Amitriptyline
Amitriptyline hydrochloride
Also known as: Elavil · Lentizol · Tryptanol · Amitriptylini hydrochloridum · Amitriptylinum · Amitriptyline hydrochloride
Reviewed by the VetSheet Veterinary TeamUpdated Apr 5, 2026Evidence-based veterinary reference
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Dosing by species
🌎 NA — North America🌍 EU — Europe
Dogs
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Adjunctive treatment of pruritus | 1-2 mg/kg PO q12h | PO | q12h | — | 🌎 NA |
| Acral pruritic dermatitis | 2.2 mg/kg PO twice daily | PO | q12h | 2-4 week trial recommended | 🌎 NA |
| Separation anxiety or generalized anxiety | 1-2 mg/kg PO q12h | PO | q12h | — | 🌎 NA |
| Behavior disorders amenable to tricyclics | 1-4 mg/kg PO q12h. Begin at 1-2 mg/kg PO q12h for 2 weeks, increase by 1 mg/kg up to maximum dosage (4 mg/kg) as necessary. If no clinical response, decrease by 1 mg/kg PO q12h for 2 weeks until at initial dosage. | PO | q12h | — | 🌎 NA |
| Behavior disorders amenable to tricyclics | 2.2-4.4 mg/kg PO q12h | PO | q12h | — | 🌎 NA |
| Behavior disorders amenable to tricyclics | 0.25-1.5 mg/kg PO every 12-24h | PO | q12-24h | — | 🌎 NA |
| Neuropathic pain | 1-2 mg/kg PO q12-24h | PO | q12-24h | — | 🌎 NA |
| Adjunctive treatment of pain associated with appendicular osteosarcoma | 1-2 mg/kg PO q12-24h | PO | q12-24h | — | 🌎 NA |
| Management of chronic anxiety, compulsive disorders, and separation anxiety | 1-2 mg/kg | PO | q12-24h | — | 🌍 EU |
- Acral pruritic dermatitis: Only occasionally effective.
- Separation anxiety or generalized anxiety: Use with behavior modification.
- Management of chronic anxiety, compulsive disorders, and separation anxiety: Clomipramine is an authorized preparation for dogs and is claimed to have better anticompulsive properties.
Cats
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Adjunctive treatment of behavior disorders amenable to tricyclics | 5-10 mg per cat PO once daily | PO | q24h | — | 🌎 NA |
| Adjunctive treatment of behavior disorders amenable to tricyclics | 0.5-2 mg/kg PO q12-24h; start at 0.5 mg/kg PO q12h | PO | q12-24h | — | 🌎 NA |
| Adjunctive treatment of behavior disorders amenable to tricyclics | 0.5-1 mg/kg PO q12-24h | PO | q12-24h | — | 🌎 NA |
| Adjunctive treatment of behavior disorders amenable to tricyclics | 0.5-1 mg/kg PO q12-24h. Allow 3-4 weeks for initial trial. | PO | q12-24h | 3-4 weeks initial trial | 🌎 NA |
| Self-mutilation behaviors associated with anxiety | 5-10 mg per cat PO once to twice daily | PO | q12-24h | — | 🌎 NA |
| Self-mutilation behaviors associated with anxiety | 1-2 mg/kg PO q12h | PO | q12h | — | 🌎 NA |
| Pruritus (after other more conventional therapies have failed) | 5-10 mg per cat PO once daily or 2.5-7.5 mg/cat once to twice daily. When discontinuing, taper dose over 1-3 weeks. | PO | q12-24h | — | 🌎 NA |
| Symptomatic therapy of idiopathic feline lower urinary tract disease (FLUTD) | 2.5-12.5 mg (total dose) PO once daily at night | PO | q24h | — | 🌎 NA |
| Symptomatic therapy of idiopathic feline lower urinary tract disease (FLUTD) | 5-10 mg (total dose) PO once daily at night; the drug is in popular use at present and further studies are needed | PO | q24h | — | 🌎 NA |
| Symptomatic therapy of idiopathic feline lower urinary tract disease (FLUTD) | 2.5-12.5 mg (total dose) PO at the time the owner retires for the night. Dosage is adjusted to produce a barely perceptible calming effect on the cat. If no improvement is seen within 2 months, the medication may be gradually tapered and then stopped. | PO | q24h | 2 months trial | 🌎 NA |
| Neuropathic pain | 2.5-12.5 mg/cat PO once daily | PO | q24h | — | 🌎 NA |
| Neuropathic pain | 0.5-2 mg/kg PO once daily; may be a useful addition to NSAIDs for chronic pain. | PO | q24h | — | 🌎 NA |
| Management of psychogenic alopecia, hypervocalization, and idiopathic cystitis | 0.5-1 mg/kg | PO | q24h | — | 🌍 EU |
- Self-mutilation behaviors associated with anxiety: With behavior modification.
