Mechanism of action
Propranolol competitively antagonizes both β1 and β2 adrenergic receptors throughout the body. It lacks intrinsic sympathomimetic activity and has no alpha-blocking properties.
β1 receptor blockade (cardiac effects)
By blocking β1 receptors in the heart, propranolol reduces heart rate (negative chronotropy), decreases force of contraction (negative inotropy), slows AV nodal conduction (negative dromotropy), and reduces automaticity. These effects lower cardiac output and myocardial oxygen demand. β1 blockade in the juxtaglomerular apparatus also decreases renin release, contributing to blood pressure reduction.
β2 receptor blockade (peripheral effects)
β2 antagonism causes bronchoconstriction by removing the bronchodilatory influence of endogenous catecholamines, which is particularly problematic in patients with reactive airway disease. β2 blockade also impairs peripheral vasodilation and can worsen peripheral vascular disease. In the liver, β2 blockade interferes with glycogenolysis and gluconeogenesis, potentially masking hypoglycemic symptoms in diabetics.
Additional properties
Propranolol has membrane-stabilizing (local anesthetic) effects at high concentrations, though this is clinically insignificant at therapeutic doses. Its lipophilicity allows significant CNS penetration, contributing to effects on tremor and migraine and potentially causing CNS side effects like vivid dreams and depression.
- Propranolol is a non-selective beta-blocker that antagonizes both β1 (cardiac) and β2 (bronchial, vascular) receptors
- Absolutely contraindicated in asthma and severe COPD due to β2-mediated bronchospasm risk
- Masks hypoglycemic symptoms (tachycardia, tremor) in diabetics by blocking adrenergic response; sweating remains
- Never use in pheochromocytoma without prior alpha-blockade (risk of hypertensive crisis from unopposed alpha stimulation)
- Lipophilic drug with high CNS penetration; effective for essential tremor, migraine prophylaxis, and performance anxiety
- Abrupt discontinuation causes withdrawal syndrome: rebound hypertension, tachycardia, angina, or MI; must taper gradually
- First-pass metabolism yields only 25-30% bioavailability; hepatic disease significantly increases drug effect
- Major drug interaction with verapamil/diltiazem: additive negative inotropic effects can cause severe bradycardia and heart block
Indications
Propranolol has multiple FDA-approved and off-label indications across cardiovascular, neurologic, and psychiatric conditions.
Cardiovascular indications
- Hypertension: Effective as monotherapy or combination therapy, particularly in younger patients
- Angina pectoris: Reduces myocardial oxygen demand by decreasing heart rate and contractility
- Arrhythmias: Controls supraventricular tachycardias, atrial fibrillation rate control, and ventricular arrhythmias
- Post-myocardial infarction: Improves survival when started early post-MI
- Hypertrophic obstructive cardiomyopathy: Reduces outflow tract obstruction
- Aortic dissection: Used with vasodilators to reduce shear stress
Neurologic indications
- Essential tremor: First-line agent for symptomatic relief
- Migraine prophylaxis: Reduces frequency and severity of attacks
Other indications
- Thyrotoxicosis: Controls adrenergic symptoms while treating underlying hyperthyroidism
- Portal hypertension: Reduces portal pressure and prevents variceal bleeding
- Performance anxiety: Off-label use for situational anxiety
- Pheochromocytoma: Used only after alpha-blockade is established
- Infantile hemangioma: Promotes regression of proliferating hemangiomas
Pharmacokinetics
Absorption and bioavailability
Propranolol is well absorbed after oral administration but undergoes extensive first-pass hepatic metabolism, resulting in bioavailability of approximately 25-30%. Food increases bioavailability. Peak plasma concentrations occur within 1-4 hours for immediate-release formulations.
Distribution
Propranolol is highly lipophilic and distributes widely throughout the body, including the CNS. It is approximately 90% protein-bound, primarily to alpha-1-acid glycoprotein and albumin. The volume of distribution is large, ranging from 3-5 L/kg.
