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The way mirtazapine works in the brain is complicated. It's called a serotonin agonist-antagonist. This means it acts like serotonin one way and blocks serotonin another way. It also blocks histamine (like Benadryl), which is part of why it makes humans sleepy. It may work in even more ways that aren't understood yet.3 4
Can Dogs Take Mirtazapine?
Your veterinarian may prescribe mirtazapine for your dog if other drugs don't work -- this is because it isn't a preferred first choice. Other drugs usually work better. Unlike humans, who use it for depression and to help them sleep, dogs use mirtazapine to help with vomiting and poor appetite.
If your dog is vomiting or needs help gaining weight and you and your vet have tried other drugs that aren't working, bring up mirtazapine with them and discuss it!
What is Mirtazapine Used for in Dogs?
Mirtazapine makes dogs hungrier and helps block their vomit response. If your dog get sick with cancer, liver disease, or kidney disease and isn't eating, mirtazapine can help stimulate their appetite and help them keep food down.3 5
What Dogs Should NOT Take Mirtazapine?
Dogs with severe kidney or liver disease may need special dosing for mirtazapine. They won't be able to clear the drug from their system as quickly. 5 If you know your dog has liver or kidney disease, or a history of liver or kidney disease, make sure your veterinarian knows and has determined whether or not your dog needs a dose adjustment.
How Does Mirtazapine Work? How Long Will it Take to Work?
The way mirtazapine works is not fully understood. It both acts like serotonin in certain areas the brain and blocks serotonin in other areas of the brain. It blocks histamine like Benadryl does. Lastly, it blocks alpha receptors, although it's not well-understood if this helps it work.3 4 5
Mirtazapine will start to work in 3-4 hours after the first dose. 3
Is Mirtazapine Safe in Dogs? Are There Drug Interactions?
Yes! As long as your dog's liver and kidneys are healthy, mirtazapine is not known to be dangerous. There are a few types of drugs that can interact with mirtazapine. Antidepressants called selective serotonin reuptake inhibitors (SSRIs), serotonin-norepinephrine reuptake inhibitors (SNRIs), and monoamine oxidase inhibitors (MAOIs) can be problems.
Examples include fluoxetine (Prozac), duloxetine (Cymbalta), and selegiline (Eldepryl).3 Talk to your veterinarian if your dog is on these or any other drugs for anxiety, depression, or cognitive decline as part of discussing mirtazapine.
What Should I Expect If My Dog Is On Mirtazapine? Are There Side Effects?
You should look for your dog's appetite to improve, and for them to vomit less often starting within hours of the first dose. Your pup should want food more and eat more, gaining weight over the next few weeks of use.
Side effects are rare in dogs. Mirtazapine is usually well-tolerated.3
Benefits/Risks Sections
- Benefits
- Few/no side effects.
- Once-daily dosing in dogs.
- Inexpensive.
- Risks
- May not be effective.
What Forms Does Mirtazapine Come In?
Mirtazapine is available as6:
-
7.5mg tablets
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15mg tablets
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30mg tablets
-
45mg tablets
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15mg dissolving tablets
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30mg dissolving tablets
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45mg dissolving tablets
How to Safely Store Mirtazapine?
You should keep mirtazapine tablets should be stored at room temperature, protected from light and moisture. 7
Mirtazapine dissolving tablets should be kept the same way. Additionally, you need to store the dissolving tablets in their original sealed blister package. Once the tablet is removed, it should be used immediately or discarded. Once they're exposed to air, the moisture in the air will cause the tablet to break down and the drug inside to lose potency. It won't work well.8
Mirtazapine Dosage in Dogs
Mirtazapine is dosed at 0.5-1mg/kg once daily in dogs.3
Mirtazapine Dose Table
| Dog Weight in lbs | 0.5mg/kg dose | 1mg/kg dose |
|---|---|---|
| 5lbs | 1mg | 2mg |
| 10lbs | 2mg | 4mg |
| 15lbs | 3mg | 6mg |
| 20lbs | 5mg | 10mg |
| 25lbs | 6mg | 12mg |
| 30lbs | 7mg | 14mg |
| 35lbs | 8mg | 16mg |
| 40lbs | 9mg | 18mg |
| 45lbs | 10mg | 20mg |
| 50lbs | 11mg | 22mg |
What If I Miss Giving a Mirtazapine Dose?
If you miss giving your dog their daily mirtazapine dose and you remember on the same day, give the dose when you remember. If you forget until the next day, do not double the dose. Give the next dose.
Alternatives to Mirtazapine
- Maropitant(Cerenia): Maropitant is an anti-vomiting drug used much more commonly in dogs than mirtazapine.3 It is more effective, but also more expensive. 9
- Meclizine(Antivert, Bonine): Meclizine is a human anti-vomiting drug sometimes used in dogs. While inexpensive, it is not as good a choice as maropritant for anti-vomiting most of the time. It may be useful for dogs with motion sickness.3
- Ondansetron(Zofran): Ondansetron is good for blocking vomiting and nausea in humans, but dogs barely absorb it through their gut. Don't use ondansetron for your dog! 3
- Capromorelin(Entyce): Capromorelin is effective for making dogs hungrier. It mimics a hormone your dog's gut makes to make them want to eat.3
Natural Alternatives/Supporting Therapies to Mirtazapine
There is not much evidence for the use of natural substances or herbs to directly increase a dog's appetite.
Instead, try to find the underlying reason why your dog isn't wanting to eat (infection, pain, anxious, etc) and treat that. Then their appetite will improve.
If you know your dog has chronic pain or anxiety, then there are natural options.
-
CBD: Cannabidiol or CBD is an excellent choice to relieve pain or anxiety in dogs. It has been shown to relieve pain and pain-related anxiety in dogs. Many owners report that starting CBD helps their dogs eat better if the pain or anxiety was leading to poor diet.
See our page on CBD for more information!
Cost
Mirtazapine costs from $9-$20 for 30 tablets, or one month supply. 10
Conclusion
It can be heartbreaking to watch a beloved pet and family member waste away due to lack of appetite. The best approach is always to try and find the reason a pet isn't eating - and CBD may be a help if pain or anxiety are preventing your pet from wanting a healthy meal.
If your pet needs direct help with appetite, mirtazapine is a reasonable choice after first choices like Entyce have failed, or your pet needs both help suppressing vomiting and wanting to eat more.
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