Can femara (letrozole) attack the joints?

It causes pain!: Femara doesn't really "attack" the joints, but it definitely causes joint pain! this occurs in 4 out of 10 women taking the drug. It is likely due to lowering of blood estrogen levels. Sometimes switching to another similar drug (anastrazole, aka arimidex) can help. If your vitamin d level is low, getting it back to normal levels with supplements can help the joint pain.

Not "attack": Bone and joint symptoms are a very common side effect of ais (femara/letrozole, arimidex/anastrazole, aromasin/exemestane) typically affecting smaller joints and worse in the morning and improving through the day. If patients can tolerate, the symptoms usually improve with time. They are felt primarily to represent an acute menopausal effect due to the extreme low or lack of estrogen levels.