Mechanism of action
Nortriptyline inhibits the reuptake of norepinephrine and, to a lesser extent, serotonin at presynaptic nerve terminals in the central nervous system. By blocking the norepinephrine transporter (NET) and serotonin transporter (SERT), it increases synaptic concentrations of these monoamines, enhancing neurotransmission in mood-regulating pathways.
As a secondary amine TCA, nortriptyline exhibits greater selectivity for norepinephrine reuptake inhibition compared to tertiary amine TCAs like amitriptyline. This selectivity accounts for its slightly better tolerability profile. Nortriptyline also blocks multiple receptors including histamine H1, muscarinic cholinergic, and alpha-1 adrenergic receptors, which contribute to its side effect profile.
The active metabolite of amitriptyline is nortriptyline, formed via demethylation. The antidepressant effect requires several weeks of treatment, reflecting adaptive changes in postsynaptic receptor sensitivity rather than immediate synaptic effects.
- Nortriptyline is a secondary amine TCA with a therapeutic window of 50-150 ng/mL requiring drug level monitoring
- Secondary amines (nortriptyline, desipramine) have fewer anticholinergic effects than tertiary amines (amitriptyline)
- Black box warning: increased suicidal ideation risk in patients under 25 years old
- TCA overdose triad: altered mental status, seizures, and wide QRS complex; treat with sodium bicarbonate
- Contraindicated with MAOIs (14-day washout required) due to risk of hypertensive crisis and serotonin syndrome
- Nortriptyline is the active metabolite of amitriptyline formed by demethylation
- Effective for neuropathic pain at lower doses than required for depression
- CYP2D6 metabolizes nortriptyline; inhibitors like fluoxetine significantly increase drug levels
Indications
Nortriptyline is FDA-approved for the treatment of major depressive disorder. It is particularly useful in patients who have not responded to newer antidepressants or who have comorbid chronic pain conditions.
Off-label uses include:
- Neuropathic pain: Diabetic neuropathy, postherpetic neuralgia, and other chronic pain syndromes
- Migraine prophylaxis: Reduces frequency and severity of migraine headaches
- Smoking cessation: As an adjunct to behavioral therapy
- Nocturnal enuresis: In children over 6 years when other interventions fail
- Chronic urticaria: When antihistamines are insufficient
Nortriptyline is often chosen over tertiary amine TCAs in elderly patients due to its lower anticholinergic burden and reduced orthostatic hypotension risk.
Pharmacokinetics
Nortriptyline is well absorbed from the gastrointestinal tract with bioavailability of 45-70% due to first-pass metabolism. Peak plasma concentrations occur 7-8 hours after oral administration. The drug is highly lipophilic and extensively distributed into tissues, with a large volume of distribution.
Metabolism: Primarily hepatic via CYP2D6, with significant interindividual variability. CYP2D6 poor metabolizers may require lower doses, while ultra-rapid metabolizers may need higher doses or alternative agents. The drug undergoes hydroxylation and conjugation.
Elimination: Half-life ranges from 18-44 hours, allowing once-daily dosing. Steady-state concentrations are achieved in 4-5 days. Metabolites are excreted primarily in urine.
Therapeutic window: Nortriptyline has a well-defined therapeutic window of 50-150 ng/mL. Levels below 50 ng/mL are often ineffective, while levels above 150 ng/mL increase toxicity risk without additional benefit. Therapeutic drug monitoring is recommended to optimize efficacy and minimize adverse effects.
Protein binding is approximately 93-95%, primarily to alpha-1 acid glycoprotein.
Adverse effects
Nortriptyline produces adverse effects through multiple receptor interactions, though it is generally better tolerated than tertiary amine TCAs.
Anticholinergic effects
- Dry mouth, blurred vision, urinary retention
- Constipation, confusion (especially in elderly)
- Precipitation of acute angle-closure glaucoma
- Cognitive impairment and delirium
Cardiovascular effects
- Orthostatic hypotension (alpha-1 blockade)
- Tachycardia and palpitations
- QTc prolongation and risk of torsades de pointes
- Conduction disturbances (prolonged QRS and PR intervals)
- Arrhythmias, particularly in overdose
Central nervous system effects
- Sedation and drowsiness (histamine H1 blockade)
- Lowered seizure threshold
- Tremor and extrapyramidal symptoms
- Withdrawal syndrome if abruptly discontinued
Other effects
- Weight gain and increased appetite
- Sexual dysfunction (decreased libido, erectile dysfunction)
- Sweating and hyperthermia
- Serotonin syndrome when combined with other serotonergic agents
Black box warning: Antidepressants, including nortriptyline, increase the risk of suicidal thinking and behavior in children, adolescents, and young adults (ages 18-24) with major depressive disorder and other psychiatric disorders. Close monitoring is required, especially during the initial months of treatment and after dose changes.
