Pernicious Anaemia Society
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A question for the girls :-) - B12 injections and periods, advice please

Hi, I have just had my first loading dose of B12, and started my period yesterday, normally I hardly notice these but this time I have painful cramps and am a lot heavier than usual.

It could be anything of course, but wondered if this is normal on B12, or when you first start?

also am feeling super rotten today, finding it hard to catch my breath, lots of aches - I think a lot of people fel tis way on their periods, I have heard all sorts of tales over the years and thought myself lucky to have really easy ones.

8 Replies


I have had really bad heavy periods for the last few years and low b12 was thought to be part of the problem, I was recently put on the pill to control them (which does make them a bit lighter but I am getting bleeding when I shouldn't!). I started my B12 injections at the same time as the pill so don't know if they counteracted each other but I was under the impression having b12 should make periods easier. Hope next month is better for you!


Hi serendipity16,

Thank-you for your reply. I am sorry to hear you have suffered from bad periods - I have heard all sorts from other ladies over the years and it really does impact on your life.

As for the pill - I have not had a good experience myself - it just did not do good things for my body, however I have heard in younger women it does marvels for regulating periods - so am surprised you are getting intermittent bleeding - worth another poke at the docs perhaps?

wishing you pain free times :-)



Thanks, I was back yesterday but as the bleeding is starting longer after each pack I've to try another three months and see if it settles (2nd pack had 9 period free days, 3rd pack 13- the doctor reckons in three months I should get my full 3 weeks free). Her other recommendation was running two packs together but if the bleeding starts after two weeks I dont see the point! I'm not a fan of the pill and got cervical erosion for the 1st time the 1st of three attempts on it so generally have not been very optimistic. Giving it one last go. Hope you have pain free times too.


You may find that like me, they are a different to normal for a while. I was pushed into an early menopause at the age of 40 because of undiagnosed PA, the Dr feels that it had been part of my problems for many years. Also auto immune disorders can mess with cycles or do as it did to me.

After a few months of weekly injections, I was permitted to get such regular injections as my levels were so low and I was really suffering, my cycle suddenly regularised even though my hormone levels showed I was in early menopause. Give your body time to settle and things should sort themselves.


Hi Luna,

early menaupause sounds challenging! Glad to hear your cycle sorted itself out though.

I am asking because my body seems to be falling apart right now and am trying to sort out symptoms into the thyroid, fibro, PA, slipped disc and unknown baskets - that way I can help my doctors help me get the treatment I need.

Big hugs,


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Strangely enough my daughter who is on B12 supplements, had significant improvement to her periods that were usually very heavy. Now they are what she calls normal. Maybe what B12 does is allow Red Blood Cells to be 'built' up to a normal level for a woman your age. I have heard that B12 have improved people's fertility, so maybe heavy periods is what should be normal for you... As to the aches and pains, breathlessness etc, this could be due to B12 needing potassium to build RBC, so I would check out low potassium symptoms and eat a banana or maybe two until you have fathomed it out.


Hi Dovechick,

I love the fact you think I should be fertile at my age - I cannot even begin to think what having another child now would be like - LOL ;-)

there is an outside chance it might be theoretically physically possible for me at 40 but I bow down at the feet of women who do - they must be super energetic ! :-)

I do have a banana smoothy each day ( 1 banana, 2 tablespoons raspberry yoghurt, some milk) - so hopefully this would offer me the potassium.

I read on the B12 website that potassium, ferratin (iron) and folate are important in making your B12 injections do all they can for you so will try to get the docs to keep an eye one these.

Big hugs



I can't say that I've noticed any effect on my periods as a result of B12 injections - started last year.

I'm now in my 50s and they are starting to get a bit irregular but in terms of pain - used to be bad when I was younger but started taking an iron supplement when I was in my 30s and that seemed to sort things out. Occasionally I get one with cramps but for the most part I don't really suffer on that side ... anxiety on the other hand tends to go through the roof these days :) but that's built up in my 40s and I don't think it has anything to do with the B12.

Hope you feel a bit better from the top-ups soon.


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