Vitamin B12 for Cats: Overview, Dosage & Side Effects

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Vitamin B12, also called cyanocobalamin, is a water soluble vitamin that is often supplemented in cats with certain health conditions, especially of the GI tract. In this article, you’ll learn why B12 is important, situations when a vitamin B12 supplement is needed, and some frequently asked questions.

Vitamin B12 for Cats Overview

Medication Type:
Chewable tablets, injectible solution
Prescription Required?:
Only for the injectable.
FDA Approved?:
Life Stage:
All life stages
Brand Names:
Cobalequin (chewable tablets)
Common Names:
Cyanocobalamin, Vitamin B12
Available Dosages:
Chewable tablets in 250 mcg, and 1000 mcg; Injection in 1000, 3000, and 5000 mcg/ml in 100ml, 250ml, and 500ml size.
Expiration Range:
Vitamin B12 should be stored below 104 degrees F (40 degrees C) but prevented from freezing and protected from light.

About Vitamin B12 for Cats

Vitamin B12, or cyanocobalamin or just cobalamin (going forward, we’ll use all three terms interchangeably), is required for many enzymatic processes in animals that are needed for normal cell growth and function, including protein synthesis, nerve conduction, metabolism of fats and carbs, and generation of new red blood cells.

In a natural sense, B12 can only be obtained from a diet that includes meat, eggs, and poultry. As obligate carnivores, cats require certain nutrients from muscle tissue protein, including B12 and taurine.

For cats, obtaining B12 adequately from their diet is generally not a problem. In humans, B12 deficiencies are seen more commonly in people consuming a vegetarian or vegan diet who are not supplementing enough B12.

Deficiencies in B12 can cause a host of abnormal signs. According to Harvard Medical School, people with cobalamin deficiency may experience subtle but unusual and progressive signs of illness, including strange tingling or numb sensations, difficulty walking, cognitive and memory issues, and weakness.

In cats, we often find that issues of the digestive system go hand in hand with B12 deficiencies. This is because like all other cells, intestinal cells require B12 for regeneration and health.

Also Read: The 7 Best Cat Vitamins And Supplements

What Does Vitamin B12 Do for Cats?

Cats with gastrointestinal disease might suffer from vitamin B12 deficiency.

In cats, vitamin B12 deficiency is seen most often with an inflammatory disease of the bowel. This may be true inflammatory bowel disease (IBD) or may also be gastrointestinal low grade lymphoma. In these conditions, bowel thickening and inflammation leads to poor absorption of nutrients and weight loss.

B12 is poorly absorbed in these conditions, like other nutrients, but its deficiency from poor absorption also contributes to further negative changes in intestinal health.

According to an article about cobalamin deficiency in Tufts University’s catnip newsletter, people with cobalamin deficiency also experience changes with intestinal permeability and absorptive function.

Studies have shown that supplementing cobalamin in deficient cats experiencing gastrointestinal disease, like vomiting and diarrhea, has led to a significant improvement in GI signs, as well as weight gain.

It remains a phenomenon as well, that even if you treat a cat for a disease like IBD with steroids or immunosuppressant medication and a prescription diet, their response will never be as full or complete unless B12 supplementation is also included.

Also Read: 10 Subtle Signs Your Cat May Be Sick

Side Effects of Vitamin B12 for Cats

Fortunately, vitamin B12 is extremely safe. As a water-soluble vitamin, any excesses the body does not need are simply excreted in the urine. This is unlike fat soluble vitamins, like vitamins A, D E, and K, which will continue to get stored in the body’s fat when supplemented excessively, and can lead to side effects if over supplemented beyond the body’s needs.

Though uncommon, vitamin B12 may sting a little on injection, though this is usually a short-lived side effect. This is also more common for hydroxocobalamin, a form that is used less commonly in veterinary medicine.

Also Read: Top 10 Things Your Vet Wishes You Knew

Vitamin B12 for Cats Dosage

Cats with inflammatory bowel disease initially receive an injection of vitamin B12 once a week for six weeks.

Dosage recommendations differ depending on whether an injectable or oral form of vitamin B12 is being used.

In cats, it is most common for B12 to be supplemented by a subcutaneous injection under the skin. For cats with inflammatory bowel disease, the most common recommended schedule for B12 injections is to give 250 micrograms per cat once a week for six weeks.

Most cyanocobalamin is provided at a 1000 microgram/milliliter concentration, so this often equates to 0.25ml. However, it does come in higher concentrations, so always be aware of what you have if giving at home.

After the initial six weeks, the injections can be tapered down to being given less frequently, often once every one to two months. This is because though cobalamin will take a couple of weeks to reach appropriate levels in the body, especially if deficient, it can last in the body for a long time once it reaches appropriate concentrations.

