I have done the IBDP and my extended essay was directly related to the general area of medicine - it involved medication, its synthesis, etc. (did mine in chemistry)
From the interviews I attended, not once have I been asked about the content of my EE (despite mentioning it in my personal statement). It did show my commitment for medicine and my interest in it, but I doubt it was make-or-break in terms of my application. For all it's worth, when attending the open day and talking to a DoS at one of the unis I applied to about my EE, I was told it's an interesting subject and topic, but I should only mention it if I really think it's linked to the rest of my PS.
You COULD, however, get questioned about it during your interviews. Some unis do PS-related interviews, and you have to know your topic through and through. Do it in a subject you are genuinely interested in rather than in something that might look good on your personal statement. Without actively mentioning what you did your EE in, the unis won't even know which subject you did yours in.