Another drug being developed, which is similar to bremelanotide (PT-141), is melanotan-II (MT-II). It works by a different mechanism than Viagra/Cialis/Levitra. Here are some reports on MT-II:

First article: by Francois Guiliano, a major researcher: (LINK HERE) [Note: For some reason, the author retracted this article…not sure why.]

Second article: Also by Dr. Guiliano; you can download a pdf of the article, which is from Journal of Andrology (2004): (LINK HERE) It is pretty complicated and not for the non-medical person, but it suggests this class of drugs will be useful in the future.

Third article: This study goes back to 2000. There are some side effects with MT-II (eg, severe nausea), which may be why they haven’t developed it. (LINK HERE)