Elderly patients are particularly susceptible to anticholinergic and cardiovascular side effects.
Contraindications and warnings
Absolute contraindications:
- Recent myocardial infarction (within 6 weeks)
- Concurrent use with MAO inhibitors or within 14 days of discontinuing an MAOI
- Acute recovery phase following myocardial infarction
- Known hypersensitivity to nortriptyline or other TCAs
Relative contraindications and warnings:
- Cardiac disease: Use with extreme caution in patients with arrhythmias, heart block, coronary artery disease, or heart failure. Baseline ECG is recommended.
- Seizure disorders: Lowers seizure threshold; use cautiously in epilepsy
- Glaucoma: May precipitate angle-closure glaucoma due to pupillary dilation
- Urinary retention: Prostatic hypertrophy and bladder neck obstruction increase risk
- Hepatic impairment: Dose reduction may be necessary
- Hyperthyroidism: Enhanced sensitivity to catecholamines increases cardiovascular risk
- Bipolar disorder: May precipitate manic episodes; use mood stabilizer concurrently
- Pregnancy: Category D. Use only if potential benefit justifies fetal risk
- Elderly patients: Start at lower doses due to increased sensitivity to anticholinergic and cardiovascular effects
Overdose: TCA overdose is life-threatening. The classic triad includes altered mental status, seizures, and cardiac arrhythmias (wide QRS complex). Treatment includes sodium bicarbonate for QRS widening, benzodiazepines for seizures, and supportive care. Physostigmine is generally avoided due to risk of asystole.
Drug interactions
Nortriptyline has numerous clinically significant drug interactions due to its metabolism and pharmacologic effects.
Serotonergic agents
- MAO inhibitors: Contraindicated. Can cause hypertensive crisis and serotonin syndrome. Minimum 14-day washout required.
- SSRIs, SNRIs, tramadol, linezolid: Increased risk of serotonin syndrome
CYP2D6 interactions
- CYP2D6 inhibitors (fluoxetine, paroxetine, bupropion, quinidine): Increase nortriptyline levels, requiring dose reduction
- CYP2D6 inducers (rifampin, carbamazepine): Decrease nortriptyline levels, potentially reducing efficacy
Cardiovascular drugs
- QTc-prolonging drugs (quinolones, antiarrhythmics, antipsychotics): Additive QTc prolongation and arrhythmia risk
- Clonidine: TCAs may antagonize the antihypertensive effect
- Sympathomimetics: Enhanced pressor response; use with caution
CNS depressants
- Alcohol, benzodiazepines, opioids: Additive sedation and respiratory depression risk
Anticholinergic agents
- Antihistamines, antipsychotics, antiparkinsonian drugs: Additive anticholinergic effects including confusion, ileus, and urinary retention
Other interactions
- Thyroid hormones: May increase cardiac arrhythmia risk
- Cimetidine: Inhibits TCA metabolism, increasing levels
- Warfarin: TCAs may enhance anticoagulant effect; monitor INR
Always review medication lists for potential interactions before initiating nortriptyline.
Clinical pearls
- Therapeutic window monitoring: Nortriptyline is unique among TCAs in having a well-defined therapeutic window (50-150 ng/mL). Measure levels 8-12 hours after the last dose, at steady state.
- Secondary vs tertiary amines: As a secondary amine, nortriptyline causes less sedation, fewer anticholinergic effects, and less orthostatic hypotension than tertiary amines (amitriptyline, imipramine), making it preferable in elderly patients.
- Bedtime dosing: The sedating effect can be therapeutically useful; give at bedtime to improve sleep and minimize daytime drowsiness.
- ECG monitoring: Obtain baseline ECG in patients over 40 years or with cardiac risk factors. Repeat if dose exceeds typical ranges or symptoms develop. A QRS >100 ms or QTc >500 ms warrants dose reduction or discontinuation.