The injections given under the skin may be performed as a service at your veterinary practice. Pet owners might also be comfortable giving the injections at home, after a brief demo by a veterinary professional.

If you do the injections at home, it can be best to do them while your cat is calm or distracted, such as during a meal. Because the injections are given infrequently with a very small needle (typically a 25-gauge needle is adequate), this is not usually a very unpleasant experience for the cat.

If doing injections at home, always remember to properly dispose of any needles and syringes in a sharps container or well-sealed heavy plastic container. Check with your veterinarian for the best methods of disposing containers containing sharps in your area.

Also Read: How To Give Subcutaneous Fluids To A Cat

Vitamin B12 also comes in oral forms. Cobalequin made by Nutramax is a cyanocobalamin chewable tablet supplement formulated for dogs and cats, that comes in a 250 microgram size. Oral supplementation of B12, unlike the injection, must be given every day. The initial loading period for the oral form is also longer, lasting 12 weeks.

Cobalamin blood levels can be monitored, and many veterinarians prefer to check these levels at the time of diagnosis for GI disease, as well as periodically during treatment, to determine if B12 levels are remaining normal. This is especially the case after the loading period is finished, to help determine the right frequency thereafter.

A majority of cats that require B12 supplementation, especially for GI disease, will require therapy for life.

Also Read: How To Give Your Cat A Pill (With 7 Proven Tips!)

In Summary

Vitamin B12 (cyanocobalamin or cobalamin) is a crucial vitamin for many of the body’s everyday processes, and deficiencies can contribute to serious disease. In cats, deficiencies are often linked to gastrointestinal disease, especially inflammatory bowel disease and lymphoma.

B12 supplementation is very safe and side effects are very rare, but supplementation is often required for life.

Drug Dosing Disclaimer: We are only able to provide doses for medications that are FDA approved for use in cats and only as the label guidelines dictate. For medications that are used off-label we can only provide guidelines and safety information for use. Safe and appropriate dosing for off-label medications can only be determined by a primary care veterinarian.

We encourage you to work with your veterinarian to determine if a particular medication is appropriate for your cat. Changing or adjusting a dose for your cat on your own without consulting with a veterinarian can carry risk. We do not encourage use of medications prescribed for human use in pets without first consulting with a primary care veterinarian.

Frequently Asked Questions

Can I give my cat vitamin B12?

Yes, supplementing vitamin B12 is generally very safe and beneficial especially in cases with gastrointestinal disease coupled with weight loss. 

It is important however, to know what disease process may be contributing to a B12 deficiency and to follow the correct dosing protocol for oral or injectable B12 supplementation. If not loaded correctly, B12 supplementation may not be sufficient. 

How often should I give my cat B12?

For injections given under the skin, the most common protocol is to give 250 micrograms once a week for an initial six weeks. After that initial period, it is common to continue injections monthly, though less frequent intervals might be OK if cobalamin blood levels are supportive. 

 For oral B12 supplementation with a supplement like Cobalequin, 250 micrograms must be given once daily and continued initially for 12 weeks. Daily supplementation may need to be continued, but cobalamin blood levels could be monitored with less frequent dosing to see if decreased frequency of administration is adequate. 

How long does vitamin B12 take to work in cats?

Vitamin B12 does require the initial loading dose period, especially in very deficient cats, so improvements will not be immediate. 

Generally, you will start to see improvements within two weeks, usually in terms of vomiting and/or diarrhea frequency. If your cat has lost a lot of weight due to GI disease, it may take several weeks to see a visible difference.

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About Dr. Chris Vanderhoof, DVM, MPH

Dr. Chris Vanderhoof is a 2013 graduate of the Virginia-Maryland College of Veterinary Medicine (VMCVM) at Virginia Tech, where he also earned a Masters in Public Health. He completed a rotating internship with Red Bank Veterinary Hospital in New Jersey and now works as a general practitioner in the Washington D.C. area. Dr. Vanderhoof is also a copywriter specializing in the animal health field and founder of Paramount Animal Health Writing Solutions, which can be found at Dr. Vanderhoof lives in the Northern Virginia area with his family, including 3 cats.

12 thoughts on “Vitamin B12 for Cats: Overview, Dosage & Side Effects”

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  1. ann mckinley

    my cat has thyroid and kidney conditions and has recently put on b12 protexin cobalaptex caps every other day. is there a way to change her diet to cover all these conditions?

    1. Avatar photoDr. Chris Vanderhoof, DVM, MPH Post author

      Hi Ann,

      I can assume you’re referring to hyperthyroidism and chronic kidney disease specifically, as these are common conditions in cats, especially to be seen together. The one prescription diet that could cover both conditions is Hill’s y/d, which is formulated with limited iodine content as a way of treating hyperthyroidism from a nutritional approach.

