Overdose of beta-blockers, calcium channel blockers and antipsychotics

Why heart pills and antipsychotics are dangerous in overdose, what the poisoning looks like and which antidote ideas hospitals use.

Updated Nov 12, 2026

Beta-blockers and calcium channel blockers are common, and in overdose they slow the heart and drop the blood pressure in ways that ordinary measures often fail to correct. Antipsychotic overdose is common too, mainly causing drowsiness, low blood pressure, heart rhythm changes and movement disorders. This page explains the mechanisms and the principles of treatment for learning; it gives no doses and is not a guide to treating a patient.

Key points

Both beta-blocker and calcium channel blocker overdose cause slow heart rate and low blood pressure; supportive care and early expert advice come first.
Propranolol is the most dangerous beta-blocker: it is fat-soluble and blocks sodium channels at high levels, causing seizures and a wide QRS.
Glucagon raises cAMP in heart cells without using beta receptors, which is why it helps in beta-blocker poisoning.
Calcium channel blocker overdose often raises blood sugar; intravenous calcium, high-dose insulin with glucose, vasopressors and, in refractory cases, extracorporeal support are used.
Most of these drugs are not removed by haemodialysis, and sustained-release tablets can cause delayed, prolonged toxicity.
Antipsychotic overdose causes sedation, low blood pressure, QT prolongation, seizures and dystonia; care is supportive. In Colombia, quetiapine is among the most frequent drugs in reported poisonings.

Beta-blocker overdose

At toxic levels beta-blockers lose any selectivity and block both beta-1 and beta-2 receptors. Slow heart rate and low blood pressure are the main signs, progressing to heart block, heart failure and shock. Propranolol is the most toxic: it enters the brain easily and also blocks sodium channels, like the tricyclic antidepressants, so seizures and a wide QRS complex can appear. Agents with partial agonist activity, such as pindolol, can paradoxically raise heart rate and pressure.

Treating beta-blocker overdose (principles)

Airway, breathing and circulation, cardiac monitoring and an ECG, and activated charcoal when the airway is safe and the ingestion recent.
Atropine, fluids and beta-agonists often fail, because the receptors are occupied.
Glucagon acts on its own receptor in heart cells and raises cAMP independently of beta receptors, improving heart rate and contraction.
Serious bradycardia may need temporary cardiac pacing; isoproterenol is an option for bradycardia and bronchospasm, while epinephrine can cause uncontrolled hypertension.
Propranolol is not significantly removed by dialysis.

Calcium channel blocker overdose

Calcium channel blockers can kill at relatively small overdoses. Verapamil and diltiazem act mostly on the heart, slowing the sinus node and AV conduction and weakening contraction; verapamil carries the highest death risk. Dihydropyridines such as nifedipine and amlodipine act mostly on blood vessels, causing vasodilation, low blood pressure and a reflex fast heart rate, but in massive overdose this selectivity is lost. Raised blood sugar is a recognised feature. Many products are sustained-release, so toxicity can be delayed and last a long time, and even mild cases are watched in hospital.

Treating calcium channel blocker overdose (principles)

Early gut decontamination with activated charcoal and, for sustained-release tablets, whole-bowel irrigation, before the drug-induced ileus sets in.
Intravenous calcium improves weak heart contraction but helps less with the vascular collapse.
High-dose insulin, with glucose supplements to keep blood sugar normal, is reported to help control the low blood pressure.
Vasopressors, glucagon, pacing, methylene blue and venoarterial ECMO for shock that does not respond; lipid emulsion has been reported in severe verapamil poisoning.
Calcium channel blockers are not removed by haemodialysis.

Antipsychotic overdose

Old (phenothiazines, butyrophenones) and new (atypical) antipsychotics can all cause central nervous system depression, seizures and low blood pressure. Some prolong the QT interval and can trigger dangerous arrhythmias. Potent D2 blockers such as haloperidol can cause acute dystonia and parkinsonism, and rarely neuroleptic malignant syndrome, with lead-pipe rigidity, fever and unstable blood pressure.

Treating antipsychotic overdose (principles)

Supportive care: airway protection in the drowsy patient, fluids for low blood pressure and cardiac monitoring for QT prolongation and arrhythmias.
Activated charcoal when the airway is safe and the ingestion recent.
Seizures are treated with intravenous benzodiazepines, as in other poisonings.
There is no specific antidote; dystonia and neuroleptic malignant syndrome are recognised and treated as complications.
Antipsychotics are not removed by haemodialysis.

Latin American context

In Colombia's 2024 national surveillance report on acute chemical poisoning, medicines were the most common group, mostly in suicide attempts; paracetamol (9.1%) and quetiapine (5.1%) were the most frequent drugs. The national toxicology line of the Ministry of Health (Línea Toxicológica Nacional) answers poisoning emergency calls from across the country.

Test yourself

Think of the answer, then tap the question to see it.

Why does glucagon help in beta-blocker overdose when beta-agonists often fail?

Glucagon acts on its own receptor in heart cells and raises cAMP without using the blocked beta receptors, so heart rate and contraction can improve.

Which beta-blocker is the most dangerous in overdose, and what extra effects does it cause?

Propranolol: it is fat-soluble and blocks sodium channels at high levels, so it can cause seizures and a wide QRS complex.

Which change in blood sugar is a recognised feature of calcium channel blocker overdose?

A rise in blood sugar; high-dose insulin with glucose is one of the treatments used for the low blood pressure.

Why is a patient who swallowed sustained-release verapamil watched for a long time even if well at first?

The tablets keep releasing drug, so toxicity can be delayed and prolonged; verapamil also carries the highest death risk in its class.

Which rare reaction to potent D2 blockers combines lead-pipe rigidity, high fever and unstable blood pressure?

Neuroleptic malignant syndrome, a medical emergency.

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Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given.

Sources: DailyMed - PROPRANOLOL HYDROCHLORIDE tablet (DailyMed (U.S. National Library of Medicine), 2026); Calcium-channel blocker overdose: MedlinePlus Medical Encyclopedia (MedlinePlus (U.S. National Library of Medicine), 2026); Informe de Evento 2024 Intoxicaciones Agudas por Sustancias Químicas (Instituto Nacional de Salud (Colombia), 2025).

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