tamoxifen side effects and irregular periods

Hi there. Just a quick question to anyone who knows the answer. I’ve been taking Tamoxifen for just under two years but the last 10 months my periods are all over the place. Mostly they are light, lasting 3 or 4 days, but at least are on time, every 28 days. Sometimes i can go 2 or 3 months without one. But recently ive been getting light periods every 21 days, i.e. every 3 weeks the last two times.

Should i be concerned about periods that occur less than 28 days apart? I ask because I read that ‘unusual bleeding’ could be a sign of something sinister, such as a cancer down below. Am i worrying un-necessarily? I hate to keep bothering my GP. Hope this doesnt seem like a really pathetic question.

Thanks for your help.

Hi Fluffyface.
I’ve been on a combination of tamoxifen and marina coil!!! Periods all over the place but have had it all checked out. There is no such thing as a pathetic question in my opinion, especially when taking a grug with known side effects. Go get checked out ASAP.
Sure everythin is fine.

Worth noting that a lot of ladies on here, me included, have been told that they have to get their Mirena coil removed if their BC is hormone positive. Some oncs say it doesn’t matter but quite a number say it does.
Sarah x


I was told if I didn’t need my Mirena coil as a contraceptive then to have it taken out but if I kept it in then it wouldn’t matter.
Personally I would like to keep it because I don’t know if I have had my menopause or not but I don’t want to be having periods again!


Ditto with the instructions for Mirena coil. I’m having a copper one instead but last time I had one I got really heavy periods. Hoping that doesn’t happen again.

Fluffy, are you still in contact with your BCN? If so, she might be a useful person to call about this, and I’m sure she’ll tell you who to speak to if it’s not her.

I don’t need the coil for contraception as I don’t have OH I just don’t want the periods I’m 51 next week so maybe I have had my menopause but because i had Mirena I don’t know. As I think I understand Tamoxifen you have the symptons of menopause but when you finish the course your body would return to it’s normal state if you were pre menopause. For that reason I don’t think you should rely on it a contraceptive - the leaflet i was given does say not to get pregnant while you are taking it.
I hate messing with hormones and have had lots of problems with the contraceptive pill, and the first 18 months of the Mirena were a nightmare, and I am really concerned that tamoxifen is going to cause more problems unless of course I have had my menopause…

Hello Ladies
Periods, coils and menapause!!! I’ll take on shaving every day. It must be easier being a man.
Regards Chinook
P.S Last period lasted 42 days!!!

I’m with you chinook except that one of the other side effects of tamoxifen is the possible increase of downy facial hair so I may be shaving daily (I wouldn’t really shave I’d see my GP and wear a pink full face balaclava)
I am going to ask my GP if he will fit another Mirena but I have a suspicion he won’t because of my age.

many surgeons are now using the mirena coil in patients on tamoxifen to help reduce the endometrial side effects.

i had my mirena inserted 6 months after diagnosis of strongly ER positive breast cancer and it was a bloody godsend for the horrendous bleeding i was having.

the evidence on the use of mirena and the risk of recurrence is variable… one recent study found that having a mirena inserted after you were diagnosed with ER and/or PR positive cancer does not increase the risk of recurrence.

as for bleeding a cycle of 21 day is not abnormal in itself many people have regular 21 day cycle… if they are always coming at 21 days then this is just the normal for you and isnt classed as irregular if however they are coming at 38 then 20 then 42 days that is irregular… if you feel that your periods are changing ie the frequency is gettings shorter or longer or is becoming irregular or you have heavier bleeding or you have bleeding in between your periods or spotting then its best to get it checked out.

dont know your situation but these can also be signs of chlamydia and other STIs so often your doc will want do a sti screen to rule these out and check that your smears are up to date.

modbird age isnt a risk factor for the mirena… we frequently put them in peri-menopausal women who used it to ease the menopausal side effects… if your GP isnt forth coming contact your local family planning centre and see if they run a menopause clinic and pop along to discuss getting a mirena. (Ps… if your gp doesnt insert coils on a regular basis i would be a bit wary of getting a him to do it… better to get somebody who is expereinced!)

mary grace sometimes periods do stop on tamoxifen but this isnt a given hence the need for reliable contraception… because women ovulate 2 weeks prior to the next period even if you had no periods you could ovulate and get get pregnant without realising.

lulu xx

Hi Lulu34 I’m not concerned about the age factor but when my mirena was fitted they told me to have it taken out when I was 51 because I would have had my menopause and it would have been in for 6 years so reaching the end of it’s life anyway. I would like one to be refitted though because I don’t know if I have had the menopause and I really don’t want to return to a life of irregular very heavy periods that last for ages. Thanks for the info regarding the GP though and I will check and make sure they have an experienced person there as I don’t want any nasty surprises I think I have had enough of those recently.

after age 45 you can keep it in for 7 years as your fertility reduces by then it is found to be effect for longer.

and not sure how they would have been able to predict when you have your menopause… although 51 is the average age some women dont have it til 60.

good luck

How about Pr+ cancer and the Mirena? I’m Er+ 4/8 and Pr+ 6/8 and my surgeon has said “it’s probably a good idea” to remove it. It’s all a worry, as I’ve finally found a method of contraception that I get on with, and now this bloody cancer’s even taken THAT away! Harumph!

ive not had a period at all since i started chemo (fec) in Nov 2009. Ive been on tamox a year. Im 43 now.

I did had a mirena when i was dx with er + BC. So my onc advised me to get the mirena removed.

Hi fluffyface, did you ever check out your irregular periods with your GP?

Only had my light, short period about 2 weeks ago, prior to that one I was late, before that had 2 regular ones, missed one aswell!

I know that my consultant is constantly asking whether I have bleeding in between cycles. Most women on tamoxifen seem to have longer cycles.