Yes, I’ve had side effects from Kisqali and Letrozole but let me preface my response noting I’m highly sensitive to meds and almost always have adverse side effects. I’m always a medical outlier.

Kisqali 600 -starting dose. 4% of people get prolonged QT which is a very dangerous heart rhythm detected by an EKG. I was one of those people right off the bat. Healthy heart. I could hardly walk across the room on that dose. Med stopped till normal rhythm then reduced dose to 400 and PQT stopped. But I’ve also been going into afib since week one and didn’t have it before. That’s my most dangerous and worrisome side effect although apparently not a common one. It has caused a few TIAs and causes total weakness and fatigue on those days.

Others are fatigue, hair thinning, lower blood pressure, low blood counts reduced immune system, aggravates my neuropathy. Letrozole also causes fatigue and hair thinning. Oncologist says the Letrozole is responsible for my sporadic knee and shin pain. I also believe it has caused my insomnia which is a documented side effect. Fatigue was the worst year one. I could hardly stay awake. Year two next worst. Still have fatigue issues but I’m not falling asleep all the time. The afib has worsened each year in frequency and duration. Having said all that, I’ve continued to take these meds as it beats the alternative! 😊 It’s just the new normal just like aging is our new normal.

Note 2 months after starting these, I started another med for neuroendocrine lung cancer and still take it. It causes some of the same side effects and others so that muddies the water.

Everyone reacts to meds so differently I wouldn’t assume this would be anyone else’s experience. I don’t even tolerate vitamins well.