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Vitamin B12 Injection Cats Side Effects : B12 is water soluble and has the most extensive and complex chemical structure of any vitamin.
The list of advantages and symptoms of deficiencies is lengthy.
B12 supports adrenal function, keeps the nervous system healthy, aids in the production of DNA and RNA, and aids in the production of neurotransmitters.
It has an impact on the formation and maintenance of red blood cells, nerve cells, and normal myelination (the fatty sheaths that cover and protect nerve endings).
It is required to prevent anemia, as well as for proper digestion and absorption of food, as well as the metabolism of carbohydrates and fats.
A B12 deficiency can result in nausea, vomiting, loss of appetite, poor absorption of food (malabsorption syndrome), constipation, gas, weight loss, fatigue, lethargy, abdominal pain, and/or diarrhea.
Normal stomach, pancreas, and small intestine function is required for B12 absorption.
These are the symptoms that cats suffering from IBD and other gastric disorders exhibit.
A B12 deficiency also inhibits and reduces the body’s ability to produce blood, increases blood cell destruction, and is extremely harmful to the nervous system, resulting in neurological disorders and severe, sometimes irreversible nerve damage.
Because a healthy liver can store many years’ worth of B12, symptoms of deficiency may go undetected for a long time.

Vitamin B12 Injection Cats Side Effects

Because vitamin D is a water-soluble vitamin excreted in urine, “clinical disease due to over-supplementation should not occur and has never been described in any species,” according to Texas A&M Veterinary Medicine and Biomedical Sciences.

However, because it contains cobalt, it may cause allergic reactions in your pet if it is sensitive to cobalt.
Fortunately, such hypersensitivities are extremely rare.

Finally, because it is a water-soluble vitamin, any excess amounts will be excreted in your pet’s kidney and excreted through urine.

Side effects in cats have been found to be very similar than in humans.

Just as it is critical to understand the benefits of the B12 shot, it is also critical to understand the B12 shot side effects.
Before anyone makes a health-related decision, it is critical that they understand both the risks and the benefits.
Understanding both the B12 shot side effects and the B12 shot side effects at the injection site is important because it allows you to make an informed decision about your treatment.

Side effects of B12 shots include, but are not limited to and some may be more or less prominent in cats than in humans:

  • Vitamin B12 is essentially non-toxic but it should not be given to animals with known hypersensitivity to it or to cobalt. Anaphylactic shock and death have been reported in humans following administration of vitamin B12 by injection
  • Swelling at the injection site
  • Mild diarrhea
  • Itching
  • Swelling in the body
  • Low potassium
  • Headache
  • Dizziness
  • Vomiting
  • Skin rash
  • Pulmonary edema and congestive heart failure (in early treatment)
  • Vein thrombosis
  • Polycythemia vera
  • A very rare, but serious allergic reaction causing swelling of the face, tongue, and throat, and difficulty swallowing or breathing (anaphylaxis)
  • Restenosis
  • High blood pressure immediately after injection
  • Cold symptoms
  • Anxiety
  • Burning skin
  • Pink or red skin discoloration
  • Joint and muscle pain
  • Facial swelling
  • Numbness
  • Increase and blood volume and red blood cells

When considering the B12 shot side effects listed above, it is important to remember that some of these side effects are more common than others.
When evaluating your diagnosis and considering treatment, this is another important topic to bring up with your Vet.

A weakened immune system and impaired white blood cells, gluten allergies and/or sensitivities, and helicobacter pylori infection are all risk factors for B12 deficiency (a bacteria that can be common in IBD)
Antacids, H2-blockers, anticoagulants, and potassium supplements can all impair B12 absorption, as can the use of broad-spectrum antibiotics or anticonvulsants, as well as parasites (specifically tapeworm).
Large parasites, such as the beef tapeworm, compete for nutrients by depleting the body of micronutrients and vitamins.

