I have discovered that a higher premium may be required if one is taking an anticoagulant after having had a stroke (and possibly without a stroke experience). Thus, although anticoagulation is considered to reduce the risk of a serious medical episode, it may increase the likelihood of a major travel insurance claim in the eyes of the underwriter.
I made this discovery by accident. One of the medical questions originally asked upon application was: "Are you on medication to thin the blood (excluding aspirin and clopidogrel)?" For reasons unknown the answer "No" appeared in the subsequent insurance documentation. When I reported that I was taking Apixaban, I was advised that a significantly higher premium was payable, without which the insurance would be invalid.