More than 500 listings of products containing the unauthorised substance have been removed in the past two years.
Ireland's medicines watchdog's warning of "serious health risks" posed by a self-tanning substance advertised online.
The Health Products Regulatory Authority says Melanotan Two's being sold as an injectable powder, nasal spray or drops.
The HPRA says it has removed more than 500 listings of products containing the unauthorised substance in the past two years.
It's advising people who've used it not to do so again, and speak to a doctor about any health concerns.