Melanotan-II is a lab-made chemical that is similar to a hormone found in people. Be careful not to confuse melanotan-II with melatonin. Melanotan-II is given as a shot to produce erections in men with ED (erectile dysfunction), tan the skin, and prevent skin cancers caused by sun exposure. Melanotan-II is similar to a substance in our bodies, called “melanocyte-stimulating hormone,” which increases the production of skin-darkening pigments. Melanotan-II might also work in the brain to stimulate erections of the penis.