Understanding Propranolol Overdose: Can Propranolol Cause Toxicity?

October 12, 2025 •

4 min read

Between 2012 and 2017, there was a 33% increase in deaths linked to propranolol overdose in the UK [1.2.2]. Yes, Can propranolol cause toxicity? is a critical question, as an overdose can rapidly lead to severe cardiovascular and neurological damage [1.2.1, 1.2.2].

Quick Summary

Propranolol, a nonselective beta-blocker, can cause significant toxicity if taken in overdose. Symptoms often appear within 2 hours and include severe low blood pressure, slow heart rate, and seizures.

Key Points

Toxicity is a Real Risk: Yes, propranolol can cause severe toxicity, especially in an overdose, which is considered a medical emergency [1.2.2].
Rapid Onset: Symptoms of toxicity, such as a severely slow heart rate and low blood pressure, typically appear within 2 to 4 hours of ingestion [1.2.1, 1.7.5].
Neurological Effects: Due to its ability to cross the blood-brain barrier, propranolol overdose can cause seizures, confusion, and coma [1.2.1, 1.2.4].
Variable Toxic Dose: The amount of propranolol that leads to an overdose varies, but ingestions over 1 gram are considered high risk [1.4.2, 1.2.5].
Risk Factors: Pre-existing heart or lung conditions, co-ingestion of alcohol or other depressants, and drug interactions increase the risk of toxicity [1.4.2, 1.9.3].
Emergency Treatment is Crucial: Immediate medical attention is vital. Treatment involves supportive care and specific antidotes like glucagon and high-dose insulin [1.3.6, 1.6.6].
Prevention Through Education: Patients should never exceed their prescribed dose and should be aware of the signs of overdose and potential drug interactions [1.4.3].

What is Propranolol?

Propranolol is one of the first beta-blockers developed and is used to treat a variety of conditions, including high blood pressure, angina (chest pain), irregular heartbeats, essential tremors, and even the physical symptoms of anxiety [1.2.1, 1.2.3]. It works by blocking certain nerve impulses, which slows the heart rate and makes it easier for the heart to pump blood throughout the body [1.2.3]. Propranolol is classified as a nonselective beta-blocker, and because it is highly lipophilic (fat-soluble), it can easily cross the blood-brain barrier, which contributes to its potential for central nervous system (CNS) effects in an overdose situation [1.2.1, 1.4.6].

Can Propranolol Cause Toxicity?

Yes, propranolol can cause significant and life-threatening toxicity, especially when taken in overdose [1.2.2]. It is recognized as one of the more challenging beta-blocker overdoses to treat due to its pharmacological properties [1.2.2]. An overdose of propranolol can cause rapid and severe chemical damage to the heart [1.2.2]. The drug's membrane-stabilizing activity can lead to sodium channel antagonism, which is responsible for CNS depression, seizures, and a widening of the QRS complex on an electrocardiogram (ECG) [1.2.1, 1.2.4]. The toxic dose can vary from person to person, but ingestions greater than 1-2 grams are associated with severe toxicity and seizures [1.4.2, 1.2.5]. Symptoms of toxicity typically manifest within two to six hours of ingestion [1.2.1].

Signs and Symptoms of Propranolol Toxicity

The clinical presentation of propranolol toxicity can range from mild to severe. It is crucial to seek immediate medical attention if an overdose is suspected.

Cardiovascular Effects:

Bradycardia: A significantly slow heart rate (less than 60 beats per minute) [1.2.4].
Hypotension: Dangerously low blood pressure, which can lead to shock [1.2.4].
Arrhythmias: Irregular heartbeats, including heart block and, in severe cases, cardiac arrest [1.2.2, 1.8.5].

Central Nervous System (CNS) Effects:

Seizures: More common with propranolol than other beta-blockers due to its high lipophilicity [1.2.1, 1.2.4].
CNS Depression: This can include drowsiness, confusion, delirium, reduced consciousness, and coma [1.2.1, 1.2.2].
Respiratory Depression: Difficulty breathing or slowed breathing [1.2.1].

Other Symptoms:

Nausea and vomiting [1.2.1].
Dizziness and fatigue [1.2.1].
Hypoglycemia (low blood sugar) [1.2.1].
Bronchospasm (especially in patients with asthma) [1.4.2].

Risk Factors for Toxicity

Several factors can increase an individual's risk of developing propranolol toxicity:

Dosage: Taking more than the prescribed dose is the primary cause. Accidentally double-dosing is a common mistake [1.4.3]. Doses as low as 1 gram can cause severe toxicity [1.4.2].
Co-ingestion of other substances: Combining propranolol with other cardiac depressants, alcohol, or CNS depressants increases the risk of severe symptoms [1.4.2, 1.9.3].
Underlying Health Conditions: Individuals with pre-existing conditions like heart disease, lung disease (asthma), liver or kidney problems, or diabetes are at a higher risk [1.2.3, 1.4.2].
Age: Elderly patients may be more susceptible due to slower drug metabolism [1.2.4].
Drug Interactions: Certain medications, including some antidepressants, antiarrhythmics, and NSAIDs, can alter propranolol levels in the body, increasing the risk of toxicity [1.4.3, 1.9.4].


