Metabolizing tamoxifen

I’m not sure whether I go looking for things to worry about… Since I finished my Zoladex last May I have carried on with tamoxifen apart from a short ‘holiday’ while I was being investigated for endometrial thickening. That turned out to be ok. Anyway I have had two periods since last summer-heavy, not nice- but no hot flashes at all. This could be, apparently, because I don’t metabolize tamoxifen very well. Has any one heard about this and the gene variant (CYP2D6) connected to it? It’s also got something to do with the interaction of some SSRI antidepressants and tamoxifen . Well, I feel a lot better in myself on just tamoxifen. Almost myself pre bc.Onc is muttering about further ovarian suppression because of periods. I am (just) 48 and so could have ovaries out and take AI. Feel uncertain and fed up. perhaps a little knowledge is a dangerous thing? I should be used to the Land of Uncertainty that is bc but don’t like all the maybes. Does anyone have advice, even if it’s just to shut up?!

Love Kitty

Hi Kitty,

I saw your question the other day and thought someone with more knowledge than me may reply so have kept an eye out. I was in the middle of a mini meltdown over the SSRI and metabolizing tamoxifen as I was taking an SSRI at the time (needless to say now I’m not!!!) I did loads of research and it seems that some people dont metabolize tamoxifen as well as others but its only a reduction not it stops it working all together. The SSRI thing seems to be our bodies have to metabolize every drug and some (not all) SSRI’s can reduce the levels of endoxifen (the bit that works in tamoxifen) in some people.

I rang my BC nurse on Tuesday and she has arranged for me to see the oncologist at my 3 monthly surgeon check up on Monday but I’ve stopped taking them anyway now. I’m 39 and having zoladex injections and am planning to have the oopherectomy as will be pre menopausal after the 2 years or sooner if I get fed up with the injections. It seems to be fairly common practice on us er/pr + pre menopausal girls.

I really feel for you on this one as its all stuff thats been flying round my head for a week now so I made the decision to stop the drugs and stop googling too!!!.
There is some really good advice out there on the overy thing from ladies who have had it done or are waiting for it, they helped me hugely but I can kind of get where you are coming from I’m only 3 months into this thing and have decided to delay the oopherectomy for the time being just because I am fed up with feeling rubbish and am just starting to get back on form (apart from peeling hot boob after finishing rads) and want to have a bit of a rest from it (apart from the tamoxifen and zoladex of course).

Good luck with your decision. Sorry I couldnt be much use just didnt want you to feel alone on this one. Love Shonagh xx

Hi Kitty and Shonagh
I did some reading around metabolising issue and the CYP2D6 gene variant. I have to say I found it very hard to make the link from the science to implications for treatment and I think this is because the science is still at a very early stage. Although they know there is some link between the gene and the body’s ability to metabolise tamoxifen, it is not clear if a whole of other things are involved and as I understand it there is no clinical test yet. The link between absence or presence of side effects and efficacy of the drug also seems quite hazy - if you don;t get side effects it could mean that you are not metabolising very well, but there could be many other factors involved. But as I say, I found it quite difficult and may have got things wrong.
I’ve been on Tamoxifen for a month with no side effects…I’m going to have blood tests in June to see if I am pre-or post-menopausal (i haven’t had a period since I was in chemo in Sept) and i guess if I am headed towards post menopausal I’ll be put on Arimidex or similar earlier rather than later.
Like Shonagh I am sorry not to be of more help Kitty but good luck with your decision.

Thanks for your comments, Shonagh and Jo. It helps to know I’m not the only one to go ’ a’googlin’ and , in a sense, be none the wiser afterwards! I’m going to see the onc next month and the doctor who did my hysteroscopy soon afterwards. Will decide then. As my GP said, tactfully, I suppose: “It’s not an exact science!”

Best wishes


yes, it is amazing how inexact some of it is! the onc team at my hospital clearly think this is one area where any claim to certainty has to be thrown out of the window. i’d be very interested to hear what your onc says kitty. hope the meeting goes well.