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Concerning B12 injections for cats, there has been much discussion about cyanocobalamin vs methylcobalamin.
This is understandable given the complexities of the subject.
Given that methyl is a bioactive form and cyano is not, there is a lot of marketing promoting methylcobalamin as a superior supplement to cyano.
Yes, cyano is converted by the body into bioactive forms, as discussed further below.
Methyl is primarily used in the liver, brain, and nervous system and is required for proper nervous system health.
Although high blood levels of vitamin B12 are common in people with liver disease, it is not uncommon to have a correspondingly low liver tissue concentration of vitamin B12 and its enzymes.
Methyl B12 should be used for liver conditions because it helps the liver function much more efficiently.
All neurological diseases, including diabetic neuropathy, should be treated with methyl.
Cats with this condition are now receiving at least 3,000 mcgs of Methyl B12 per day, with amazing results!

In terms of using methyl instead of cyano for GI diseases, there is no evidence that methyl works better, and methyl actually breaks down faster and contains more preservatives than cyano.
You’re looking for something with staying power, something with a longer shelf life in the body.
Methyl B12 injections contain the same amount of benzyl alcohol as cyanoB12 injections, if not more.
There are no side effects to any of these injections, so use caution at all times.
Do your homework and make sure your vet is aware of what you’re giving your cat.
B12 injections are illegal to obtain without a prescription in the United States, and it may be tempting to give your pet a dose of the human version or one that has been mixed without a prescription.
However, I would not recommend it.
The human version may have more preservatives, and if obtained without a prescription, it is most likely counterfeit B12 mixed with who knows what.
It may contain toxins of some kind and may not even contain the proper dosing of B12, putting your pet’s health at risk inadvertently.
It has also been questioned whether supplementing with B12 masks the symptoms of diseases and malabsorption syndrome.
My veterinarian believes it does not, but even if it did mask symptoms of IBD, pancreatitis, and other diseases, it shouldn’t matter.
All medications are designed to mask symptoms.
That’s what they do to help the body heal itself.
To heal itself, you want the cat to feel less pain and eat more.
It is up to the owner to be diligent about testing on a regular basis.
B12 will not affect the results of IBD or other conditions’ tests.
When a patient improves, any treatment for any disease will mask the disease’s underlying problems.
The blood work and testing results are what determine whether or not the patient is healing.
I would have started Alex on B12 sooner if I had known how important it is and how quickly and effectively it helps cats with many diseases, not just IBD or malabsorption issues.
I only learned about it near the end of her life, and by the time I started the injections, it was indeed helping, but it was too late.
As a result, I believe it is critical to have them tested for deficiency at the first sign of illness.
It was once thought that dosing anyone, human or animal, with B12 without first testing would be safe.
Recent studies have found high levels of B12 in cancer patients, prompting the B12 to be blamed.
However, the studies are flawed, and experts agree that high B12 levels are most likely caused by cancer rather than the other way around.
According to the researchers, “an increased vitamin B12 level makes sense for cancers associated with high alcohol intake, such as liver cancer.”
Cancer of the liver would impair the liver’s function, and since the liver processes vitamin B12, it stands to reason that the patient would have high levels of vitamin B12.”
And, while we’re talking about cats here, and they almost certainly don’t drink alcohol, IBD is associated with an increase in liver diseases, which could result in higher B12 levels if the liver function is impaired.
If you’ve never given a cat an injection before, don’t try it on your own.
Allow a veterinarian to demonstrate how to administer the injection and, if possible, have him observe you administering your first injection.
Although complications from a bad injection are uncommon, they can kill your cat.
An air bubble in the bloodstream, as well as a dose of medicine in the blood that is meant to be administered through the skin, can be fatal.
So it’s better to be safe than sorry and have a professional assist you with your first few injections.
Even having the assistance of someone who is familiar with animal shots is preferable to attempting to do it on your own.
The good news is that once you’ve done it a few times, it becomes very easy to do from then on.

Cautions for Vitamin B Complex

The US Food and Drug Administration (2017) warns that taking large doses of biotin supplements in humans may have an adverse effect on T4, T3, and parathyroid hormone test results (PTH).

Alpha lipoic acid is toxic to cats, so avoid products containing it.
Elderly cats have increased vocalization (2015)
Gunn-Moore & Co.
According to the European Journal of Companion Animal Practice 25(3), pp20-29.
“Because alpha-lipoic acid is toxic to cats, products containing it should not be given.”

I used to recommend NutriVed, but I recently discovered that it now contains propylene glycol, which is safe for dogs but not allowed in cat foods because it can cause red blood cell abnormalities, which is not what you want in an anaemic cat.
Propylene glycol: teach yourself and your veterinary clients about it (2015)
Propylene glycol is discussed further in Scheidegger S DVM360 Magazine.

