Research is a lot like volunteer work because every medical student will have it on their application. Therefore, so should you. However, unlike volunteering, lying about research when you have not done any is more problematic. Since research is more technical than that "touchy-feely volunteer work" stuff, it is harder to pull off having done some when you really haven't. If you want to say you have done some research, it is important for you to be able to back it up with things like talking about how important your research is to all of society and dropping scientific terminology. Otherwise it is best not to mention research at all.
There are two kinds of research: clinical research and basic science research. Clinical research involves a lot of talking to patients and crunching data. It will be pretty easy for you to get a publication out of clinical research because clinical researchers will publish anything.
On the other hand, basic science research involves you spending a lot of time in a dirty old lab, doing a lot of science experiments which fail most of the time. For this reason, it is more difficult to get a publication out of basic science research. Another reason is that most professors in charge of labs are socially inept and have no desire to help you succeed. Even with all these drawbacks, medical schools like seeing basic science on applications more than clinical research because they know that clinical researchers do not actually do any work.