At last I've been given the answer to why ssris and tamoxifen are a poor combination. I was put on tamoxifen as soon as chemo finished and then found a report on the cancer research site that some ssris make tamoxifen less effective. After this being dismissed by senior reg at marsden as "be careful what you read on the internet" I brought it up again at my next appointment and I was then switched to arimidex although a different reg said she didn't know about a link. At my most recent appt I saw the great man himself, Proffessor yarnold and asked if I was on the right drug as I wasn't post menopausal before treatment and have managed to cut down antidepressent to minimum dose. He said that the problem is that an ssri makes the liver work more efficently so the tamoxifen's efficency is slightly compromised as it passes through the body more quickly. He didn't say if this was all ssris or just particular types. IF you are taking an ssri please don't get worried as he also said the effect was quite small so it's a case of weighing up the choices.
I'm pleased that I now understand what the link is but am still irritated that even the senior registrar didn't know about this given the number of patients who are taking ssris for either previously diagnosed mental health conditions or to help with anxiety or depression from being diagnosed with BC.