Naltrexone
Naltrexone hydrochloride
Also known as: ReVia Β· Vivitrol Β· EN-1639A Β· Naltrexone HCl
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
π NA β North Americaπ EU β Europe
Dogs
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| As adjunctive therapy in behavior disorders (tail chasing or excessive licking) | 1-2 mg/kg | PO | daily | Long-term therapy may be required | π NA |
| As adjunctive therapy in behavior disorders | 2-5 mg/kg | PO | once daily | β | π NA |
| As adjunctive therapy in behavior disorders | 1-2.2 mg/kg | PO | q8-12h | β | π NA |
| For the adjunctive treatment of acral pruritic dermatitis | 2.2 mg/kg | PO | once daily | one-month trial | π NA |
- As adjunctive therapy in behavior disorders (tail chasing or excessive licking): First give 0.01 mg/kg SC of naloxone to determine if narcotic antagonists may be effective, if so give naltrexone.
- For the adjunctive treatment of acral pruritic dermatitis: Some dogs exhibit drowsiness and minor changes in behavior. 50-60% of patients have benefited. Expense is of concern.
Cats
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| As adjunctive therapy in behavior disorders | 25-50 mg/cat | PO | q24h | β | π NA |
- As adjunctive therapy in behavior disorders: Note: has a bitter taste
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Overview
Naltrexone is a synthetic, long-acting pure opioid antagonist. While structurally similar to naloxone, it has significantly higher oral bioavailability and a longer duration of action.
In veterinary medicine, it is primarily utilized off-label as an adjunctive treatment for compulsive behavior disorders, such as:
- Acral lick dermatitis (lick granulomas)
- Tail chasing
- Flank sucking
- Other self-mutilating or stereotypic behaviors
Clinical Pearl: The rationale for its use in behavior medicine stems from the hypothesis that stereotypic behaviors stimulate the release of endogenous opioids (endorphins), which reinforce the behavior. By blocking these receptors, naltrexone removes the internal "reward," helping to extinguish the compulsive action.
Mechanism of action
Naltrexone acts as a competitive antagonist at opioid receptors, with the highest affinity for βΞΌ (mu)β receptors, followed by βΞΊ (kappa)β and βΞ΄ (delta)β receptors.
- Mechanism in Behavior Disorders: Compulsive behaviors β Release of endogenous endorphins β Binding to ΞΌ-receptors β Reinforcement/Analgesia.
- Naltrexone blocks these receptors β Prevents endorphin binding β Eliminates the auto-reinforcing reward loop of the stereotypic behavior.
Safety & warnings
Adverse effects
- Drowsiness
- Minor changes in behavior
- Elevated hepatic enzymes (AST, ALT)
Precautions
Naltrexone may cause increases in hepatic function tests (e.g., AST, ALT). It can interfere with some enzymatic assays (though it does not interfere with TLC, GLC, or HPLC methods for urinary opiates). The drug has a bitter taste, which may complicate oral administration, particularly in cats.
Drug interactions
May antagonize the effects of these agents, including respiratory depression and analgesia.
Naltrexone may reduce the hypotensive and bradycardic effects of clonidine.
Naltrexone may increase the CNS effects of yohimbine (anxiety, tremors, nausea, palpitations) and increase plasma cortisol levels.
Monitoring
- Clinical efficacy (reduction in stereotypic behaviors)
- Liver enzymes (AST, ALT) if using very high doses with prolonged therapy
Overdose
Specific overdosage information is not provided in the monograph. However, as an opioid antagonist, massive overdoses could theoretically cause dysphoria or precipitate withdrawal in opioid-dependent patients. Monitor liver enzymes if very high doses are ingested.
Available products
Formulations
- Oral tablets
- Powder for suspension extended-release injection
Human-labeled
- Naltrexone HCl Oral Tablets: 50 mg; ReVia (Duramed); generic
- Naltrexone HCl Powder for Suspension Extended-Release Injection: 380 mg/vial in single-use vials w/4 mL diluent; Vivitrol (Alkermes)
Regulatory status
No regulatory data for: πΊπΈ US Β· πͺπΊ EU Β· π¬π§ UK Β· ππ° HK Β· πΉπΌ TW Β· π―π΅ JP Β· π°π· KR Β· π¦πΊ AU
Storage & stability
Naltrexone tablets should be stored at room temperature in well-closed containers.
Client information
Medication Compliance is Key: It is crucial to follow the exact dosing schedule prescribed by your veterinarian for this medication to be effective.
- Comprehensive Approach: Medication alone is rarely a cure. Additional behavior modification techniques and environmental enrichment are usually required to successfully alleviate your pet's symptoms.
- Administration: This medication has a very bitter taste, which can make giving it to cats particularly challenging. Consider hiding it in a highly palatable treat or placing it inside an empty gelatin capsule.
- What to Watch For: Some pets may experience mild drowsiness or subtle changes in behavior. Contact your veterinarian if these effects are severe or concerning.
VetSheet drug reference is intended for licensed veterinary professionals as a clinical decision-support aid, not a substitute for professional judgement or the manufacturerβs current label.