Feature	Normal Side Effects	Propranolol Toxicity (Overdose)
Heart Rate	Mild slowing of heart rate.	Severe bradycardia (very slow heart rate) [1.2.4].
Blood Pressure	Mild lowering of blood pressure, potential dizziness [1.2.3].	Severe hypotension (very low blood pressure), shock [1.2.4].
Neurological	Fatigue, sleep disturbances, nightmares [1.2.3].	Seizures, confusion, loss of consciousness, coma [1.2.1, 1.2.2].
Breathing	Generally unaffected in healthy individuals.	Respiratory depression, difficulty breathing, bronchospasm [1.2.1, 1.4.2].
Onset	Can occur with initial doses but often mild and transient [1.2.3].	Rapid onset, usually within 2-4 hours of ingestion [1.2.2, 1.7.5].
Action Needed	Discuss with a doctor if persistent or bothersome [1.2.3].	Medical emergency. Call 999 or go to A&E immediately [1.2.3].

Treatment and Management

Propranolol overdose is a medical emergency requiring immediate hospitalization.

Emergency interventions may include:

Supportive Care: The primary approach involves stabilizing the patient, including securing the airway, providing breathing support (oxygen or ventilator), and administering intravenous (IV) fluids [1.3.2, 1.6.2].
Decontamination: Activated charcoal may be given to absorb the drug if the patient presents soon after ingestion [1.3.2, 1.6.5].
Medications: Specific antidotes and treatments are used to counteract the effects of the overdose. These include:
- Glucagon: Often considered a first-line antidote, it helps increase heart rate and contractility [1.3.6, 1.6.6].
- High-Dose Insulin Euglycemia Therapy (HIET): Used to improve myocardial contractility in severe cases [1.3.6].
- Vasopressors: Medications like epinephrine or norepinephrine are used to increase blood pressure [1.3.6].
- Benzodiazepines: Administered to control seizures [1.6.3].
- Sodium Bicarbonate: Used for certain ECG changes like a widened QRS interval [1.6.3].
Advanced Therapies: In cases of severe, treatment-resistant cardiogenic shock, advanced measures like extracorporeal membrane oxygenation (ECMO) may be necessary [1.3.6]. Hemodialysis is not effective for removing propranolol from the blood due to its high lipophilicity [1.6.4].

Conclusion

Propranolol is an effective medication for many conditions, but it carries a significant risk of toxicity and death when taken in overdose [1.2.2, 1.8.5]. Its ability to severely depress cardiovascular and central nervous system function makes an overdose particularly dangerous [1.2.2]. Patients should be educated on the importance of adhering to their prescribed dose, recognizing the early signs of toxicity, and understanding potential drug interactions. Any suspected overdose requires immediate emergency medical intervention, as prompt treatment is critical to improving the prognosis [1.8.5].

For more information on beta-blocker toxicity, you can review resources from the National Institutes of Health (NIH).

Frequently Asked Questions

Taking too much propranolol can be very serious. It can cause a dangerously slow heart rate, low blood pressure, seizures, breathing difficulties, and coma. It is a medical emergency that requires immediate attention [1.2.2, 1.2.3].

The toxic dose of propranolol varies between individuals. However, doses as low as 1 gram have been associated with severe toxicity, and ingestions over 2 grams are linked to a high risk of seizures and cardiovascular collapse [1.4.2, 1.2.5].

The earliest signs of overdose often appear within 2-4 hours and include profound bradycardia (slow heart rate), hypotension (low blood pressure), dizziness, and drowsiness. Seizures can also be an early sign [1.2.1, 1.7.5].

There are several treatments used. Glucagon is often considered the primary antidote. Other treatments include high-dose insulin euglycemia therapy (HIET), vasopressors to raise blood pressure, and benzodiazepines for seizures [1.3.6, 1.6.3].

Yes, death from propranolol overdose is possible and has been reported [1.2.2, 1.8.5]. It can result from severe hemodynamic collapse (shock), cardiac arrest, or other complications if not treated promptly [1.8.5].

Propranolol is more toxic due to its high lipophilicity, which allows it to easily enter the brain and cause seizures and coma. It also has membrane-stabilizing activity that blocks sodium channels, leading to severe cardiac effects [1.2.1, 1.2.5].

If you accidentally take a single extra dose, you might experience mild side effects like dizziness. However, you should not take another dose until the next scheduled time. If you take a significant overdose or feel unwell (e.g., very dizzy, slow heartbeat), you must seek immediate medical help [1.2.3, 1.4.3].