Bremelanotide is approved and Melanotan II is not. Same family?

Bremelanotide is an approved medicine and Melanotan II is its close relative sold online. What actually separates them?

Selectivity, mostly, and then everything that follows from being developed properly.

Melanotan II is broadly active across melanocortin receptors, which is why it produces pigmentation and arousal and appetite effects all at once. Bremelanotide came out of the same programme with a narrower receptor profile aimed at the arousal indication specifically, and then went through trials for that one thing.

So: related molecules, one of which had the unwanted activity engineered down and was then tested. The pigmentation effect people take Melanotan II for is, from the drug development point of view, the off-target activity that had to go.

And the melanoma-screening problem on the page is downstream of exactly that off-target activity.

Yes. The effect people want is the effect that makes it hard to screen them.