I did my first six months on Letrozole. I'd get sudden onset migraines lasting for 10 hours or more. Lethargy plus lower back pain. Been 6 months on Anastrozle now. Only mild headaches now and then. Energy returned. Sore back on the other side now. I did have the sore thumb and base of thumb, plus the trigger. Bought a figure 8 to hold the thumb out. I could do anything pain free but when I took it off it was even more painful. It was a mixed bag. I rubbed Voltaren cream around my thumb and got some relief. I also started taking Glucosomine, 1 a day. Arthritic people seem to benefit from it so maybe I am too. I had an ultrasound on my thumb and was told the tendon is thickening. Injections or an op was the solution. Well that must have scared the crap out of my thumb as it immediately started getting better. It's been nearly 3 weeks and I can bend the top of my thumb with only a twinge. The base pain has gone too. The pharmacist told me that Anastrozle can cause carpel tunnel.