs
  • Augment: with an antipsychotic
  • Consider other 2nd line agents
  • Other (off-label) augmentation strategies include:
    • Glutamate modulating agents: topiramate, riluzole, memantine
    • Mood Stabilizers: lithium, valproate, gabapentin (to enhance serotonergic neurotransmission)

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.

The length of treatment is typically long-term (i.e. - greater than 12 months). Dosage reduction can be considered 3-6 months after that. It is important to discontinue and taper the medication very slowly!! There are high relapse rates unless the taper is combined with behavioural strategies or CBT.

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[30]
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*

Treatment-refractory OCD that does not respond to CBT or medications may benefit from intensive residential treatment options.[31] Close to 70% experience significant improvement, and about 50% are asymptomatic by time of discharge.[32]

For children and adolescents, psychological treatments are generally preferred over pharmacotherapy. Fluoxetine is the most commonly used medication.[33] However, sertraline and fluvoxamine have also been found to be effective. In OCD, the addition of CBT in those with partial response to SSRIs is superior to SSRIs alone.[34]

Treatment-refractory pediatric OCD is defined as failing to achieve adequate symptom relief despite receiving an adequate course of cognitive-behavioral therapy (CBT) and at least 2 adequate trials of selective serotonin reuptake inhibitors (SSRI) (or clomipramine). When refractory, pharmacotherapy and outpatient CBT are often ineffective. Other biological therapies under investigation include Repetitive Transcranial Magnetic Stimulation (rTMS), deep brain stimulation, and psychosurgery.


Guideline Location Year PDF Website
Canadian Clinical Practice Guidelines Canada 2014 - Link
National Institute for Health and Care Excellence (NICE) UK 2005 - Link
American Psychiatric Association (APA) USA 2007 - Link
5) American Psychiatric Association: Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition. Arlington, VA, American Psychiatric Association, 2013.
7) American Psychiatric Association: Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition. Arlington, VA, American Psychiatric Association, 2013.
9) American Psychiatric Association. (2013). Diagnostic and Statistical Manual of Mental Disorders (5th ed.). Arlington, VA.
20) American Psychiatric Association. (2013). Diagnostic and Statistical Manual of Mental Disorders (5th ed.). Arlington, VA.
24) 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.