Antipsychotic Poisoning (Overdose)

What to do right now

1. Call 911 if the person is drowsy, unconscious, having a seizure, or breathing abnormally. Otherwise call Poison Control at 1-800-222-1222 (US). It is free, confidential and open 24 hours.
2. Do not make the person vomit. It can cause choking, especially in someone who is drowsy.
3. Place an unresponsive person on their side (recovery position) so they do not choke, and check their breathing.
4. Do not give food, drinks, coffee or other medicines to "wake them up".
5. Collect the medicine containers, including other medicines, alcohol and drugs that may have been taken, and note the time.
6. Stay with the person until help arrives. If it was intentional, remove other medicines and means of harm.

Symptoms can be delayed by several hours, especially with extended-release tablets such as quetiapine XR, so a person who seems fine still needs medical assessment.

How antipsychotics cause toxicity

Antipsychotics block dopamine receptors in the brain, which is how they treat psychosis. Most also block other receptors, and these explain most overdose effects:

Differences between drugs

• Quetiapine: one of the most common antipsychotic overdoses. Marked sedation, low blood pressure and fast heart rate. Large overdoses can cause coma needing a breathing tube.
• Olanzapine: sedation that can alternate with agitation, small pupils, slurred speech and a fast heart rate. Even one tablet can sedate a toddler.
• Clozapine: sedation, low blood pressure, heavy drooling and seizures.
• Risperidone and paliperidone: usually milder; low blood pressure and muscle spasms.
• Aripiprazole: generally mild in adults, though children can become drowsy and vomit.
• Haloperidol and other older "typical" drugs: muscle spasms and stiffness, QT prolongation and torsades. Thioridazine and chlorpromazine are especially toxic to the heart.
• Mixed drug overdoses with alcohol, benzodiazepines, opioids, antidepressants or lithium are more dangerous.

Symptoms of antipsychotic poisoning

• Drowsiness, slurred speech, unsteady walking, progressing to coma
• Low blood pressure, dizziness and fainting
• Fast heart rate
• Confusion, agitation or delirium
• Dry mouth, flushed skin, large or small pupils, urinary retention
• Muscle spasms of the neck, face, jaw or eyes (acute dystonia)
• Seizures
• Slow or shallow breathing
• Abnormal heart rhythms and cardiac arrest in severe cases
• Low body temperature, or high temperature with rigidity in neuroleptic malignant syndrome

Hospital assessment

• Vital signs and level of consciousness, with continuous heart monitoring
• ECG at arrival and repeated, to measure the QT and QRS intervals
• Blood tests: electrolytes (especially potassium and magnesium), glucose, kidney function, creatine kinase (muscle damage)
• Acetaminophen (paracetamol) and alcohol levels in any intentional overdose, because these are often also taken and are treatable
• Blood levels of most antipsychotics are not useful for treatment decisions

Treatment

There is no specific antidote. Treatment is supportive and very effective.

• Airway and breathing: oxygen, and a breathing tube with ventilator support for deep coma or poor breathing.
• Activated charcoal may be given if the person arrives within about 1 to 2 hours of a large overdose and can protect their airway.
• Low blood pressure: IV fluids first, then medicines such as norepinephrine if needed.
• Heart rhythm problems: correcting potassium and magnesium, IV magnesium for torsades, sodium bicarbonate for wide QRS complexes, and avoiding other drugs that lengthen the QT.
• Seizures and agitation: benzodiazepines.
• Acute dystonia: benztropine or diphenhydramine relieve spasms within minutes.
• Anticholinergic delirium: benzodiazepines, and sometimes physostigmine under toxicologist guidance.
• Observation: usually at least 6 hours with monitoring, and longer (often 12 to 24 hours) for extended-release products or when symptoms develop.

For a deliberate overdose, a mental health assessment is done once the person is medically stable, and a safety plan is made before discharge.

Outlook

Most people recover fully within 24 to 48 hours. Deaths are uncommon and usually involve large overdoses, older cardiotoxic drugs, mixed overdoses, or delayed treatment. Complications such as aspiration pneumonia, muscle breakdown from lying still for long periods, and injuries from falls can prolong recovery.

Prevention

• Store medicines locked and out of children's reach and sight, in original containers.
• Use pill organizers or blister packs if doses are easily confused.
• Do not restart clozapine at the full dose after missing more than 2 days. Contact your prescriber, because the dose must be built up again.
• Avoid mixing with alcohol, sedatives or opioids.
• If someone at home is at risk of self-harm, ask the pharmacist about smaller supplies and secure storage.

Frequently asked questions

What happens if you take too much quetiapine?

Quetiapine (Seroquel) overdose typically causes heavy sleepiness that can progress to coma, low blood pressure, dizziness and a fast heart rate. Large overdoses may need a breathing tube and blood pressure support. Effects can be delayed with extended-release tablets, so everyone should be assessed in hospital.

Is an antipsychotic overdose fatal?

It can be, but most people survive with prompt hospital care. The risk is higher with very large doses, older drugs such as thioridazine, mixed overdoses with alcohol or other sedatives, and delayed treatment. Calling 911 or Poison Control immediately is the most important step.

What should I do if my child swallowed an antipsychotic pill?

Call Poison Control at 1-800-222-1222 or 911 immediately, even if your child seems fine. A single adult tablet of some antipsychotics, such as olanzapine or quetiapine, can cause drowsiness or breathing problems in a small child. Do not make them vomit.

How long does an antipsychotic overdose last?

Most effects wear off within 24 to 48 hours, depending on the drug, the dose and whether it was extended-release. People are usually observed for at least 6 hours, and longer if symptoms develop or a long-acting tablet was taken.

Is there an antidote for antipsychotic poisoning?

No specific antidote exists. Treatment supports breathing, blood pressure and heart rhythm while the body clears the drug. Specific medicines treat complications, such as benztropine or diphenhydramine for muscle spasms, benzodiazepines for seizures, and magnesium for dangerous heart rhythms.