Rabbi Dr. Akiva Tatz discusses general principles of medical halacha in this lecture. Here are some things that he said that are relevant to your question:
A person is obligated, as a patient, to get the best medical treatment that he can. A doctor is obligated to give the best medical treatment available.
(~50 minutes) You're only allowed to pursue medicine that is widely accepted by broad selections of your generation. That said, what is the definition of "widely accepted"? Conventional Western medicine clearly fits the bill. However, it's not perfect -- there are some things that it's "shockingly poor at." You're allowed to do it, because it's an accepted standard. Homeopathy (though it may not always make sense) is "broadly enough accepted that it's permissible."
(~54 minutes) The first thing to consider is the practical -- has all the homework been done? It's not a good idea to be the first person to use a drug that hasn't been researched properly, to put it lightly. However, according to Rabbi Moshe Feinstein*, if (1) the homework has been done and (2) there is a consensus of expert medical opinion that this is worth the risk, a person is allowed (though not required) to pursue an experimental cure.
Although, of course, these are just the basic rules, and each case needs to be investigated by a rabbi on its own merits.
I strongly recommend that you listen to the lecture; if not for the content, then for Rabbi Tatz's wonderful South African accent :P
* Possibly the teshuva mentioned in my answer here.