Cholinergic Rebound in Clozapine Withdrawal

While withdrawal symptoms from typical antipsychotics are generally mild and self-limiting, clozapine discontinuation can trigger a severe clinical picture characterized by rapid-onset agitation, delirium, and psychosis. Research into three specific case reports highlights that these symptoms often manifest within days of stopping the medication. Patients may experience a clouding of consciousness, disorientation, and even physical complications like profuse diaphoresis, incontinence, and "word salad" speech. Notably, those with a history of tardive dyskinesia may also develop severe, uncontrollable choreoathetoid movements—slow, serpentine-like waving of the limbs and facial grimacing—that can be profoundly debilitating.

The underlying pathophysiology of this reaction is believed to be linked to "central cholinergic rebound". Because clozapine possesses extremely potent antimuscarinic activity, its abrupt removal can lead to a massive surge in cholinergic activity. This theory is supported by the fact that patients in the case reports showed rapid improvement when treated with benztropine, an anticholinergic, or upon resuming low doses of clozapine itself. Interestingly, substituting clozapine with risperidone did not prevent these symptoms in one patient, likely because risperidone lacks the necessary antimuscarinic properties to counteract the cholinergic surge.

To safely manage clozapine discontinuation, clinicians recommend a very gradual tapering process rather than abrupt cessation. In instances where the drug must be stopped quickly—such as in cases of medical necessity—the risk of severe withdrawal can potentially be mitigated by immediately substituting a psychotropic with high anticholinergic activity, such as thioridazine. Experience with subsequent patients suggests that adding such agents during the final weeks of a clozapine taper or immediately following an abrupt stop can effectively prevent the onset of delirium and psychotic relapse.

//https://www.psychiatrist.com/wp-content/uploads/2021/02/11814_clozapine-withdrawal-resulting-delirium-psychosis.pdf