- Gradual titration: Start at a low dose and increase slowly to minimize side effects. Therapeutic effects may take 2-4 weeks to manifest fully.
- Neuropathic pain: Often effective at lower doses than those required for depression, with analgesic effects appearing within 1-2 weeks.
- Discontinuation: Taper gradually over 2-4 weeks to avoid withdrawal symptoms (nausea, headache, malaise, irritability).
- CYP2D6 polymorphism: Consider pharmacogenetic testing in patients with poor response or excessive side effects, as metabolizer status significantly affects drug levels.
- Suicide risk: Monitor closely during the first few months, especially in young adults. Risk may transiently increase as energy improves before mood lifts.
- TCA toxicity mnemonic: The "3 Cs" of TCA overdose are Coma, Convulsions, and Cardiac arrhythmias. Sodium bicarbonate narrows the widened QRS complex by overcoming sodium channel blockade.
TCA side effects — "Tricyclics Can Cause: Sedation, Seizures, Sweating, Suicide risk (young adults); Confusion, Constipation, Cardiac arrhythmias (QRS widening); Anticholinergic effects (dry mouth, blurred vision, urinary retention); Orthostatic hypotension"
Practice questions
1. A 68-year-old man with diabetic neuropathy is started on nortriptyline for pain management. Three weeks later, he presents to the emergency department with confusion, dry mouth, dilated pupils, absent bowel sounds, and urinary retention. His temperature is 38.2°C (100.8°F). Which of the following is the most likely cause of his presentation?
2. A 24-year-old woman with major depressive disorder is brought to the emergency department 2 hours after ingesting 30 tablets of nortriptyline in a suicide attempt. Her blood pressure is 90/60 mmHg, pulse is 120/min, and she is lethargic. ECG shows a QRS duration of 140 ms. Which of the following is the most appropriate next step in management?
3. A 55-year-old man with depression has been taking nortriptyline for 6 weeks with good response. His psychiatrist adds fluoxetine for additional benefit. Two weeks later, he develops tremor, confusion, and excessive sweating. Therapeutic drug monitoring reveals a nortriptyline level of 280 ng/mL. Which of the following best explains this finding?
Frequently asked questions
How does nortriptyline work?
Nortriptyline works by blocking the reuptake of norepinephrine and, to a lesser degree, serotonin at nerve terminals in the brain. This increases the concentration of these neurotransmitters in synapses, which helps regulate mood and reduces pain signaling. As a secondary amine tricyclic antidepressant, it preferentially inhibits norepinephrine reuptake compared to tertiary amine TCAs.
What are the side effects of nortriptyline?
Common side effects include dry mouth, constipation, blurred vision, urinary retention, drowsiness, and dizziness upon standing (orthostatic hypotension). Cardiovascular effects such as rapid heart rate and ECG changes (prolonged QRS and QTc intervals) can occur. Serious risks include cardiac arrhythmias, seizures, and increased suicidal thoughts in young adults. Weight gain and sexual dysfunction are also reported.
Is nortriptyline a controlled substance?
No, nortriptyline is not a controlled substance. It is not classified as a drug with potential for abuse or dependence by the DEA. However, it requires a prescription and should not be stopped abruptly, as discontinuation syndrome (withdrawal symptoms like nausea, headache, and irritability) can occur. Gradual tapering over several weeks is recommended when discontinuing treatment.
Nortriptyline vs amitriptyline — what is the difference?
Nortriptyline is a secondary amine TCA and the active metabolite of amitriptyline, a tertiary amine TCA. Nortriptyline is more selective for norepinephrine reuptake and causes fewer anticholinergic side effects (dry mouth, constipation, confusion) and less sedation than amitriptyline. It also causes less orthostatic hypotension, making it better tolerated, especially in elderly patients. However, both drugs have similar efficacy for depression and neuropathic pain.
What is the therapeutic window for nortriptyline?
Nortriptyline has a narrow therapeutic window of 50-150 ng/mL measured in blood plasma. Levels below 50 ng/mL are often ineffective for treating depression, while levels above 150 ng/mL increase the risk of toxicity without improving efficacy. This makes nortriptyline unique among TCAs in that therapeutic drug monitoring is routinely recommended to optimize dosing and minimize adverse effects.
Conditions it is used for
Related drugs
Sources and further reading
DailyMed (FDA labels)StatPearls (NCBI Bookshelf)MedlinePlusWHO ATC/DDD index: N06AA10
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.