Obsessive-compulsive disorder (OCD) is a mental health condition marked by unwanted, intrusive thoughts (obsessions) and repetitive behaviors or mental acts (compulsions) performed to ease the anxiety they cause. Not Just Anxiety: OCD was reclassified out of the anxiety disorders in DSM-5 into its own category, reflecting a symptom pattern distinct enough to need separate diagnosis. The OCD Cycle: an intrusive thought triggers anxiety, a compulsion briefly relieves it, and that relief reinforces the ritual, guaranteeing it will run again. Prevalence: OCD affects roughly 2-3% of people at some point in their life, typically starting in the late teens. Brain Circuitry: imaging studies link OCD to a specific overactive brain loop involving the orbitofrontal cortex, caudate nucleus and thalamus. First-Line Treatment: exposure and response prevention (ERP), alone or with an SSRI, is the best-supported treatment, though its edge over other therapies is narrower than headline figures suggest. Genetics: a 2025 genome-wide study found OCD is highly polygenic, rooted in specific brain circuitry, and genetically overlaps with anxiety and depression. In the DSM-5, OCD was reclassified out of the anxiety disorders into its own category, Obsessive-Compulsive and Related Disorders. According to Jon Hershfield , MFT, author of The Mindfulness Workbook for OCD : “People describe for me that they are sort of reading this spam junk mail that’s coming into their feed marked as urgent and they don’t know if they are supposed to ignore it, or are they supposed to open it and reply to it, which then teaches the algorithm to send you more of that stuff.” OCD is thought to affect approximately 2-3% of the general population (Ruscio et al., 2010) and appears to be more common in women than men. The average age of the onset of OCD is 19 years old, with 25% of the cases being recognized by the age of 14. What Are Obsessions? Obsessions in OCD are unwanted, intrusive thoughts, images, or urges that cause intense anxiety and often center on feared outcomes. Abramowitz & McKay (2009) describe four key features: Recurrent, distressing thoughts, impulses, or images. Not simply excessive worries about everyday problems. Attempts to suppress, ignore, or neutralize them with other thoughts or actions. Recognition that they come from one’s own mind. Common obsessive thoughts might include: “What if I left the stove on and caused a fire?” “What if I harmed someone by accident?” “Did I say something offensive without realizing it?” “What if I get sick from touching this doorknob?” “If these books aren’t lined up perfectly, something bad will happen.” Even when people know these fears are irrational, the obsessions feel uncontrollable, time-consuming, and highly distressing. Trying to ignore or suppress them often makes the anxiety worse, which is why obsessions usually lead to compulsions. What Are Compulsions? Compulsions are repetitive behaviors or mental acts performed to reduce the distress caused by obsessions or to prevent something feared from happening. They can disrupt daily life and often provide only temporary relief. People may create personal rules or rituals , repeating actions until they feel “just right.” These behaviors are usually excessive or unrelated to the feared outcome (Abramowitz & McKay, 2009). Examples include: Washing and cleaning – excessive handwashing or cleaning objects. Checking – repeatedly ensuring doors are locked or appliances are off. Orderliness – arranging items symmetrically or in a specific order. Counting – repeating steps, numbers, or taps in patterns. Compulsions rarely bring pleasure but are performed to manage overwhelming anxiety. OCD does not have separate official diagnoses or subtypes. Instead, people often experience recurring themes in their obsessions and compulsions. These themes can overlap, shift over time, or appear in combination. Below are some of the most common presentations: Contamination and Cleaning : Fear of germs, dirt, or illness, leading to excessive handwashing , cleaning, or avoidance of certain places. Checking : Repeatedly ensuring doors are locked, appliances are off, or that no harm has been caused. Symmetry and “ Just Right ” : Intense discomfort if items aren’t aligned or arranged in a specific way, sometimes involving tapping, touching, or ordering rituals. Perfectionism : Strong need for exactness or things to feel “just right,” often linked with symmetry or order-related compulsions. Harm OCD : Distressing intrusive thoughts about harming oneself or others, often paired with reassurance-seeking or avoidance. Religious or Moral (Scrupulosity) : Excessive fears of sin, blasphemy, or moral failure, sometimes leading to repetitive prayers or rituals. Sexual Orientation or Relationship OCD (ROCD) : Obsessions around one’s sexual orientation or doubts about a relationship, often leading to compulsive checking of feelings or constant reassurance-seeking. Superstitious