      The diet is also formulated with restricted phosphorus, which is an important part of nutritionally supporting cats with kidney disease.

      The downside to feeding y/d as a way of treating hyperthyroidism, is that no other food items can be fed or this will interfere with the iodine restriction principle. This plus the pickiness of many cats and that the methimazole medication used to treat hyperthyroidism is pretty inexpensive has made it a less common choice.

      However, the upside is that y/d may be a better option for cats adverse to medication administration or for cats with a sensitivity to methimazole.

      B12 supplementation certainly doesn’t hurt.

  2. Linda Van Dover

    My 16 yr old cat has stage one kidney disease and just had a complete blood test and her RBC shows she is anemia.
    I ordered B-12 liquid because she is so hard to pill. My question is could i give this directly into her mouth or does it have to go into her water or food which is dry food….she refuses to eat wet!!

    1. Avatar photoDr. Chris Vanderhoof, DVM, MPH Post author

      Hi Linda,

      As far as how to use the product you have, I can’t tell you for certain as there are many different ones available. If it’s an oral product for cats that you purchased, there should be recommended amounts somewhere on the packaging.

      One that I found suggested it could be added to either food or water but that giving with food may provide better absorption by the body.

      You could also consider B12 injections too, either at your vet or you could learn how to do them at home.

      A note about anemia and kidney disease. While B12 deficiency can cause anemia, supplementing B12 if it’s not the cause will not correct an anemia. It is possible to test for B12 levels through a test offered by Texas A & M. If supplementing may be stressful for you and your cat, it may be worth testing to see if the levels are even low.

      A mild anemia of chronic disease is common with many conditions and usually has no effect on the cat. Kidney disease can cause anemia as well but we usually see it more of a concern with later stages of kidney disease that have progressed over time.

      In most cases, internists will not treat an anemia unless the red cell count drops below 25%. This is because slow progressive anemias often cause no significant changes in a pet unless they get very severe.

    2. Cathy Derry

      My cat is 14 years old and has IBS. She has diarrhea and just put on B12 injections. She does not always use the litter box and this is frustrating. How long will it take to get tge diarrhea under control?

    3. Avatar photoDr. Chris Vanderhoof, DVM, MPH Post author

      Hi Cathy,
      It can be different in every cat and can also depend on the degree of disease and severity, as well as how effective other parts of the treatment are too (I assume your kitty may also be on a steroid medication and/or a prescription diet). The B12 injection protocol per Texas A & M is 6 weeks of the weekly injections, then a 7th one month later before retesting B12 levels. I try to set the expectation that it could take that long, but hopefully we see improvement much sooner, within the first month of treatment. As far as the B12 injections goes, improvement may depend on how much of a B12 deficiency is because of the IBD vs. how much of the diarrhea is caused by the B12 deficiency. It can be a chicken vs. egg kind of thing. We do know at least that a good majority of cats with IBD are B12 deficient and that supplementing does help to improve their signs of illness more quickly.

  3. Linda Van Dover

    Thank you for your response, not sure if her rbc is below 25% her results show 6.96 normal is 7.12-11.46
    I have been giving her B-12 liquid orally due to her only eating dry food & refuses wet food.
    Is B-12 and B-complex essential to give a kidney stage 1 cat? On the bottle it says to give .5ml to cats & for chronic illness 1ml.
    So by giving both it can’t hurt only help i’m I correct or not?

    1. Avatar photoDr. Chris Vanderhoof, DVM, MPH Post author

      Hi Linda,

      The numbers you reference sound more like hemoglobin values, not your red cell concentration (hematocrit or HCT). Many bloodwork parameters will have the HCT range somewhere around 35%-50%. We don’t get too worried with a mild drop, maybe in the low thirties, as long as we’re looking at small changes over long periods. This is more often what we see progressively with kidney disease.

      I would not say that B 12 or B complex vitamins are essential for a Stage I CKD cat. In most cases, these cats are still eating normally and not experiencing nutritional deficiencies. B vitamin supplementation may be seen more in later stages of kidney disease where we are more worried about appetite and nutrition.

      That said, because B vitamins are water soluble and any excesses are simply urinated out, there is no real detriment to supplementing.

      It sounds like you might be giving both a B12 and B complex supplement. I would check the make-up of your B complex supplement. B complex usually includes B12, so you may not need to also give a B12 supplement separately.

  4. Lynette-Higgins

    I have a rescued Sphynx cat. She was rescued October 9, 2023. When I rescued her she weighed only 3 lbs. 8 oz. She was like a walking skeleton. Long story and several vet visits, she now weighs 4 lbs. 6 oz.
    Vitamin B-12 injections have been very helpful. I believe she has IBD along with starvation. The vitamin B -12 has helped her regain her appetite. This article was very informative.