Reviewer 2's Review

This manuscript is simply the best empirical report I have had the pleasure to review for a journal in my 15 years of refereeing for dozens of journals in the behavioral, social, and health sciences. I learned an enormous amount from this paper. It is very clearly written. In the introduction, the authors give an outstanding review of prior work and delineate a compelling rationale for the current studies. The authors describe comprehensive, well-designed experiments to test alternate explanations. They also provide thorough documentation of their methods and detailed presentation of their results. The discussion is balanced and includes careful consideration of other research and perspectives.

Although the importance of the subject matter is not a criterion for evaluation at PloS One, the problem addressed by the authors is important. I was initially skeptical that sugar/sweet overconsumption is an addiction, given the unprincipled and dubious extension of that term to numerous behaviors in recent years. However, I was convinced by the authorsâ?T presentation and multiple lines of evidence. This manuscript truly is a tour de force.

I have one suggestion for the authors' future research. One possible next step, if it has not been done before, is to make both cocaine and sugar/saccharin equally and freely available for continuous periods, and observe animals' preferences. This would be roughly parallel to the context for many humans. It would be interesting to see whether and how often cocaine addictions develop in such individuals under these circumstances. Another variation would be to make sugar/saccharin equally and freely available to animals that are already addicted and have regular access to cocaine. Perhaps there would be some clues in the results of such experiments that could eventually lead to potential approaches for treating cocaine abuse in humans.

N.B. These are the general comments made by the reviewer when reviewing this paper. Specific points addressed during revision of the paper are not shown.