or Magical Thinking : Belief that certain actions, numbers, or rituals can prevent bad outcomes or bring good luck. Counting and Numbers : Urges to count objects, steps, or actions in specific ways or to a “safe” number. Real Event OCD : Preoccupation with past events, often replaying or questioning one’s morality or behavior. These themes do not cover every possible form OCD can take, but they show how intrusive thoughts and compulsions can attach themselves to different fears or concerns. What Causes OCD? A direct cause for the onset of OCD has not been found, and the condition’s causes are not fully understood. There are some theories for possible causes and risk factors that could make someone more likely to develop OCD. OCD appears to run in families. Someone with a parent who has OCD faces a higher risk of developing it themselves than someone with no family history of the disorder (Hettema et al., 2001). Coexisting conditions Other anxiety disorders (e.g., generalized anxiety disorder , social anxiety ) and mood disorders such as major depressive disorder, bipolar disorder are common alongside OCD (Ruscio et al., 2010). Some of the symptoms of these disorders, among others, may contribute to the development of OCD. Some cases have reported an acute onset of OCD within a day to a few months following traumatic brain injury (Berthier et al., 2001). Symptoms of OCD have also been associated with strokes, brain tumors, and Parkinson’s Disease (Kurlan et al., 2004). Serotonin levels Individuals with OCD appear to respond well to medication that affects the neurotransmitter serotonin (specifically, selective serotonin reuptake inhibitors, SSRIs). Because of this, it has been suggested that serotonin levels and how the brain processes this chemical are associated with OCD (Sinopoli et al., 2017). Brain Circuitry Brain-imaging studies point to a specific circuit. The orbitofrontal cortex flags that something is wrong, and normally the caudate nucleus of the basal ganglia filters this false alarm out before it reaches awareness. In OCD, the caudate under-performs. The signal loops back through the thalamus to the cortex uncorrected, so the brain keeps insisting something is wrong. The person keeps checking, washing or ritualising, trying to silence an alarm that will not switch off. Aim: The ENIGMA-OCD consortium (Boedhoe et al., 2017) tested whether people with OCD show reproducible brain-volume differences, and whether these differ between children and adults. Method: Structural MRI scans from 1,830 people with OCD and 1,759 healthy controls, across many research sites worldwide, were analysed using standardised protocols. Results: OCD was linked to reproducible volume differences in subcortical structures of this same circuit, and the pattern differed between children and adults. Conclusion: The scale of the study makes this far more reliable than any single small MRI study. But the differences are correlational, and cannot show whether the brain changes cause OCD, result from years of ritualising, or simply accompany it. Environmental factors Environmental factors, such as trauma, stress, and childhood adversity, may increase the risk of developing OCD (Boileau, 2011). For example, a history of childhood abuse, neglect, or other traumatic events may contribute to the development of OCD symptoms later in life. Cognitive factors Cognitive factors , such as dysfunctional beliefs and thought patterns, may contribute to the development and maintenance of OCD. For example, having a heightened sense of responsibility, a need for certainty, or a tendency to catastrophize may contribute to obsessive thoughts and compulsive behaviors. As Professor Paul Salkovskis , the Oxford clinical psychologist who originated this theory (Salkovskis, 1985, 1999), explains, OCD is best understood as a disorder of over-conscientiousness, not strange thinking. In a 2022 University of Oxford webinar, he described people with OCD as, in his words, “too careful, too nice, and trying too hard.” On his account, intrusive thoughts themselves are normal and near-universal. The problem is treating an ordinary thought as a warning that demands action, which is precisely the belief that exposure-based CBT aims to change. A related idea is thought-action fusion (Rachman, 1993): treating a thought as if it were equivalent to the act itself. Believing that picturing a plane crash makes the crash more likely is one example. The thought now feels intolerable. So the person feels compelled to undo it, but suppressing an unwanted thought tends to backfire and bring it back more often. Learned behaviors Learned behaviors, such as engaging in compulsive behaviors as a way to reduce anxiety or distress, may reinforce the cycle of obsessions and compulsions. Likewise, if someone has observed their parent engaging in compulsions, a child may learn that this is typical behavior and may be more likely to exhibit these