The "Barbie drug" is back

• It can be found as a nasal spray or shot, but it's not approved by the FDA or any other major regulator.
• Case studies suggest it could lead to the development of skin cancer.

What we're hearing: "People who inject melanotan, their moles start to change," says Anthony Rossi, a dermatologic surgeon at Memorial Sloan Kettering Cancer Center. He's removed atypical moles from a patient who used it.

• But he's seeing it taken at the gym as part of a "beautification stack" — and he's worried.
• "I don't really see a medical benefit of it at all," Rossi says.