Any research is good. Medicine related research is better only if you are a huge contributor to the project. If you are more of a grunt/scut worker trying to get your feet wet in research, as long as you are involved and learning the concepts, any area of research is acceptable. Psychology research is fine.
Of course all of this depends on if you want to go to a research heavy medical school, such as Johns Hopkins, Mayo, etc.
-Senior medical student / admissions committee interviewer