behaviors themselves. This still leaves an open question: how do compulsive rituals get started in the first place? One classic experiment, run in a Skinner box , offers a possible answer. Aim: Skinner (1948) tested whether a reward delivered by pure chance, with no real link to behavior, could still create and maintain a repetitive ritual. Method: Hungry pigeons received food at fixed time intervals regardless of what they were doing at that moment. Results: Most birds developed their own repetitive “ritual,” such as turning in circles or bobbing their head, based on whatever they happened to be doing when food first arrived. Conclusion: A purely accidental link between behavior and reward can create and sustain a ritual. This is a plausible model for how a compulsion might start by chance, though it says nothing about the intrusive thoughts that drive human OCD. How OCD Can Affect Daily Life, Work & Relationships 1. Disruption to Daily Routines & Self-Care Time: Obsessions and compulsions may take up hours each day, leaving less time for normal tasks like getting ready, cooking, cleaning, or errands. Self-care can suffer: sleep may be disturbed; hygiene routines may become ritualised; individuals might avoid certain places or people because of fear/contamination or intrusive thoughts. Home environment: rituals or checking interfere with managing chores, organizing, or maintaining a home in a way that feels manageable. 2. Effects on Work, School, or Productivity Reduced work performance: time spent on compulsions or intrusive thoughts can reduce concentration, slow down tasks, and lead to missed deadlines. Avoidance: people with OCD may avoid tasks, projects, meetings, or social interactions at work/school because they trigger obsessions or compulsive rituals. This can limit responsibilities or opportunities. Decision paralysis or over-checking: due to doubt or fear of making a mistake, people might excessively check work or rework things, delaying completion. Absenteeism or job instability: stress, burnout, or inability to keep up with work demands can lead to calling off work more often or problems sustaining employment. “You lose time. You lose entire blocks of your day to obsessive thoughts or actions. I spend so much time finishing songs in my car before I can get out or redoing my entire shower routine because I lost count of how many times I scrubbed my left arm.” 3. Strain on Relationships & Social Life Social isolation: Individuals may avoid social events or interactions due to fear of embarrassment, intrusive thoughts, or rituals that make participation difficult. Communication difficulties: They may find it hard to explain their behavior or thoughts; loved ones may not understand; reassurance-seeking or repeated checking can frustrate others. Emotional strain: OCD contributes to feelings of guilt, shame, or low self-esteem. The person with OCD may feel helpless, and partners, family, or friends may feel frustrated, burdened, or unsure how to help. Relationship dynamics change: Rituals may involve others (asking them to do certain things, avoid things, accommodate compulsions). This can lead to resentment and misunderstanding. 4. Impact on Quality of Life & Emotional Well-Being Emotional toll: increased anxiety, depression, and general distress are common, and the ongoing cycle of obsessions and compulsions causes emotional exhaustion. Sleep disturbances, fatigue, and health effects: stress and disruptiveness of symptoms affect rest, mood, and energy. Also, some compulsive behaviors can cause physical harm (e.g., skin damage from excessive washing), or avoidant behaviors may lead to neglected health. Reduced life satisfaction: people with OCD often report lower quality of life, less enjoyment in daily activities, and restricted participation in hobbies/social life. “OCD is like having a bully stuck inside your head and nobody else can see it.” How is OCD portrayed in media versus reality? Media often shows OCD through exaggerated stereotypes: excessive cleanliness, organisation, or quirky perfectionism (think: germ phobia, lining up items exactly). Characters are frequently defined by visible compulsions, used for comedic effect, or shown as strange or odd in a way that oversimplifies the disorder. In reality, OCD is much more complex. Many people’s obsessions are internal (intrusive thoughts about harm, morality, doubt, taboo topics) rather than about cleanliness or order. Compulsions can be mental acts, invisible to others, and the distress from obsessions is often overwhelming even when actions don’t “look” dramatic. These misrepresentations can perpetuate stigma, make people feel their experiences don’t count, delay recognition, and discourage seeking help. Embracing Uncertainty with OCD Uncertainty is an inherent part of life. Yet, for those with OCD, uncertainty can become an obsession in and of itself. Intrusive thoughts may latch onto a specific fear or doubt, analyzing