- Pruritus (after other more conventional therapies have failed): Taper dose over 1-3 weeks when discontinuing.
- Symptomatic therapy of idiopathic feline lower urinary tract disease (FLUTD): Reserved for cases with severe, recurrent signs.
- Management of psychogenic alopecia, hypervocalization, and idiopathic cystitis: Very bitter taste; can cause ptyalism.
Birds
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Adjunctive treatment of feather plucking | 1-2 mg/kg PO q12-24 hours. Anecdotal reports indicate some usefulness. Barring side-effects, may be worth a more prolonged course of therapy to determine efficacy. | PO | q12-24h | Prolonged course | 🌎 NA |
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Overview
Amitriptyline is a first-generation tricyclic antidepressant (TCA). While newer drugs like clomipramine or SSRIs (e.g., fluoxetine) have largely superseded it for primary behavioral disorders in dogs (such as separation anxiety), amitriptyline remains a highly versatile drug in veterinary medicine.
Clinical Pearl: Its multimodal receptor activity makes it particularly useful for adjunctive treatment of neuropathic pain, pruritus (due to its potent antihistamine effects), and feline idiopathic lower urinary tract disease (FLUTD/FIC). It is also occasionally used in avian medicine to manage feather-plucking behaviors.
Mechanism of action
Amitriptyline and its active metabolite, nortriptyline, exhibit a complex pharmacologic profile, affecting multiple receptor systems:
- Serotonin (SERT) & Norepinephrine (NET) Reuptake Inhibition: Blocks the amine pump → increases synaptic levels of 5-HT and NE → mood stabilization and descending pain pathway modulation.
- H1-Receptor Antagonism: Potent antihistamine effect → stabilizes mast cells and provides antipruritic action.
- M1-Muscarinic (Anticholinergic) Antagonism: Causes smooth muscle relaxation (useful in FLUTD) but also leads to side effects like dry mouth and urine retention.
- Alpha-1 Adrenergic Antagonism: Can cause mild vasodilation and sedation.
- NMDA Receptor & Sodium Channel Blockade: Contributes to its efficacy in treating chronic, neuropathic pain.
Safety & warnings
Contraindications
- Prior sensitivity to any tricyclic antidepressant
- Concomitant use with monoamine oxidase inhibitors (MAOIs)
Adverse effects
- Sedation
- Constipation
- Urinary retention
- Hyperexcitability (dogs)
- Seizures (rare)
- Cardiac dysrhythmias
- Bone marrow suppression
- Vomiting
- Diarrhea
- Hypersalivation (cats)
- Anorexia (cats)
- Thrombocytopenia
- Neutropenia
- Unkempt hair coat (cats)
- Ataxia
- Disorientation
Precautions
Use with extreme caution in patients with seizure disorders as tricyclic agents may reduce seizure thresholds. Use with caution in patients with thyroid disorders, hepatic disorders, keratoconjunctivitis sicca (KCS), glaucoma, cardiac rhythm disorders, diabetes, or adrenal tumors. FDA Pregnancy Category D (restrict use to pregnant animals only when benefits clearly outweigh risks).
