Actually there are two versions of these pigmentation drugs: Melanotan-1 and melanotan II. Melanotan II is the one that has the additional arousal/libido/sexual effects.
Melanotan-1 doesn't have these effects but it does have the pigmentation effects.
Melanotan-1 (under its generic name "afamelanotide") looks set for approval for human usage as a medicine in the next year or so.
Folks can read the latest in the following two articles: