I do not take Letrozole. However I am on Anastrazole and occasionally get mild nausea. It tends to happen if I don’t take it with a little food. Both drugs have very similar potential side effects.
Is your Oncologist thinking it is due to something else for a reason? I am surprised that they would not acknowledge that letrozole could be the culprit as it should be stated on the Patient Info Leaflet enclosed with the tablets. Perhaps show the Onco that. Otherwise, you will see it listed on this site. See below:
Info from BCC site:
8. Less common side effects of Letrozole
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Headache, nausea and vomiting
Letrozole can sometimes cause headache, nausea (feeling sick) and vomiting (being sick). While many people find that these problems will improve over time, talk to a member of your specialist team or as they may be able to offer suggestions that will help. Simple pain relief such as paracetamol may help with headache, and anti-sickness medication can be prescribed if you have nausea or vomiting. Taking your letrozole with or after food can help reduce nausea.
Below is from a Letrozole Patient Information Leaflet:
I have been on letrozole for about 18 months. I had nausea at the start, but not anymore. I switched from taking it in the morning, to the evening, which definitely helped. Also, I understand it’s better to take with food.
I seem to have many of the other side effects though, so it is an on going challenge!