Drug interactions
Increased effects; hyperthermia and ileus possible
May inhibit tricyclic antidepressant metabolism and increase the risk of toxicity
May have additive effects on QTc interval; possible serious arrhythmias may result
Potential life-threatening serotonin syndrome; use together not recommended
Increased sedative effects
Possible increased amitriptyline levels
Increased risk for QTc interval prolongation and tricyclic adverse effects
Potential increased amitriptyline levels, increased risk for serotonin syndrome; enhanced monitoring suggested if used together
May increase the risk of cardiac effects (arrhythmias, hypertension, hyperpyrexia)
Increased risk for arrhythmias; monitor closely
Risk of fatal serotonin syndrome. Requires a minimum 2-week washout period.
Metabolized by CYP2D6; may alter amitriptyline metabolism.
Concurrent use increases the risk of serotonin syndrome.
Concurrent use increases the risk of serotonin syndrome.
Increased risk of serotonin syndrome and seizure threshold reduction.
Monitoring
- Clinical efficacy (behavior, pain, or pruritus improvement)
- Adverse effects
- Baseline cardiac evaluation (ECG) prior to therapy
- Baseline CBC and serum chemistry panel prior to therapy
- Liver enzymes in cats (prior to therapy, 1 month after initial therapy, and yearly thereafter)
Pharmacokinetics
Half-life
Absorption
Rapidly absorbed from both the GI tract and parenteral injection sites. Transdermal (PLO-gel based) absorption in cats is poor. Peak levels occur in 1-2 hours after oral administration in cats and within 2-12 hours in other species.
Distribution
Highly bound to plasma proteins. Enters the CNS and enters maternal milk in levels at or greater than those found in maternal serum.
Metabolism
Metabolized in the liver to several metabolites, including the active metabolite nortriptyline.
Elimination
Eliminated primarily via hepatic metabolism.
Overdose
Overdosage with tricyclics can be life-threatening (arrhythmias, cardiorespiratory collapse). Because toxicities and therapies are complicated, it is recommended to contact an animal poison control center immediately in any potential overdose situation.
- Dogs: Common findings include lethargy and tachycardia.
- Cats: Common findings include vocalization, ataxia, mydriasis (dilated pupils), tachycardia, disorientation, lethargy, and agitation.
Available products
Formulations
- Tablets
- Injection
Human-labeled
- Amitriptyline HCl Tablets: 10 mg, 25 mg, 50 mg, 75 mg, 100 mg, & 150 mg
Regulatory status
POM (Prescription Only Medicine). Clomipramine is the authorized TCA for dogs in the EU.
POM-V. Prescribed under the cascade as human generic preparations.
No regulatory data for: 🇺🇸 US · 🇭🇰 HK · 🇹🇼 TW · 🇯🇵 JP · 🇰🇷 KR · 🇦🇺 AU
Storage & stability
Tablets should be stored at room temperature. The injection should be kept from freezing and protected from light.
Client information
Patience is Key: Behavioral changes will not happen overnight. It typically takes several weeks of consistent daily dosing to see the full effect.
- Do not stop abruptly: If discontinuing the medication, the dose must be tapered slowly under veterinary guidance to prevent withdrawal signs.
- Side Effects: Your pet may seem sleepy or have a dry mouth (you might notice increased lip smacking). Constipation or difficulty urinating can occur; notify your vet if you see these signs.
- Toxicity Warning: Keep strictly out of reach of children and other pets in child-resistant packaging. An overdose can be fatal.
- Administration: The pills can be bitter. Hiding them in a highly palatable treat or pill pocket is recommended.
VetSheet drug reference is intended for licensed veterinary professionals as a clinical decision-support aid, not a substitute for professional judgement or the manufacturer’s current label.