Obsessive - Compulsive Disorder (OCD)

OCD is best understood as a self-reinforcing cycle.

The two parts of OCD.

• Obsessions are recurrent, intrusive, unwanted thoughts, images or urges that the person finds distressing and hard to control (e.g. fear of contamination, of causing harm, a need for symmetry). They generate anxiety.
• Compulsions are repetitive behaviours (washing, checking, ordering) or mental acts (counting, praying) the person feels driven to perform, usually to neutralise an obsession or reduce the anxiety.

The cycle (this is the key idea):

1. An obsession intrudes →
2. it causes anxiety/distress →
3. the person performs a compulsion →
4. which brings temporary relief →
5. but the obsession returns, so the compulsion is repeated.

The relief at step 4 is what maintains OCD: it negatively reinforces the compulsion (removing anxiety), so the behaviour is strengthened and becomes hard to stop.

Diagnosis. Clinicians match symptoms to DSM-5/ICD-11: obsessions and/or compulsions that are time-consuming (often more than an hour a day) and cause significant distress or impairment. In DSM-5, OCD has its own category ('Obsessive-Compulsive and Related Disorders'). (See the [[schizophrenia]] note for the general diagnosis framework.)

Why this matters. The cycle explains the leading treatment: ERP deliberately breaks step 3–4 (you face the obsession but don't perform the compulsion), so the anxiety extinguishes on its own.

For a DSM-5 diagnosis of OCD:

• the presence of obsessions, compulsions, or both;
• they are time-consuming (e.g. take more than an hour a day) or cause significant distress/impairment;
• (in adults) there is often some insight that the obsessions/compulsions are excessive or unreasonable — though insight varies;
• the symptoms are not better explained by another disorder or by substances.

Common themes:

• Contamination obsessions → washing/cleaning compulsions.
• Harm/doubt obsessions → checking compulsions (e.g. locks, the cooker).
• Symmetry/order obsessions → arranging/counting compulsions.

Emotional and cognitive features: high anxiety, guilt and disgust; awareness that the behaviour is irrational yet an inability to resist it.

Genetic explanation. OCD runs in families: first-degree relatives are at higher risk, and twin studies show higher concordance in MZ than DZ twins — pointing to an inherited vulnerability (candidate genes affecting serotonin/dopamine systems). Concordance is not 100%, so genes are a predisposition, not destiny.

Neural explanation.

• Abnormal functioning in a brain circuit linking the orbitofrontal cortex (OFC), the basal ganglia (including the caudate nucleus) and the thalamus — a 'worry circuit' that fails to switch off, so intrusive thoughts and the urge to act persist.
• Serotonin — low serotonin activity is implicated (which is why serotonin-boosting drugs help).

Evidence. Brain-imaging shows heightened activity in this circuit; SSRIs (which raise serotonin) reduce symptoms.

Evaluation in brief. Scientific support and effective drug treatment, but reductionist (reduces OCD to genes/chemistry) and unclear on cause vs effect (abnormal brain activity could be a result of OCD); the success of SSRIs doesn't prove a serotonin cause.

Cognitive explanation. Everyone has intrusive thoughts, but people with OCD misinterpret them as highly significant and dangerous, and feel an inflated sense of responsibility to prevent harm. This catastrophic appraisal generates anxiety, which compulsions try to neutralise. The person also tends to overestimate threat and cannot tolerate uncertainty ('what if I didn't lock the door?'). This account underpins the cognitive part of CBT.

Behavioural explanation. Focuses on how compulsions are maintained: performing the compulsion reduces anxiety, and this relief negatively reinforces the behaviour, making it more likely next time (an operant-conditioning account that maps directly onto the OCD cycle). The person never learns the feared outcome wouldn't have happened, so the compulsion persists.

Evaluation in brief. The cognitive account explains why intrusive thoughts become obsessions and leads to effective CBT, but may describe maintenance rather than ultimate cause (which could be biological). The behavioural account explains the persistence of compulsions and justifies ERP, but is less good at explaining the obsessions themselves.

Biological treatment — SSRIs.

• SSRIs (selective serotonin reuptake inhibitors) block the reuptake of serotonin, increasing its availability and reducing obsessions/compulsions. (Often used at higher doses/longer than for depression.)
  • + Effective for many, easy to take, allow functioning. − Side effects, take weeks to work, treat symptoms not cause, relapse if stopped.

Psychological treatment — CBT with exposure and response prevention (ERP).

• The cornerstone therapy. The patient is exposed to the situation that triggers the obsession (e.g. touching a 'contaminated' surface) and then prevented from performing the compulsion (no washing).
• Because the compulsion is blocked, the anxiety rises and then naturally falls without it — the person learns the feared outcome doesn't occur and the negative-reinforcement cycle is broken (extinction). CBT adds challenging the catastrophic appraisals and inflated responsibility.
  • + Tackles the cause/maintenance, lasting benefits, no physical side effects. − Anxiety-provoking and demanding (drop-out), needs a motivated patient.

Key framing: SSRIs target the biochemistry; ERP breaks the behavioural cycle; combining medication with CBT/ERP is often the most effective approach.

Bring it together for Paper 3 'evaluate / discuss'.

Strengths

• Effective treatments (SSRIs, CBT/ERP) with strong evidence and a clear mechanism (breaking the cycle).
• Complementary explanations (biomedical + cognitive + behavioural) that map onto the cycle and the treatments.

Weaknesses / issues

• Reductionism — biomedical accounts reduce OCD to genes/chemistry; behavioural accounts may ignore biology.
• Cause vs effect — abnormal brain activity / low serotonin may be a result of OCD; cognitive appraisals may be maintenance not cause.
• Ethics / engagement — ERP is distressing (protection from harm; drop-out); drug side effects.

Relevant issues & debates

• Nature vs nurture / diathesis–stress — a genetic/neural vulnerability activated by stress and learned/cognitive factors.
• Reductionism vs holism — biology alone vs a bio-psycho-social view.
• Free will vs determinism — compulsions feel involuntary (determinism), yet ERP assumes patients can change behaviour.
• Application to everyday life — accessible, effective therapy (ERP, SSRIs).