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What Are the Most Common Methylcobalamin Side Effects?

By Meshell Powell
Updated Mar 03, 2024
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Some of the most commonly reported methylcobalamin side effects include itching, rash, or diarrhea. Headache, fever, or vomiting may also occur when taking this supplement. Most of the side effects of methylcobalamin are mild, although a doctor should be consulted if symptoms are persistent or become particularly bothersome. Side effects that require immediate medical attention include pain in the lower back or side, difficulty breathing, or facial swelling. Any individualized questions or concerns about potential side effects of methylcobalamin should be discussed with a doctor or other medical professional.

Methylcobalamin, more commonly referred to as vitamin B-12, is naturally found in foods such as meat, dairy products, and seafood. This vitamin may also be taken as a nutritional supplement and is safe for most people as long as the recommended daily amount is not exceeded. In some cases, a person may experience methylcobalamin side effects. Most of these side effects are mild, but medical evaluation is recommended because some of the possible side effects can be fatal.

Abdominal bloating,vomiting, or diarrhea are common methylcobalamin side effects. While these symptoms may occur at normal doses, they are more common when an excessive amount of vitamin B-12 has been consumed. Headaches or a low-grade fever may also be a side effect of taking methylcobalamin. A rash that may or may not itch is another potential side effect, although this is more common when using beauty products such as lotion that contain vitamin B-12 than with an oral supplement.

Anaphylaxis is a medical term used to describe a severe and potentially life-threatening allergic reaction and is among the possible methylcobalamin side effects. Although a rash is a common side effect of this vitamin, if hives develop or the rash is accompanied by other symptoms, it should be treated as a medical emergency. Chest tightness or discomfort may be present along with swelling of the face, lips, or throat. Breathing may become difficult, and the patient may become confused or lose consciousness.

It is important for anyone who is scheduled for a medical procedure such as an angioplasty to let the doctor know if methylcobalamin is being taken. The doctor will most likely advise the patient to stop taking this supplement due to potentially life-threatening side effects. Methylcobalamin is contained in the intravenous fluids used during surgery, and an overdose could occur if a vitamin B-12 supplement is being taken. This medication may not be able to be taken following surgery due to the risks of developing a narrowing of the blood vessels.

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Discussion Comments
By anon937777 — On Mar 06, 2014

Hypokalemia happening. Potassium, your body is depleting those headaches. Look it up. This is common with severe b12 deficiency. Your heart rate drops to healthier levels too. You need to take both. It will feel like b12 deficiency again if you don't keep your potassium up for rebuilding the cell walls.

By lyndennis — On Oct 28, 2013

I have just started a product with methylcobalamin in it. It has other vitamins in the tablet. After three days on this product, my sugars rose, I suffered extreme tiredness, my limbs felt like jelly and I had strokelike headaches. The product is Metaswitch. Would methylcobalamin cause any of these effects?

By anon352749 — On Oct 25, 2013

My doctor give me mecobalamin but I have been sleepless for the last three days.

By amitagrawal — On Aug 03, 2013

It is true. My wife is taking the methylocobalmin 1500 mcg for seven days, and noticed the side effects like dark urine with bad odor, and sleeplessness for the last five days. We will be consulting the doctor in another four or five days.

By anon306222 — On Nov 29, 2012

My doctor advised me to take methylcobalamin and I took it one tab/day. After taking it for three days, I started seeing side effects. Pimples appeared on my face and head, I couldn't sleep, etc.

After seven days of taking this, I went back to the doctor. After examining me, the doctor said to discontinue it. But still I am facing the problems, though they are improved.

By ysmina — On Oct 05, 2012

I think methylcobalamin causes more side effects when it's given intravenously than when it's used as a tablet. It .also causes more side effects in higher doses

I was given a methylcobalamin injection at the hospital once because of a severe deficiency. It caused nausea, vomiting, as well as a rash for a couple of days. After that, my doctor put me on tablet supplements that are a much lower dose than the injection. I didn't get any side effects with the tablets.

If anyone is thinking about getting the injection, you might want to stay at the hospital for a little while in case you get sever side effects. I think it's better to take the tablets if you have the option.

By turquoise — On Oct 05, 2012

@feruze-- Oh yea, that's a normal vitamin B12/methylcobalamin side effect. (And yes, methylcobalamin and mecobalamin is the same thing).

I always get dark urine when I take vitamin B12 supplements and you're absolutely right that vitamin B12 is a water-soluble vitamin. So don't worry, everything will go back to normal when you stop taking it.

By bear78 — On Oct 04, 2012

I've been taking mecobalamin (same thing as methylcobalamin right?) for the past three days. The only side effect I've had is really dark urine. My urine has been looking almost orange and it has a strong odor to it.

I'm assuming that this supplement is water-soluble and that's why I'm getting this side effect. It's not dangerous is it? Should I be worried?

Has anyone else gotten this side effect with methylcobalamin? Please respond!

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