the endless possibilities of an uncertain situation or future. This only fuels anxiety and dysfunction. The good news is there are effective approaches to better cope with uncertainty when you have OCD: Acknowledge Nothing is Truly Certain It can be helpful to take a step back and acknowledge the deeper truth: very little in life is actually 100% knowable or certain. The obsession around a specific intrusive thought or fear is usually not about the content itself, but rather the outcome being uncertain. “I often find that once I pinpoint or realize the power that I’ve been allowing a particular obsession to hold, it is much easier to dismiss it.” Reframe Thoughts Around the Fear of Uncertainty Rather than analyzing the specific “what if” content, recognize the underlying fear is likely tied to uncertainty in that moment. For example, an intrusive thought like “what if I lose control?” is not really about the specifics of losing control. It is about the uncertainty of not knowing whether that could happen. Reframing intrusive thoughts to focus more on the fear of uncertainty can help reduce rumination. Share Your Thoughts and Realize You’re Not Alone Writing down intrusive thoughts and seeing examples of how common various themes are can provide immense relief. Online groups even allow for anonymity. Realizing others have very similar thoughts and fears around uncertainty helps reinforce that these thoughts are symptomatic of OCD, not a reflection of oneself or reality. There is power in exposing thoughts to the light and seeing we don’t suffer alone. While certainty may remain elusive, there are healthy, compassionate ways for those with OCD to better cope with uncertainty. Reframing fearful thoughts and finding community can help transform uncertainty from an enemy into simply a part of living. “One method which has helped me is just observing the voice with non-judgement and then internally labelling it as thinking and then taking a deep breath.” The science writer David Adam, an editor at Nature , has lived with OCD for two decades. He describes his experience in his 2014 memoir, The Man Who Couldn’t Stop: OCD and the True Story of a Life Lost in Thought . His own obsession centred on a fear of contracting HIV, with a single doubt about ordinary contact expanding until it colonised his daily life. The fear rarely made sense.

As Adam explains, what distinguishes OCD is not having intrusive thoughts, since almost everyone has them, but the inability to dismiss them. His own recovery came through confronting the fear directly and accepting uncertainty, rather than chasing the impossible certainty his obsession demanded. Treatment Options Treatments for the symptoms of OCD depend upon the symptoms experienced and the extent that they affect the individual’s life and overall functioning. Treatment for OCD is highly individualized: what works for one person may not work for another. Exposure and response prevention (ERP) Exposure and Response Prevention ( ERP ) is considered a first-line, gold-standard therapy for OCD. It works by helping people gradually confront their fears (exposures) while resisting compulsive behaviors (response prevention), under a therapist’s guidance. Over time, this helps reduce anxiety, break the cycle of obsession → compulsion → relief, and teach that feared outcomes often don’t happen—or are tolerable. Key techniques include: Building an exposure hierarchy (from least to most distressing situations). Using in vivo exposure (real‐life situations) or imaginal exposure (thoughts or images) when real exposure isn’t feasible. Delaying or modifying compulsions instead of immediately giving in. Psychoeducation: learning about how OCD works, what maintains it, and why facing fears helps. Effectiveness: Two major meta-analyses quantify how well ERP and CBT work. Öst et al. (2015): pooling 37 randomised controlled trials, CBT showed very large effects against waiting-list (1.31) and placebo (1.33) controls, and outperformed medication alone (0.55). Reid et al. (2021): across 36 RCTs, ERP showed a large overall effect against controls (g = 0.74). But allegiance mattered: the effect shrank to near zero against other active therapies (g = -0.05) once researcher allegiance was accounted for. Reading the two together: ERP is genuinely effective and outperforms doing nothing, but its advantage over other well-run therapies is narrower than headline figures suggest. Cognitive Behavioral Therapy (CBT) In addition to ERP, CBT can help people challenge and reframe obsessive thoughts. With a therapist’s guidance, individuals examine evidence for and against their fears, identify unhelpful thinking patterns, and learn healthier ways to respond. CBT can help reduce reliance on rituals by building more balanced and realistic perspectives. Mindfulness teaches people to notice intrusive thoughts and uncomfortable feelings without judgment. Instead of struggling to suppress or label