Toxicology & Substance Use · Topic 13 of 17

Neuroleptic Malignant Syndrome

Toxicology · drug-induced hyperthermia

Neuroleptic Malignant Syndrome

A dopamine-blockade emergency: delirium, lead-pipe rigidity, fever and autonomic instability over days — stop the drug, cool, and support in the ICU.

Key numbers

Rigidity, fever, autonomic instability, deliriumT > 38 °C (often > 40)

Develops over days, usually first 2 weeksfirst 2 weeks

Worsening rigidity or fever: dantrolene, bromocriptinebromocriptine 2.5 mg q6–8h

01 · Defined byRigidity, fever, autonomic instability, delirium

NMS = altered mental status, generalized lead-pipe rigidity, hyperthermia (> 38 °C, often > 40 °C) and autonomic instability after a dopamine antagonist — DSM-5-TR requires exposure, or dopamine-agonist withdrawal, within 72 hours.

02 · DoStop the drug, cool, ICU care

Stop the causative drug, cool aggressively with physical measures, and give ICU supportive care — airway, fluids, electrolytes, blood pressure; some patients need intubation.

03 · GiveWorsening rigidity or fever: dantrolene, bromocriptine

For worsening rigidity or hyperthermia, add dantrolene IV, and restore dopamine tone with bromocriptine 2.5 mg PO/NG every 6–8 hours (maximum 40 mg/day) or amantadine; trial evidence for these adjuncts is limited.

Causes & risk factors

Why it happens

Any dopamine blocker, or stopping levodopaCauses: first- and second-generation antipsychotics, dopamine-blocking antiemetics (metoclopramide, prochlorperazine, promethazine, droperidol), and abrupt withdrawal of levodopa or dopamine agonists. Risk rises with high doses, rapid titration, parenteral use and switching agents.

Presentation

What you'll see

Develops over days, usually first 2 weeks must knowNMS usually begins in the first 2 weeks of treatment and develops over a few days, typically in order: mental status change first, then rigidity, hyperthermia and autonomic hyperactivity; reflexes are decreased.

Diagnosis & monitoring

Work-up

Elevated CK and leukocytosis support NMSSupporting labs: CK elevation (consensus criterion > 4 times the upper limit of normal) from rigidity, leukocytosis (often 10,000–40,000/mm³), and myoglobinuria; check electrolytes, BUN, creatinine, calcium and magnesium for complications.

Do right now

In this order

First moves

Stop the drug, cool, ICU care

→

Lorazepam 1–2 mg IV for mild rigidity, agitation

→

Worsening rigidity or fever: dantrolene, bromocriptinebromocriptine 2.5 mg q6–8h

Why each step

Stop the drug, cool, ICU careStop the causative drug, cool aggressively with physical measures, and give ICU supportive care — airway, fluids, electrolytes, blood pressure; some patients need intubation.

Lorazepam 1–2 mg IV for mild rigidity, agitationBenzodiazepines treat agitation and mild rigidity — lorazepam 1–2 mg IV or IM every 4–6 hours is the usual first-line drug in early, milder NMS; dexmedetomidine is an alternative for agitation.

Worsening rigidity or fever: dantrolene, bromocriptineFor worsening rigidity or hyperthermia, add dantrolene IV, and restore dopamine tone with bromocriptine 2.5 mg PO/NG every 6–8 hours (maximum 40 mg/day) or amantadine; trial evidence for these adjuncts is limited.

Management

Orders

Hypertension: clonidine or clevidipineTreat hypertension from autonomic instability with an alpha-2 agonist (clonidine) or a calcium channel blocker such as clevidipine.

Refractory NMS: consider electroconvulsive therapyElectroconvulsive therapy is an option for NMS refractory to supportive care and drug therapy.

Red flags & don'ts

Avoid harm

Rhabdomyolysis can need dialysis complicationRigidity causes rhabdomyolysis and AKI — correcting volume and electrolytes may require dialysis. Mortality in treated NMS is about 5% at 30 days and 15% at 1 year.

NMS or serotonin syndrome?

Commonly confused

Trigger	Dopamine antagonist or dopamine-agonist withdrawal
Onset	Over days
Neuromuscular	Lead-pipe rigidity
Reflexes	Decreased
Fever and rigidity	More severe

Commonly confused

Tell apart

Exclude infection and nonconvulsive status epilepticusRule out mimics: CNS infection and sepsis (neuroimaging, lumbar puncture — in NMS mental status and motor changes precede the fever), nonconvulsive status epilepticus (EEG), malignant hyperthermia and intrathecal baclofen withdrawal (history).

More detail

Reference

Show 4 reference facts

NMS develops in 0.1% or fewer of patients taking antipsychotics; it is idiosyncratic, not allergic, and can occur after years of therapy.

Atypical NMS may present without measured fever; rigidity precedes the fever in most patients, so treat new rigidity, altered mental status, autonomic instability and a rising CK as triggers for suspicion.

Amantadine for NMS: 100–200 mg initially, titrated to a maximum of 200 mg every 12 hours.

In patients with psychosis, early NMS is easily missed because the mental status change is dismissed as psychiatric.

Pearl

Lead pipe and slow: NMS rigidity builds over days after a dopamine blocker; serotonin syndrome clonus arrives within hours.

Sources · Merck Manual Professional — Neuroleptic Malignant Syndrome (Nov 2025) · Chen A, Bae M, et al. Lorazepam in Managing Atypical Neuroleptic Malignant Syndrome: A Systematic Review of Case Reports. West J Emerg Med 2025;26(5):1446–1453 · Özdemir F, Birtane D, et al. Intensive Care Management and Outcomes of Neuroleptic Malignant Syndrome: A Single-Center Retrospective Study. Medicina (Kaunas) 2026;62(2):378 · Andafa TW, Adekanmbi SA, et al. Early Recognition of Neuroleptic Malignant Syndrome Without Hyperthermia: A Narrative Review. Cureus 2026;18(8):e114485 · Merck Manual Professional — Serotonin Syndrome (May 2025) · Starter sheet built from the verified AGACNP fact map (facts reviewed 2026-10-15).