Has medical marijuana been proven to effectively treat any medical conditions?

There are studies: But they tend to be small and focus on diseases/disease processes which involve pain, appetite issues, or muscle tone issues. If you want you can peruse the many studies at http://www.cannabis-med.org/studies/study.php. Good luck.

So far the data is: Too limited to say anything with confidence on that subject. This is my understanding. We are simply too early in the process of studying this to know that this is beneficial and that the benefits outweigh the risks. There are promising studies in cell culture and animal models, but neither of those are proof of any specific activity in Humans that compares to the cell culture and animal research