Cyanocobalamin Side Effects

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My Serum Vitamin B12 was reported as 201 pg/ml at the end of July and the doctor started me on Cyanocobalamin 50mcg tablets two to be taken each day which I take after breakfast - no leaflet in pack saying when to take them.

Since the end of August I have been having two or three loose bowel movements every morning and a feeling of intermittent wind/tickling sensation in my back passage throughout the day. I have not had any pain, bloating, bleeding or mucus and rectal and admiringly examination did not find anything only piles which I already knew about.

Doctor now started me on Mebeverine for IBS to see if it helps.

I suffer from health anxiety and am really worried I have bowel cancer.

Has anyone else had upset bowels after starting Cyanocobalamin?




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6 Replies

  • Posted

    It certainly is listed as a side effect and given it started when you began the medication I would assume that's the cause. Did your doctor say this was a side effect? If you are really concerned you need to have an endoscopy but it would seem to make sense that it is linked to the medication. Maybe it will settle in time. 

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    • Posted

      Thank you for taking the time to reply. My doctor did not mention side effects and there is no leaflet with the medication.  

      I hope you are right and things will settle down, I don't want an endoscopy.


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    • Posted

      If you google the medication side effects come up there I would have a read and reassure yourself. I had injections and can't remember if it affected me. Others on here who suffer will know. Sure someone else will chip in.

      If really worriedspeak to your doc. They should be able to confirm what side effects there may be x

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  • Posted

    Could it be something in the "make up" of the tablets that is upsetting your tummy?

    I would suggest you have a word with your doctor and see if he/she would consider giving you B12 injections as this bypasses the stomach and gets it directly into the bloodstream.

    Do you know why your B12 level was low? Your IBS may be the cause.

    What is your diet like? Are you Vegan/vegetarian? Another possible cause.

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    • Posted

      Thank you for taking the time to reply.

      I am not convinced I have IBS as I only had bowel problems after starting the B12 tablets.

      I will take the one month course of IBS tablets to see if they help but if not I will go back to doctor and ask about having B12 injections.

      I haven't changed my diet and I follow a reasonable healthy diet, not vegan or veggie.

      Worried there is something seriously wrong with my bowels like Cancer, only time will tell.


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