Reference on abuse of stimulant medications among professors to enhance academic performance?
There were several prominent publications in Nature, spurred by a survey that they conducted of their readers who were able to broadly identify their area of work.  See this link here for information about the survey, which also cites the papers that were published in Nature.  http://network.nature.com/groups/naturenewsandopinion/forum/topics/1309

In researching this topic, I used google scholar and the search terms "stress stimulants faculty -students" and published 2008 or later to arrive at meaningful search results.  

The most likely reason there is more work published on student use is that students as a demographic group are both easier to study and are a more similar group of cohorts than faculty as a demographic group, which are more diverse in age, race, ethnicity, etc.