By Kim Baldonado
(KNBC/NBC) - An increasingly popular tanning supplement is raising concerns among doctors.
Melanotan is an injection sold only online.
Its makers claim it creates a tan that lasts for months and boosts libido.
The substance has been banned in Australia and is not approved for use in the United States, but is still available.
Dermatologist Dr. Lisa Benest says the injection stimulates pigment cells, but could also stimulate the same cells that turn cancerous.
"The studies are not long-term enough," she warns.