Metabolism
Propranolol undergoes extensive hepatic metabolism via multiple pathways, including aromatic hydroxylation, N-dealkylation, and glucuronide conjugation. CYP2D6, CYP1A2, and CYP2C19 are involved in its metabolism. Several metabolites are active, including 4-hydroxypropranolol, though their clinical significance is limited. Genetic polymorphisms in CYP2D6 can affect drug levels.
Elimination
Less than 1% of propranolol is excreted unchanged in urine. Metabolites are eliminated primarily through renal excretion. The elimination half-life ranges from 3-6 hours for immediate-release formulations, necessitating multiple daily doses. Extended-release formulations allow once-daily dosing. Hepatic impairment significantly increases bioavailability and half-life.
Adverse effects
Cardiovascular effects
- Bradycardia: Excessive heart rate reduction, particularly problematic in patients with conduction abnormalities
- Hypotension: Orthostatic hypotension and reduced perfusion
- Heart failure exacerbation: Negative inotropic effects can precipitate or worsen heart failure
- AV block: Worsening of pre-existing conduction delays
- Peripheral vasoconstriction: Cold extremities, worsening of Raynaud phenomenon
Respiratory effects
- Bronchospasm: β2 blockade removes bronchodilation, potentially fatal in asthmatics
- Dyspnea: Even in patients without overt lung disease
Metabolic and endocrine effects
- Hypoglycemia masking: Blocks tachycardia and tremor of hypoglycemia; sweating may still occur
- Altered lipid profile: Increases triglycerides, decreases HDL cholesterol
- Hyperkalemia: Reduced cellular potassium uptake
Central nervous system effects
- Fatigue: Very common, dose-related
- Depression: Controversial but documented in susceptible individuals
- Sleep disturbances: Insomnia, vivid dreams, nightmares
- Dizziness: Particularly on standing
- Cognitive effects: Memory impairment, confusion in elderly
Other effects
- Sexual dysfunction: Erectile dysfunction, decreased libido
- Gastrointestinal: Nausea, diarrhea, constipation
- Skin reactions: Rash, alopecia, psoriasiform eruptions
Withdrawal syndrome
Abrupt discontinuation can cause rebound hypertension, tachycardia, angina, or myocardial infarction. Propranolol should be tapered gradually over 1-2 weeks when discontinuing, especially in patients with coronary artery disease.
Contraindications and warnings
Absolute contraindications
- Asthma or severe COPD: Non-selective β2 blockade can cause life-threatening bronchospasm
- Sinus bradycardia: Heart rate less than 50-60 bpm
- Second- or third-degree AV block: Without a functioning pacemaker
- Cardiogenic shock: Negative inotropic effects worsen hemodynamics
- Decompensated heart failure: Can precipitate acute decompensation
- Hypersensitivity to propranolol: Rare but documented allergic reactions
Relative contraindications and warnings
- Diabetes mellitus: Masks hypoglycemic symptoms and impairs recovery from hypoglycemia; use with caution and patient education
- Peripheral vascular disease: Can worsen claudication and reduce peripheral perfusion
- Pheochromocytoma: Must be given only after adequate alpha-blockade to prevent unopposed alpha stimulation
- Prinzmetal angina: May provoke coronary vasospasm
- Severe hepatic impairment: Reduced metabolism increases drug levels
- Thyrotoxicosis: Masks tachycardia but useful for symptom control; abrupt withdrawal can precipitate thyroid storm
- Myasthenia gravis: May worsen muscle weakness
- Raynaud phenomenon: Can exacerbate symptoms
Pregnancy and lactation
Propranolol is FDA pregnancy category C. It crosses the placenta and has been associated with intrauterine growth restriction, neonatal bradycardia, hypoglycemia, and respiratory depression when used near delivery. Use only when benefit outweighs risk. Propranolol is excreted in breast milk in small amounts; monitor breastfed infants for signs of beta-blockade.
