Is changing drugs normal.question to scuba.

Your doctor is incorrect. Changing drugs - even rotating TKI's (start with one drug, change then rotate back) has been shown to provide deeper remission than one drug alone. Theory on this is that each drug attacks CML differently and in a preferential manner.   What this means is that one drug will kill the vast majority of one type of CML cell and a different drug will kill off the others. Rotating drugs is a one-two punch against CML overall and can be a valuable tool to manage difficult CML cases.

https://bmccancer.biomedcentral.com/articles/10.1186/s12885-019-5690-5

http://jnccn360.org/cml/medical-literature/tyrosine-kinase-inhibitor-rot...

From a practical point in terms of side effects - and perhaps where your doctor is coming from, if a single drug works and works well and adverse events are few and well tolerated, it is just fine to stick with one drug. Many patients achieve deep molecular remission taking just one drug. A good reason to switch is if a drug isn't working or the dose needed is too toxic. Switching drugs could lead to new side effects worse than the original prescribed drug. Of course a patient could just return to the old drug if that happens.

Switching drugs both in stochastic models and in observation can lead to response deeper than either drug alone.