Hello bitweepy. I'm on Tamoxifen. I'm not sure how much you know, but Tamoxifen is only given to women who have hormone positive tumours. The Tamoxifen interrupts the hormones which feed any dividing cancer cells. If you think of a plant not being watered, it will die and that's the basic theory behind Tamoxifen too, so if you don't feed the cancer cell, it can't grow. In other words, a sanity inducing way to approach Tamoxifen, is to see it as a huge positive, as it's another layer of defence after Op/ chemo/ rads.
On side effects, well some women have none, others have lots. Most of us seem to have menopausal type symptoms. I was 44 when diagnosed (46 now) and have hot flushes and all manner of aches, but I've dealt with it by trying to see Tamoxifen as reducing my risk against recurrence. Let's face it we'll all be menopausal at some point, so mine's just a bit earlier than it would have been.
Sorry for ramble, but hope that helps. Tell your friend to come and say hi if she'd like to. It really helps to talk to other women who've been through it all. This place kept me (relatively!) sane when I was going through treatment. She must be exhausted, but she's on the home run if she's onto rads. 