Hi-Vites and Felovite II are multivitamin supplements made in the United States.
There is nothing wrong with these products in and of themselves, but they are too high in vitamin A and D for a CKD cat, and Felovite II contains phosphorus.
Several cats on the support group, in particular, have performed poorly on Hi-Vites.

Candioli’s Aventi KP Kidney Support (formerly Renal Advanced) is a product that is widely available in Italy and Canada.
There is some information about it on Drugs.
It contains probiotics as well as vitamins B6, B12, and B9 (folic acid).
It does, however, contain prebiotics in the form of fructooligosaccharides (FOS), which may raise calcium levels in some people.
Personally, I would only use B vitamins and supplement with a probiotic if necessary.

Renal Essentials is another product that contains a few B vitamins as well as other ingredients such as extra potassium.
Not all CKD cats require additional potassium, but if yours does, there is likely insufficient potassium in this product to make a difference.
Again, I would simply use B vitamins and supplement with potassium if necessary.

Deficiencies in Vitamin B12

Vitamin B12 deficiency can be found in patients suffering from a variety of conditions.

Cats with IBD or pancreatitis have low cobalamin levels.

Hypocobalaminaemia is common in cats with spontaneous hyperthyroidism (2011)
Cook AK, Suchodolski JS, Steiner JM, and Robertson JE discovered that a significant percentage of cats with hyperthyroidism have low cobalamin levels in the Journal of Small Animal Practice 52(2) pp101–106.

In cats with cardiomyopathy and arterial thromboembolism, plasma homocysteine, B vitamins, and amino acid concentrations were measured (2000)
McMichael MA, Freeman LM, Selhub J, Rozanski EA, Brown DJ, Nadeau MR, Rush JE discovered that cats with heart disease who have arterial thromboembolism (saddle thrombus) have significantly lower levels of vitamin B6, vitamin B12, and arginine, an amino acid.
“We interpret the results of this study to suggest that vitamin B12 and arginine may play a role in CM and ATE in cats,” the study concludes.
If your cat has heart disease, you should talk to your vet about using methylcobalamin.

Vitamin B12 deficiency may be especially problematic in senior cats.
a lack of vitamin B12 (2003)
According to OH RC & Brown DL American Family Physician 67(5) pp979-86, one study discovered that 15% of people over the age of 65 had a vitamin B12 deficiency.
Taking care of age-related changes in feline digestion (2010)
According to Patil AR and Cupp CJ of the Nestlé Purina Companion Animal Nutrition Summit 2010 Focus on Gerontology, “if Vitamins E and B12 levels are low, then fat and protein processing in older cats is likely compromised.”
The effect of age, gender, and body weight on serum cobalamin and folate concentrations in cats fed a consistent diet (2018)
Hill SA, Cave NJ, and Forsyth S measured cobalamin and folate levels in cats of various ages and concluded that “this finding suggests that older cats, independent of diet, are at an increased risk of cobalamin deficiency.”

Vitamin B12 is also frequently recommended for diabetic neuropathy in cats.

Potassium and vitamin B12

Workup for Vitamin B-12-Related Neurological Diseases (2016)
According to Singh NN Medscape, when patients with vitamin B12 deficiency and severe anaemia are given vitamin B12, “hypokalemia [low potassium levels] may develop due to increased potassium utilization in hematopoiesis.”

Most CKD cats do not have a cobalamin deficiency in the traditional sense, and
I treat cobalamin (vitamin B12) deficiency in the following ways: (2008)
According to Carmel R Blood 112(6) pp2214-2221, such drops in potassium levels are typically transient and “its clinical relevance has never been proven.”
Before beginning methylcobalamin, consult your veterinarian if your cat already has severe anaemia and low potassium levels.

Cancer and Vitamin B12

A cross-sectional study found that hypercobalaminaemia is associated with hepatic and neoplastic disease in cats (2014)
Trehy MR, German AJ, Silvestrini P, Serrano G, and Batchelor DJ BMC Veterinary Research 10 pp175 investigated elevated cobalamin levels in cats who had not received vitamin B supplementation and concluded that “the current study has suggested possible associations between hypercobalaminaemia and the presence of either solid neoplasia or liver disease in cats.”

