Melanotan II is a synthetic peptide developed to imitate some of the actions of alpha-melanocyte-stimulating hormone (α-MSH), a naturally occurring hormone involved in skin pigmentation and several other biological processes. It interacts with a group of receptors called melanocortin receptors, which participate in functions ranging from pigment production to appetite and sexual responses. This has made Melanotan II a subject of research into skin pigmentation, melanocortin signalling, and sexual function.

Research has examined how Melanotan II influences melanin production, the natural process responsible for skin and hair colour, as well as certain responses controlled by the nervous system. Melanin is the pigment that gives skin its colour and helps absorb some ultraviolet radiation. Because Melanotan II activates several types of melanocortin receptors, researchers have also investigated effects beyond pigmentation, including changes in appetite and sexual responses.

Melanotan II has been investigated through laboratory experiments, animal studies, and small early human clinical trials. Human research has demonstrated changes in skin pigmentation and examined its effects on erectile responses in men. These studies also reported adverse effects, including nausea, fatigue, and other unwanted physical reactions, highlighting the importance of distinguishing measurable biological activity from established clinical safety.

Although Melanotan II has demonstrated activity in human studies, it is not an approved tanning treatment, and its long-term safety remains uncertain. Its effects on multiple receptor systems make it difficult to assume that activity in one area occurs without effects elsewhere. Further research would be needed to clarify its safety, longer-term consequences, and potential clinical applications.