them as “bad,” mindfulness encourages seeing them as temporary mental events. This shift can reduce the cycle of fear and compulsion and is often used alongside ERP. Selective serotonin reuptake inhibitors (SSRIs) such as fluoxetine, sertraline, fluvoxamine, and paroxetine are commonly prescribed and may reduce OCD symptoms. Medication often works best in combination with CBT or ERP, especially for moderate to severe OCD, and should only be considered after discussion with a medical professional. Psychodynamic Therapy Psychodynamic therapy explores unconscious thoughts and past experiences that may influence OCD. While it may provide insight for some, research evidence is limited, and major guidelines (NICE, 2006) do not recommend it as a primary treatment. Lifestyle changes Certain lifestyle changes can also be beneficial in managing OCD symptoms on one’s own . Here are some examples: Improved sleep hygiene: Establishing a consistent sleep routine and creating a relaxing bedtime routine can promote better sleep, which may help manage OCD symptoms. Stress management : Learning effective stress management techniques, such as deep breathing or mindfulness , can help cope with stress and reduce OCD symptoms. Regular exercise: Engaging in regular exercise can help regulate mood and provide a healthy outlet for managing OCD symptoms. Healthy diet: Eating a balanced and nutritious diet can support overall mental health and help manage OCD symptoms. Time management: Effective time management, such as creating a schedule or to-do list, can reduce stress and contribute to better OCD symptom management. Avoidance of substance abuse: Avoiding or minimizing substance abuse can be important in managing OCD symptoms effectively. Lifestyle changes alone may not be enough to manage OCD, but they can complement other treatments and support overall mental well-being. Critical Evaluation of OCD Explanations No single theory explains OCD on its own. Here are the main criticisms raised about the leading explanations: No Explanation Stands Alone: the behavioral model explains how rituals continue but not where intrusive thoughts start, and biology maps vulnerable circuits, not their content. The Treatment-Aetiology Fallacy: that SSRIs relieve OCD is often taken as proof that low serotonin causes it, but a drug relieving a symptom does not reveal its cause. Correlational Neuroscience: brain-imaging differences are associations, not proven causes, and cannot show whether altered circuitry causes OCD or merely results from years of ritualising. Allegiance in the Therapy Evidence: even ERP’s own evidence base is weaker once researcher allegiance and study quality are accounted for. Heterogeneity: OCD covers such different presentations that findings from one group of patients may not generalise to another. No Single Explanation Is Sufficient No account works alone. The behavioural account, built on Mowrer’s two-process theory, explains how a ritual is maintained once it starts: an action that happens to reduce anxiety gets reinforced and repeats. It says far less about why intrusive thoughts arise in the first place. The cognitive account fills that gap. Salkovskis (1985, 1999) and Rachman (1993) show how ordinary intrusive thoughts get misread as signs of personal responsibility or moral danger. But why only some people misread them this way is unclear. Biology may explain why. The biological and neuroanatomical models describe a vulnerable fronto-striatal circuit, yet cannot explain the specific content of an obsession. The most defensible reading combines all three: inherited vulnerability, expressed through learning and cognitive style, the same diathesis-stress logic used for schizophrenia and depression. The Treatment-Aetiology Fallacy This pattern has a name: the treatment-aetiology fallacy. SSRI efficacy is often treated as evidence that low serotonin causes OCD, but a drug that relieves a symptom does not always have to target its root cause. Only drugs that raise serotonin relieve OCD, and antidepressants without strong serotonergic action are largely ineffective. Clomipramine, the first drug shown to relieve OCD, is also a potent serotonin reuptake inhibitor. That specificity is real evidence for a serotonergic link. An aspirin relieves a headache without a lack of aspirin having caused it. OCD needs higher SSRI doses than depression, and gets only a partial response even then. That gap matters. The serotonin story is incomplete on its own, and glutamate and dopamine systems matter too. SSRI response identifies one chemical lever on OCD, not its underlying root cause. Correlational Neuroscience Scale is not everything. Even the largest neuroimaging study of OCD to date, the worldwide ENIGMA-OCD consortium (Boedhoe et al., 2017; see Brain Circuitry above), only establishes correlation, not cause. A brain-volume difference cannot reveal whether it causes OCD, results from years of ritualising, or