Drug interactions
Pharmacodynamic interactions
- Calcium channel blockers (especially verapamil, diltiazem): Additive negative inotropic and chronotropic effects; risk of severe bradycardia, AV block, or heart failure
- Digoxin: Additive effects on AV nodal conduction; increased risk of bradycardia and AV block
- Antiarrhythmics (amiodarone, sotalol): Enhanced bradycardic and negative inotropic effects
- Clonidine: Paradoxical hypertension if propranolol is withdrawn first; discontinue propranolol several days before tapering clonidine
- Insulin and oral hypoglycemics: Masks hypoglycemic symptoms and prolongs recovery from hypoglycemia
- NSAIDs: Reduce antihypertensive efficacy by inhibiting prostaglandin-mediated vasodilation
- Epinephrine: Unopposed alpha stimulation can cause severe hypertension and bradycardia
Pharmacokinetic interactions
- CYP2D6 inhibitors (fluoxetine, paroxetine, quinidine, bupropion): Increase propranolol levels
- CYP1A2 inhibitors (ciprofloxacin, fluvoxamine): Increase propranolol levels
- CYP2C19 inhibitors (omeprazole, fluconazole): May increase propranolol exposure
- Rifampin: Induces metabolism, reducing propranolol levels
- Cimetidine: Decreases hepatic metabolism, increasing propranolol levels
- Aluminum hydroxide antacids: Decrease propranolol absorption
- Cholestyramine: Binds propranolol in gut, reducing absorption
- Phenobarbital: Induces metabolism, reducing propranolol efficacy
- Chlorpromazine: Both drugs inhibit each other's metabolism
Alcohol
Acute alcohol intake can increase propranolol levels by inhibiting metabolism, while chronic use may decrease levels through enzyme induction.
Clinical pearls
- Non-selective means β1 and β2: This is the key distinguishing feature from cardioselective beta-blockers like metoprolol or atenolol. The lack of β1 selectivity makes propranolol relatively contraindicated in asthma and COPD.
- Lipophilic CNS penetration: Unlike hydrophilic beta-blockers (atenolol, nadolol), propranolol crosses the blood-brain barrier readily. This explains its efficacy in essential tremor, migraine prophylaxis, and performance anxiety, but also increases risk of CNS side effects like nightmares and depression.
- Extensive first-pass metabolism: Bioavailability is only 25-30%, which means oral doses are much higher than would be predicted from IV doses. Hepatic dysfunction dramatically increases bioavailability and drug effect.
- Pheochromocytoma paradox: Never give propranolol (or any beta-blocker) before alpha-blockade in pheochromocytoma. β2 blockade removes vasodilatory effects, leaving unopposed alpha-mediated vasoconstriction, which can cause hypertensive crisis.
- Hypoglycemia masking in diabetics: Propranolol blocks the adrenergic symptoms of hypoglycemia (tachycardia, tremor, palpitations) but not diaphoresis, which is cholinergically mediated. Diabetic patients may not recognize dangerous hypoglycemia until severe neuroglycopenic symptoms appear.
- Withdrawal syndrome is real: Chronic beta-blocker use leads to upregulation of beta-receptors. Abrupt discontinuation can cause rebound hypertension, tachycardia, and precipitation of acute coronary syndromes. Always taper over 1-2 weeks.
- Essential tremor response predicts diagnosis: A dramatic response to low-dose propranolol strongly supports the diagnosis of essential tremor rather than parkinsonian or cerebellar tremor.
- Portal hypertension dosing differs: In portal hypertension for variceal bleeding prophylaxis, propranolol is dosed to achieve a heart rate reduction of approximately 25% from baseline, typically requiring higher doses than for other indications.
- Thyroid storm treatment: Propranolol is useful in thyroid storm not only for controlling adrenergic symptoms but also because it partially inhibits peripheral conversion of T4 to T3.
- Performance anxiety timing: For situational performance anxiety, propranolol is typically taken 30-60 minutes before the anxiety-provoking event to block the physical manifestations of anxiety (tremor, tachycardia, sweating).
