I have been on tamoxifen for just over a year without any major problems - just mild hot flushes which seem to be lessening over time. Sometimes I wonder whether my early waking is due to the drug but possibly it's just me. I take mine in the morning - I thought it would be less likely to affect my sleep that way. But it probably doesn't matter when you take it. i certainly haven't had any muscle fatigue while taking it (except when I have done strenuous exercise and you would expect to get muscle fatigue.) Good luck with it. I hope it is better for you than the arimidex. Janet.