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Mirtazapine is a tetracyclic antidepressant when used to treat humans. However, it has an appetite-inducing effect on animals. It is hence prescribed by veterinarians to treat conditions ranging from behavioral problems to anorexia (loss of appetite) in cats.

Mirtazapine also has anti-nausea effects since it acts on the neuroreceptors in the intestine and stomach. Though Mirtazapine increases serotonin in the central nervous system, it counteracts serotonin in the gastrointestinal tract.

How Is It Administered?

Mirtazapine can be found in different strengths of oral and topic formulations. The dosage, formulation and the frequency of administration are decided according to the condition the drug is being used to treat and the type and size of the animal receiving the drug.

There is also a transdermal gel formulation of this drug that has been developed for cats. It is applied to the skin of their inner ears once a day. The layer of medicine should not be disturbed to allow better absorption and the ear on which the gel is applied should be alternated daily.


Mirtazapine should never be prescribed to an animal who is hypersensitive or allergic to the drug as the chances of an adverse allergic reaction are very high. Caution must be exercised whenever the animal is taking some other medicine as those might interact Mirtazapine in an undesired way. This holds especially true for drugs like tramadol and MAO inhibitors.

The effects of Mirtazapine are also unknown during pregnancy and lactation and it is best to not administer the drug to a pregnant feline. Also, a reduced dose is recommended for patients who suffer from any kind of renal or liver diseases.

Patients who receive this drug should be weaned off of it slowly rather than ceasing the administration of the drug immediately.

Mirtazapine Dosage For Cats

Mirtazapine Dosage For Cats

Mirtazapine in tablet form is given to cats every 2-3 days. The ideal initial dosage for cats is considered to be 1.8mg though it was thought to be 3.75mg in the beginning. The most commonly found dosage, however, is 15mg, though these pills need to be cut and divided into the exact prescribed dosage. It is crucial that whoever administers the dose does it accurately.

When administered as a gel, Mirtazapine should be applied once daily to the skin of the cat’s inner ear. The one applying the gel must wear gloves and should dispose of them immediately after applying it. The applied layer should not be disturbed in any way whatsoever in order to aid proper absorption.

It has been observed that adverse effects are caused most frequently by the 15mg dosage. However, such effects may be caused by other dosages as well.

Mirtazapine For Cats Side Effects

Though there aren’t many drug trials relating to the side effects of Mirtazapine, it is usually well tolerated by dogs and cats. Since Mirtazapine is an antidepressant, it raises the amount of serotonin in an animal’s body, hence, hyperactivity was reported in 11% of cats that received the drug in the form of the transdermal gel.

They also tend to show more affectionate behaviour and also increased vocalization. The side effects of Mirtazapine may also manifest in the form of drowsiness.

Mirtazapine’s effect as a serotonin enhancer may also cause elevated heart rate, breathing difficulties, high body temperatures, hypertension, and tremors. These symptoms all point towards serotonin syndrome. Mirtazapine also decreases the secretion of cortisol by the adrenal gland.

Though it is not prescribed to animals that are allergic to it, a higher dose may still cause an allergic reaction, even in animals that are not allergic to Mirtazapine. Such a reaction may manifest in breathing difficulties, spouting of hives, swollen lips, face or tongue.

Though seldom, Mirtazapine has been the cause of abnormalities in a patient’s marrow development.  If a patient suffers from leukaemia or any other blood diseases, Mirtazapine can still be used, however extreme caution must be exercised, and the patient must be tested and monitored heavily. Use of Mirtazapine may also cause elevated liver enzymes; however, this effect should subside within a month of withdrawal.

Appetite Stimulant For Cats

Mirtazapine Vs Cyproheptadine

Cyproheptadine is an antihistamine, yet it is hardly ever used for its antihistamine effects. The appetite-stimulating effect of Cyproheptadine is the main reason why it is prescribed though it can also be used as an anti-inflammatory drug. Cyproheptadine is usually administered to patients twice in a day. Its side effects are caused by its antihistamine effects, the most common of those being drowsiness. However, cats may have an opposite reaction and may enter a state of excitement.

Other side effects include urine retention, increase pressure in the eye, dry mouth, elevated heart rate and body temperature. Cyproheptadine also magnifies the sedation effects of other sedatives. It should never be prescribed to nursing or pregnant felines as it may affect lactation and milk production.

Cyproheptadine is known to interfere with serotonin reuptake inhibitors which are usually prescribed for anxiety. Sertraline, fluoxetine and paroxetine are some of the serotonin reuptake inhibitors with which Cyproheptadine may interact.

Cyproheptadine can also be used to treat serotonin syndrome which is caused by the excessive use of Mirtazapine as it raises the levels of serotonin in the brain.

Tremors, dilated pupils, breathing difficulties and an elevated heart rate caused by serotonin syndrome can be cured through the use of Cyproheptadine. It reduces the brain serotonin levels and can be used to reverse serotonin syndrome.

Cyproheptadine Vs Mirtazapine For Cats


For cats, Mirtzapine works very effectively as an appetite stimulant. It is a very effective tool for dealing with a cat’s finicky appetite. It should however only be administered upon a veterinarian’s advice and prescription.

Though it has a few side effects such as breathing difficulties, drowsiness, elevated heart rate, and serotonin syndrome, they are easily mitigated through the use of counteractive drugs such as Cyproheptadine.

Mirtazapine is also effective in treating anxiety in felines, making it a boon for pharmacologists around the world. It is safe to say that Mirtazapine is a relatively safe and highly effective drug that can be used to treat a whole host of diseases that plague felines around the world.


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