According to Immunohistochemical quantification of the cobalamin transport protein, cell surface receptor, and Ki-67 in naturally occurring canine and feline malignant tumors and adjacent normal tissues, it may be prudent not to give vitamin B12 to a cat with cancer because cancer cells rely on vitamin B12 for growth (2015)
Oncotarget 6 pp2331-2348, Sysel AM, Valli VE, and Bauer JA state that “Cancer cells have an obligate need for cobalamin (vitamin B12) to enable DNA synthesis necessary for cellular replication.”

Update on the Purina Pro Club (2013) 12 (1)
According to Dr. Sysel of the Bauer Research Foundation “Vitamin B12 is essential for DNA synthesis because cells cannot divide without it.
Rapidly growing, actively dividing tumors have an especially high demand for vitamin B12.
Tumor cells produce TCII [transcobalamin, a protein that transports vitamin B12 through the bloodstream] in order to obtain as much vitamin B12 as possible.”

However, researchers are also investigating whether cancer cells’ need for vitamin B12 can be used to target cancer.
Cobalamin transport protein, cell surface receptor, and Ki-67 immunohistochemical quantification in naturally occurring canine and feline malignant tumors and adjacent normal tissues (2015)
“The potential to use these proteins as biomarkers to identify neoplastic tissues, streamline therapeutic options, evaluate response to anti-tumor therapy, and monitor for recurrent disease has important implications in the advancement of cancer management for both human and companion animal patients,” writes Sysel AM, Valli VE, and Bauer JA in Oncotarget 6 pp2331-2348.

A stability-indicating HPLC method for the determination of nitrosylcobalamin (NO-Cbl), a novel Vitamin B12 analog (2014) Dunphy MJ, Sysel AM, Lupica JA, Griffith K, Sherrod T & Bauer JA Chromatographia 77(7-8) pp 581-589 reports on the use of nitrosylcobalamin “as a biologic ‘Trojan horse,’ utilizing the vitamin B12 transco

The University of Pennsylvania School of Veterinary Medicine has been investigating whether cats with lymphoma may have a vitamin B12 deficiency (which is possible because lymphoma may reduce vitamin B12 absorption in the intestines), and if so, they plan to provide supplemental treatment to address the deficiency.

Diabetes and Vitamin B12

Methylcobalamin is commonly given to diabetic cats in relatively high doses.
However, Effect of B-vitamin therapy on diabetic nephropathy progression: a randomized controlled trial (2010)
House AA, Eliasziw M, Cattran DC, Churchill DN, Oliver MJ, Fine A, Dresser GK, and Spence JD discovered in the Journal of the American Medical Association 303(16) pp1603-1609 that humans with diabetes and kidney disease caused by diabetes who were given three B vitamins (25mg/d of vitamin B6 (pyridoxine), 2.5mg/d of vitamin B9 (folic acid), and 1mg/d of vitamin
“Because these vitamins are water-soluble and renally excreted, vitamin toxicity may be more of a concern in patients with impaired renal function,” according to the study.

Cats with diabetes are typically given methylcobalamin for up to three months, until the diabetes is under control, whereas the humans in this study were given cobalamin for 36 months.
It is also unknown which form they were taking, but it was most likely cyanocobalamin.
Apart from B vitamins, these patients had severe diabetes and advanced CKD and were receiving multiple treatments.

I would not give your CKD cat more than 1 mg per day, and I would feel more comfortable giving 500mcg (0.5mg) only.
Consult your veterinarian to determine the best dose for your cat.

Taking Human-Sized Vitamin B Complex Capsules and dividing them into Cat-Sized Doses

I’ve been asked numerous times how to divide the small amount contained in these capsules into ten.

Empty the contents of the capsule onto foil and cut it into ten pieces with a knife or razor.

Divide the capsule contents into ten equal parts in a shallow bowl or plate.

Make use of measuring spoons.
These are covered in this section.
The size of these spoons varies depending on the manufacturer, but the drop spoon apparently holds about a tenth of a Jarrows B-Right capsule and the smidgen spoon apparently holds about an eighth of a Jarrows B-Right capsule.
To determine which size spoon to use, divide the capsule contents into ten, then tip a tenth into the spoon you think might work; however, once you’ve decided which size spoon to use, you can simply scoop up enough powder to fill the spoon.