simply travels alongside it. Framing OCD as a pure “brain disorder” risks obscuring the appraisal-driven pattern the cognitive model captures, and that is exactly what makes psychological treatment work. The neuroimaging evidence maps a vulnerable circuit. It does not, on its own, explain why the circuit misfires in some people and not others. This does not overturn the biological account. It means the finding should be read as evidence of a vulnerable circuit, not proof of what causes OCD. Allegiance and Quality in the Therapy Evidence Even OCD’s gold-standard therapy is not immune to publication bias. Reid et al. (2021) asked whether trials of cognitive-behavioural therapy with exposure and response prevention (ERP) reported bigger effects when the research team itself favoured the therapy. Trials with suspected researcher allegiance reported a large effect against controls (g = 0.95), a result that looked highly convincing on its face. The eight trials without any suspected allegiance found ERP was not significantly more effective than the comparison condition (g = 0.02). This does not overturn ERP’s first-line status. The wider evidence, covered under Exposure and response prevention (ERP), still favours it overall. But confidence in any single trial should track its rigour and independence, not its authors’ enthusiasm. A well-run, allegiance-free trial remains the real test of any therapy. OCD looks very different from person to person. Two people with the same diagnosis may share almost no symptoms: one may wash compulsively, another may silently repeat prayers, and a third may endlessly check locks. Researchers have tried to sort this variety into clean subtypes, but attempts to validate hard categorical subtypes have largely failed. The variety is real. Contemporary research favours a dimensional model instead, treating contamination, checking, symmetry, taboo intrusions and scrupulosity as overlapping themes rather than separate diagnoses. The practical consequence is that group-level findings, whether from a treatment trial or a large brain-imaging study, may not generalise to any single patient. A diagnosis this varied may, in the end, be bundling together several quite different problems under one name. Contemporary Research Scale is now the norm. OCD research has entered the era of very large, multi-site studies. The clearest example is the largest genetic study of OCD ever conducted. Aim: Strom et al. (2025) set out to find the genetic variants that raise OCD risk, estimate heritability, and identify the genes and brain cell types most likely involved. Method: A genome-wide association study pooled data from 53,660 people with OCD and over two million controls across international research cohorts. Results: The study found 30 genome-wide-significant genetic locations and identified 249 candidate genes. Genetic risk was concentrated in neurons of the hippocampus, cortex, and striatum, the same circuit implicated by brain imaging. Conclusion: OCD is highly polygenic and rooted in identifiable brain circuitry, sharing genetic risk with anxiety, depression and related conditions. This converges with the imaging evidence (see Brain Circuitry above), though most participants studied were of European ancestry. Treatment research has moved the same way. 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Journal of Experimental Psychology, 38 (2), 168-172. https://doi.org/10.1037/h0055873 Strom, N. I., Gerring, Z. F., Galimberti, M., Yu, D., Halvorsen, M. W., Abdellaoui, A., Rodriguez-Fontenla, C., Sealock, J. M., Bigdeli, T., … Mattheisen, M. (2025). Genome-wide analyses identify 30 loci associated with obsessive-compulsive disorder. Nature Genetics, 57 (6), 1389-1401. https://doi.org/10.1038/s41588-025-02189-z Walsh, K. H., & McDougle, C. J. (2011). Psychotherapy and medication management strategies for obsessive-compulsive disorder. Neuropsychiatric disease and treatment , 485-494. Further Information Grupe, D. W., & Nitschke, J. B. (2013). Uncertainty and anticipation in anxiety: an integrated neurobiological and psychological perspective. Nature Reviews Neuroscience, 14(7), 488-501. https://www.psychiatry.org/patients-families/obsessive-compulsive-disorder/what-is-obsessive-compulsive-disorder Saul McLeod, PhD BSc (Hons) Psychology, MRes, PhD, University of Manchester Chartered Psychologist (CPsychol) Saul McLeod, PhD, is a qualified psychology teacher with over 18 years of experience in further and higher education. He has been published in peer-reviewed journals, including the Journal of Clinical Psychology. Olivia Guy-Evans, MSc Associate Editor for Simply Psychology BSc (Hons) Psychology, MSc Psychology of Education Olivia Guy-Evans is a writer and associate editor for Simply Psychology, where she contributes accessible content on psychological topics. She is also an autistic PhD student at the University of Birmingham, researching autistic camouflaging in higher education.