Side Effects of Haloperidol (Haldol)
Haloperidol carries significant risks of extrapyramidal symptoms (particularly in children and young adults), QT prolongation with potential for cardiac arrhythmias, and tardive dyskinesia with long-term use, along with neuroleptic malignant syndrome as a rare but potentially fatal complication. 1
Neurological Side Effects
Extrapyramidal Symptoms (EPS)
The most common and clinically significant adverse effects involve the extrapyramidal system, particularly with haloperidol as a high-potency typical antipsychotic 2, 3:
Acute Dystonia: Sudden spastic muscle contractions affecting the neck, eyes (oculogyric crisis), or torso. This occurs early in treatment, is more common in young males, and can be life-threatening if laryngospasm develops. Responds well to anticholinergic medications 2, 4.
Akathisia: Severe restlessness manifesting as pacing or physical agitation. Often misinterpreted as worsening psychosis or anxiety and is a major cause of medication noncompliance. Treatment is challenging—lowering the dose is preferred, though β-blockers and benzodiazepines may help 2.
Drug-Induced Parkinsonism: Bradykinesia, tremors, and rigidity that can be difficult to distinguish from negative symptoms of the underlying illness 2, 4.
Critical caveat: Children and adolescents may be at higher risk for EPS than adults 2. The elderly should avoid haloperidol when possible due to anticipated extrapyramidal symptoms 3.
Tardive Dyskinesia
A potentially irreversible syndrome of involuntary dyskinetic movements (tongue protrusion, facial grimacing, chewing movements, limb movements) that may appear during long-term therapy or after discontinuation 1. The risk is particularly elevated in:
- Elderly patients
- High-dose therapy
- Female patients
- Continuous use for 2+ years (50% risk in elderly) 3
There is no known effective treatment for tardive dyskinesia. Fine vermicular tongue movements may be an early warning sign—discontinuation at this stage may prevent full syndrome development 1.
Neuroleptic Malignant Syndrome (NMS)
A potentially fatal complication characterized by 1:
- Hyperpyrexia
- Muscle rigidity
- Altered mental status (including catatonic signs)
- Autonomic instability (irregular pulse/BP, tachycardia, diaphoresis, cardiac dysrhythmias)
- Elevated creatine phosphokinase, myoglobinuria, acute renal failure
Management requires immediate discontinuation of haloperidol, intensive symptomatic treatment, and medical monitoring. Recurrence has been reported with drug reintroduction 1.
Other Neurological Effects
- Seizures (grand mal)
- Confusion, vertigo, headache
- Insomnia, restlessness, drowsiness
- Exacerbation of psychotic symptoms including hallucinations 1
Cardiac Side Effects
QT Prolongation
Haloperidol causes mean QT prolongation of 7 milliseconds at usual doses 4. While this is relatively modest compared to other antipsychotics (thioridazine causes 25-30 ms prolongation), important considerations include:
- IV haloperidol carries FDA non-black box warning due to deaths associated with high doses and IV administration 4
- Intramuscular dosing is the preferred parenteral route in emergency settings 4
- Risk increases with: high doses, coadministration with other QT-prolonging medications, electrolyte abnormalities, cardiac disease 5
Recent systematic review evidence suggests that QT prolongation and torsades de pointes risk may be lower than historically feared, particularly at doses ≤5 mg, with recommendations for ECG monitoring only at higher doses 5.
Metabolic and Endocrine Effects
- Hyperglycemia, hypoglycemia, hyponatremia
- Lactation, breast engorgement, menstrual irregularities
- Gynecomastia, impotence, altered libido 1
Hematologic Effects
- Mild, usually transient leukopenia/leukocytosis
- Minimal decreases in red blood cell counts, anemia
- Agranulocytosis (rare) 1
Autonomic and Anticholinergic Effects
- Dry mouth, blurred vision
- Urinary retention
- Diaphoresis
- Priapism 1
Respiratory Effects
- Laryngospasm (rare but potentially life-threatening)
- Bronchospasm
- Increased depth of respiration
- Risk of bronchopneumonia (some fatal), possibly related to lethargy and decreased thirst sensation leading to dehydration 1
Dermatologic Reactions
- Maculopapular and acneiform skin reactions
- Photosensitivity (isolated cases)
- Hair loss 1
Hepatic Effects
Impaired liver function and/or jaundice have been reported 1.
Special Populations
Pregnancy and Neonates
Neonates exposed during third trimester are at risk for 1:
- Extrapyramidal symptoms
- Withdrawal symptoms (agitation, hypertonia, hypotonia, tremor)
- Respiratory distress and feeding disorders
- Some requiring ICU support and prolonged hospitalization
Reports exist of limb malformations with first-trimester exposure (though causal relationship not established) 1.
Elderly Patients
Should generally avoid haloperidol due to 3:
- Significant cholinergic, cardiovascular, and extrapyramidal side effects
- 50% risk of tardive dyskinesia after 2 years of continuous use
- Increased fall risk from somnolence, postural hypotension, and motor instability 1
Pediatric Patients
May have higher risk of extrapyramidal symptoms than adults and greater difficulty communicating concerns about side effects due to developmental issues 2.
Drug Interactions
Combined use with lithium has resulted in an encephalopathic syndrome (weakness, lethargy, fever, confusion, EPS, leukocytosis) followed by irreversible brain damage in some cases. Close monitoring required with prompt discontinuation if neurological toxicity appears 1.
Withdrawal Effects
Abrupt discontinuation may cause transient dyskinetic signs in patients on maintenance therapy, sometimes indistinguishable from tardive dyskinesia except for duration. Gradual withdrawal is recommended 1.
Comparative Safety Data
Recent geriatric emergency department systematic review found haloperidol associated with 16% overall adverse event rate (19/118 patients), with relatively lower rates compared to midazolam (53%) but similar to other antipsychotics 6. The 2023 systematic review in critically ill patients found haloperidol may reduce mortality with little change in serious adverse events compared to placebo, though results were not statistically significant 7.