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Tetracyclic Antidepressant; 5-HT3 Antagonist

Prescriber Highlights

Used primarily as an appetite stimulant and antiemetic in dogs and catsPrimary side effect is sedationIn cats, vocalization and increased affection can be notedUse lowest effective dose to reduce sedative propertiesDo not exceed 30 mg q24h when using for appetite stimulation in dogsCan be used in conjunction with other antiemetics

Uses, Indications

  • Used mainly as an appetite stimulant and antiemetic in patients with chronic kidney disease
  • Higher doses (3.75 mg per cat) are associated with significantly more noticeable behavioral changes
  • Can potentially be used to treat chemotherapy-induced nausea and vomiting, behavior-related conditions, congestive heart failure, GI disorders, liver disease, or neoplasia 

Contraindications, Precautions, Warnings

  • Contraindications

Patients hypersensitive to mirtazapine; patients that have received monoamine oxidase inhibitors within 14 days

  • Precautions

Has been associated with orthostatic hypotension in people and should be used with caution in patients with known cardiac disease or cerebrovascular disease that could be exacerbated by hypotension

  • Warnings

Abrupt discontinuation after long-term administration has resulted in withdrawal symptoms (eg, nausea, headaches, malaise) in humans

Side Effects

  • Drowsiness, sedation
  • Vocalization and increased affection in cats
  • Hypotension
  • Tachycardia
  • Increase in liver enzymes has been reported in cats

Drug Interactions

  • Cyproheptadine may negate the effects of mirtazapine
  • Tramadol, selegiline, linezolid, and amitraz may increase the risk for serotonin syndrome

Client Information

  • Tolerated well in dogs
  • Most side effects are noted in cats


  • Clinical efficacy is measured by increased appetite, decreased vomiting episodes, and weight gain
  • Liver enzymes in cats
  • Adverse effects on behavior

Dosage Forms

  • Mirtazapine oral tablets: 7.5, 15, 30, and 45 mg

Compiled and summarized from Plumb’s Veterinary Drugs by Shannon Palermo, VMD

Information about this drug was adapted from Plumb’s Veterinary Drugs. Further details and more therapeutics can be found with a subscription at

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