Up to half of patients on clozapine develop obsessive-compulsive symptoms. Here’s how to manage it.
STUDY: Gürcan G et al, Prog Neuropsychopharmacol Biol Psychiatry 2026
STUDY TYPE: Review
FUNDING: Independent
Background
Clozapine is the most effective antipsychotic in schizophrenia, but is the antipsychotic most likely to cause OCD. This review summarizes the literature.
Summary
Between 20% and 76% of clozapine-treated patients develop obsessive-compulsive symptoms, with checking compulsions most common, followed by cleaning and counting rituals. Up to 46% develop these symptoms de novo (the other 54% had some preexisting OCD). About 69% of new cases appear within the first year, but symptoms can emerge as late as five years into treatment and often worsen over time.
The mechanism appears to involve clozapine’s blockade of serotonin receptors (5-HT2A and 5-HT2C), which disrupts the serotonin-dopamine balance in frontal-striatal circuits. Higher plasma levels carry greater risk, though some patients develop symptoms at moderate doses.
Obsessive-compulsive symptoms can be difficult to distinguish from psychotic symptoms. Obsessions are ego-dystonic and resisted; but patients don’t try to resist delusions. Symptoms that emerge after psychotic stabilization, following a dose increase, point toward clozapine as the cause.
Management depends on severity:
- Mild symptoms (Y-BOCS 8–15): psychoeducation, watchful waiting, possible dose reduction.
- Moderate symptoms (Y-BOCS 16–23): an SSRI, typically sertraline 100–200 mg, or adjunctive aripiprazole (those are evidence based for this side effect, but I’d consider ondansetron for its efficacy/tolerability or dextromethorphan, which has evidence in OCD and schizophrenia).
- Severe symptoms (Y-BOCS above 23): combined SSRI plus aripiprazole, cognitive behavioral therapy with exposure and response prevention, or antipsychotic switch.
Caution: Fluvoxamine and fluoxetine raise clozapine levels approximately 3-fold by inhibiting CYP1A2. Sertraline and escitalopram are preferred because they don’t. If you’re careful, however, fluvoxamine can improve clozapine’s tolerability by decreasing the metabolite, norclozapine.
Practice Implications
- Some disorders come with a strong feeling of secrecy and shame, so you have to ask directly about OCD, as well as trauma, suicidality, eating disorders, and substance use.
- Other symptoms are missed because they come with low insight, like psychosis and mania.
- Ask directly with a structured interview.
—Chris Aiken, MD
Director, Psych Partners
Editor in Chief, Carlat Psychiatry Report
