First, please note that the title you are referring to is not a part of the DrawerLayout; rather it is the title in the Action Bar.
There is no officially supported method of changing the Action Bar's title font. However, there are some workarounds in this StackOverflow question . The least hackish way to do it (and the accepted answer to the linked question) is to create your own custom Action Bar layout containing just a TextView, and setting that as so:
getActionBar().setDisplayShowTitleEnabled(false);
getActionBar().setCustomView(myCustomView);