It is hard to find the time to check the literature. Often you want the answer immediately. It is tempting to rely on one or two sources, because any venture further afield into the literature shows that a lot of the evidence is contradictory. Unfortunately, you are not going to find the evidence in one, easily obtainable package, nor will it be in one place. You will need time and information-searching skills.
Libraries are an invaluable source of help.
Searching Some of you will want to do the searching yourself. Whoever does the search, it is important to understand that there is a hierarchy in the published journal literature, from primary reports of research to reviews and overviews. These will aggregate the results of several or many RCTs. With aggregation many of contradictions are dissipated. The UK Cochrane Centre in Oxford has made a special study of this problem.