If possible, divide the daily dose further into 2-3 doses per day, but this is difficult in practice due to the small amounts involved.
As a result, after dividing the original capsule contents into ten cat-sized doses, most people find it easiest to decant the portions into ten empty gelatin capsules and administer one capsule once daily.
People who divide their dosage on foil pieces can carefully tear the foil and fold it into a funnel shape, which they can then use to pour the powder into an empty gelcap.
Others prefer to purchase a small funnel designed specifically for this purpose.
Members have used this Torpac one or found them in the United States at Bed, Bath, and Beyond for around $2.

One person discovered that if she emptied the contents of a Jarrows B-Right capsule, the correct cat-sized dosage (one tenth of the original capsule) filled one half of a size 5 gelcap to the top, so she simply scooped up the powder with the empty size 5 gelcap.
If necessary, she could add other medications to the capsule by squashing the powder with the additional medications.


What is Vitamin B12?

Vitamin B12, or cobalamin, is important for nerve cells, energy production and red blood cell production.

What are the different conditions?

Cats with IBD or pancreatitis tend to have low levels of cobalamin.

What are the effects of arterial thrombus on cats?

Plasma homocysteine, B vitamins, and amino acid concentrations in cats with cardiomyopathy and arterial thromboembolism (2000) McMichael MA, Freeman LM, Selhub J, Rozanski EA, Brown DJ, Nadeau MR, Rush JE Journal of Veterinary Internal Medicine 14(5) pp507-12 found that cats with heart disease arterial thromboembolism (saddle thrombus) have significantly lower levels of vitamin B6, vitamin B12 and arginine, an amino acid.

What are the tests you can use?

Early Detection Blood Chemistry: Kidney Function, Potassium, Other Tests (ALT, Amylase, (Cholesterol, Etc.) Calcium, Phosphorus, Parathyroid Hormone (PTH) and Secondary Hyperparathyroidism Complete Blood Count (CBC): Red and White Blood Cells: Anaemia and Infection Urinalysis (Urine Tests) Other Tests: Ultrasound, Biopsy, X-rays etc.

What are the symptoms of CKD?

Which Tests to Have and Frequency of Testing Factors that Affect Test Results Normal Ranges International and US Measuring Systems TREATMENTS Which Treatments are Essential Fluid and Urinary Issues (Fluid Retention, Infections, Incontinence, Proteinuria) Waste Product Regulation (Mouth Ulcers, GI Bleeding, Antioxidants, Adsorbents, Azodyl, Astro’s CRF Oil) Phosphorus, Calcium and Secondary Hyperparathyroidism (Calcitriol) Phosphorus Binders Steroids, Stem Cell Transplants and Kidney Transplants Antibiotics and Painkillers Holistic Treatments (Including Slippery Elm Bark) ESAs (Aranesp, Epogen etc.) for Severe Anaemia General Health Issues in a CKD Cat: Fleas, Arthritis, Dementia, Vaccinations Tips on Medicating Your Cat Obtaining Supplies Cheaply in the UK, USA and Canada Working with Your Vet and Recordkeeping DIET & NUTRITION Nutritional Requirements of CKD Cats The B Vitamins (Including Methylcobalamin) What to Feed (and What to Avoid) Persuading Your Cat to Eat 2007 Food Recall USA FLUID THERAPY Oral Fluids Intravenous Fluids Subcutaneous Fluids Tips on Giving Subcutaneous Fluids How to Give Subcutaneous Fluids with a Giving Set How to Give Subcutaneous Fluids with a Syringe Subcutaneous Fluids – Winning Your Vet’s Support Dialysis RELATED DISEASES Heart Problems Hyperthyroidism Diabetes Polycystic Kidney Disease (PKD) Pancreatitis Dental Problems Anaesthesia OBTAINING SUPPLIES CHEAPLY UK USA Online USA Local (Fluids) Canada SAYING GOODBYE The Final Hours Other People’s Losses Coping with Your Loss MISCELLANEOUS Prevention Feline CKD Research, Including Participation Opportunities CKD Research in Other Species Share This Site: A No

What are the benefits of eating healthy?

