Medicine essays are complicated enough to write as it is, but the fact that it's always changing and is always advancing is something that makes it even more complicated. Writing essays on medicine prompts the age old debate between whether including the new and discarding the old is acceptable, regardless of whether the official syllabus has updated itself or not.
Controversy is good when writing an essay for a medicine degree since it's a field that's always open to new ideas from creative and innovative doctors. Most essay subjects believe the same thing. Writing an essay on a controversial subject shouldn't be attempted unless the evidence is there to back it up, though. It's taking a massive risk and any holes will look ten times worse when speaking of a topic that isn't looked at as gospel in the medical world. Furthermore, examiners who feel strongly one way or the other will be scrutinising it with a careful eye when it comes to a subject that's close to their hearts.
These subjects are for the students who really want to aim high and achieve a lot, so only attempt it under the correct circumstances. A subject that doesn't have a lot of information on it should be avoided as it's going to be difficult to argue for it when there are blatant flaws in it.
When deciding on including a controversial source or not take a look at the question. Checking how specific it is can answer the question when concocting essays on medicine as medicine essays can come in either form. If it happens to be asking about a revolutionary technique then a passing comment on how it's evolved since then shouldn't be avoided. On the other hand, if it asks the student to talk specifically about that technique then mentioning something new wouldn't be prudent.
Writing an essay for a medicine degree will bring up a lot of sources from a lot of locations. Not every source out there is reputable or well-respected. When speaking of medicine it's all about the science itself. So writing an essay for a medical degree and bringing in a source from an alternative medicine book wouldn't help as alternative medicine generally isn't accepted by the medical community. Regardless of how convincing it is, don't risk using it or it could just lead to problems in the future.
Another point has to be made on sources. Controversial subjects are controversial as it doesn't have a full argument that supports it. If it did then there would be no discussion about it. Students will often find that they start researching a subject and then they discover some sources that convince them that there's an entirely different side to the argument, and thus that blows their whole plan out of the water. It's a risk that's often taken, so be careful when choosing a controversial subject to write about.