PROPRANOLOL contraindications: Pheo (without α-block), Reactive airway disease (asthma/COPD), Obstructed heart (2nd/3rd degree block), Pump failure (decompensated HF), Really slow (bradycardia), Abrupt stop dangerous, No glucose awareness (masks hypoglycemia), Out cold (cardiogenic shock), Lipid soluble (CNS effects), Opposed alpha (with epinephrine), Liver metabolism (first-pass)
Practice questions
1. A 58-year-old man with type 1 diabetes mellitus is started on propranolol for hypertension. Two weeks later, his wife brings him to the emergency department after finding him confused and sweating profusely at home. His fingerstick glucose is 35 mg/dL. After treatment, the patient reports he did not experience his usual warning symptoms of hypoglycemia. Which of the following best explains why this medication masked his hypoglycemic symptoms?
2. A 45-year-old woman with newly diagnosed pheochromocytoma is being prepared for surgical resection. Her blood pressure is 180/110 mmHg and heart rate is 110 bpm. The surgical team requests medical optimization before surgery. Which of the following medication regimens is most appropriate for this patient?
3. A 62-year-old man with a history of coronary artery disease has been taking propranolol 80 mg twice daily for 3 years. He reads on the internet that beta-blockers cause fatigue and decides to stop the medication abruptly. Three days later, he presents to the emergency department with severe chest pain. ECG shows ST-segment elevations in leads V2-V4. Which of the following mechanisms best explains his presentation?
Frequently asked questions
How does propranolol work?
Propranolol works by blocking both β1 and β2 adrenergic receptors throughout the body. By blocking β1 receptors in the heart, it reduces heart rate, decreases contractility, and slows AV conduction, which lowers blood pressure and myocardial oxygen demand. β2 blockade affects bronchial smooth muscle, peripheral vasculature, and metabolic processes. Unlike cardioselective beta-blockers, propranolol's non-selective action affects multiple organ systems beyond the cardiovascular system.
What are the common side effects of propranolol?
Common side effects include fatigue, bradycardia, hypotension, cold extremities, and dizziness. CNS effects such as vivid dreams, insomnia, and depression can occur due to its lipophilic nature. Gastrointestinal symptoms like nausea and diarrhea are possible. Sexual dysfunction including erectile dysfunction may occur. The most dangerous side effect is bronchospasm in susceptible individuals, particularly those with asthma or COPD. Propranolol can also mask hypoglycemic symptoms in diabetics, making low blood sugar episodes harder to recognize.
Is propranolol a controlled substance?
No, propranolol is not a controlled substance in the United States or most other countries. It is a prescription medication classified as a beta-blocker used for various cardiovascular and neurological conditions. While it requires a prescription from a licensed healthcare provider, it does not have abuse potential and is not scheduled under the Controlled Substances Act. However, it should never be stopped abruptly due to risk of withdrawal syndrome.
Can propranolol be used in asthma patients?
Propranolol is absolutely contraindicated in patients with asthma or severe COPD. As a non-selective beta-blocker, it blocks β2 receptors in bronchial smooth muscle, which can cause potentially life-threatening bronchospasm. Even small doses can trigger severe respiratory distress in asthmatic patients. If beta-blocker therapy is essential in a patient with mild reactive airway disease, a cardioselective agent like metoprolol should be used instead, though even these must be used with extreme caution and close monitoring.
Propranolol vs metoprolol — what is the difference?
The key difference is selectivity: propranolol is non-selective (blocks both β1 and β2 receptors) while metoprolol is β1-selective, primarily affecting the heart. Propranolol is lipophilic and crosses into the CNS, making it effective for tremor, migraine, and anxiety but increasing CNS side effects. Metoprolol is more hydrophilic with less CNS penetration. Propranolol is contraindicated in asthma due to β2 blockade causing bronchospasm, while metoprolol can be used cautiously in mild lung disease. Both require tapering when discontinuing.
Conditions it is used for
Related drugs
Sources and further reading
DailyMed (FDA labels)StatPearls (NCBI Bookshelf)MedlinePlusWHO ATC/DDD index: C07AA05
Educational content for medical students, prepared by the WhiteCoat Pro editorial team with AI assistance; every page is reviewed by a second AI model for factual errors. It is not medical advice and does not replace the product label, local guidelines or a clinician.