Appetite Brain Health Gastrointestinal system Nerve system

What are the symptoms of cats with diabetes, heart disease or thyroid problems?

Diabetes IBD Pancreatitis Sick or unwell cats who won’t eat Renal Disease Hyperthyroidism Heart Disease (if your cat is drinking a lot for any reason it can lead to B12 deficiency)

What are the symptoms of lethargy?

lethargy vomitting off food / weight loss confused trouble walking or jumping

What is B12 for cats?

For sick cats the most important thing B12 does is give them their appetite back and just generally make them feel better.

What is a B12 shot for cats?

B12 is also known by the name Cobalamin so don’t get confused if you see that term thrown around online.

What if your cat doesn’t have fingers?

True, if the roles were reversed your cat wouldn’t do the same for you but that’s only because they don’t have fingers.

What is B12 shots?

Tips Cooking Cleaning Chickens Decorating Etiquette Fixing Gardening Health & Beauty Organizing Technology Blogging DIY DIY Tutorials Christmas Easter Halloween Valentine’s Day Flower Arranging My Life Me My Family Books I Read TV I watch Product Reviews Random Stuff Giving Your Cat a Vitamin B12 Boost. Giving your cat a B12 shot is a really inexpensive way to make a sick cat feel better quickly.

What was the treatment for my cat?

Giving your cat a B12 shot is a really inexpensive way to make a sick cat feel better quickly.

What should I feed my cat?

In the meantime try to find something, ANYTHING that your cat will eat.

How do I inject B12?

If you’ve tried everything take your vet to the cat and also ask them about B12 How to Give Your Cat a B12 Shot Don’t give your cat a B12 shot without consulting your vet first.

What are your concerns?

Any known health issues.

What are the effects of B12 shots on cats?

I have not noticed any changes in feces or in insulin neds for the one diabetic cat that gets the shot.

What are your concerns?

I have suspicions that because most kitties respond well to B12 injections whether they test normal or not, that an imbalance/deficiency of B12 or other B vitamins in their diet is contributing to a possible cause of IBD.

What are the culprits?

Over-processed pet food could be a possible culprit in a lot of these deficiencies, dry food being the worst of the offenders.

What are the ingredients in cat food?

Not much meat and if there is, it’s usually meat meal, meat by-products, meat filler.

What is B12?

By Lisa Provost B12 is water soluble and has the largest and most complex chemical structure of all vitamins.

What are the symptoms of a B12 deficiency?

A B12 deficiency can cause poor cell formation in the digestive tract and lead to nausea, vomiting, loss of appetite, poor absorption of food (malabsorption syndrome), constipation, gas, weight loss, fatigue, lethargy, abdominal pain, and/or diarrhea.



  • The human body has roughly a 3-year supply of B12 and 30% of that found in food is typically destroyed by cooking. (
  • The human version may contain more preservatives and if it’s obtained without a script, it’s most likely counterfeit B12 and mixed with who knows what. (
  • But the studies are flawed and experts are agreeing high B12 levels are most likely caused by cancer, not the other way around. (
  • These individuals will likely have to supplement their diet with an oral B12 supplement or a B12 injection. (
  • Save up to 80% on your prescription with Selected from data included with permission and copyrighted by First Databank, (
  • According to the World Small Animal Veterinary Association World Congress Proceedings, 2014 , a typical dosage amount is 250µg of cobalamin per dose. (
  • Each mL of sterile aqueous solution contains: Cyanocobalamin (B12) 1000 mcg with sodium chloride 0.22% w/v, ammonium sulfate 0.1% w/v, citric acid 0.01% w/v, sodium citrate 0.008% w/v, and benzyl alcohol 1.0% v/v (preservative).
  • If your cat suffers from chronic digestive or gastrointestinal problems, oral B12 supplements are unlikely to help. (

Scholar Sources

Efficacy of intramuscular hydroxocobalamin supplementation in cats with cobalamin deficiency and gastrointestinal disease

Hereditary diffuse gastric cancer: updated clinical practice guidelines

Idiopathic inflammatory bowel disease in cats: Rational treatment selection

Feline hepatic lipidosis

Vitamin B12 Injection Cats Side Effects