It's dubbed the "Barbie drug" for its promise of delivering the dual perceived beauty benefits of a bronzed tan and weight loss.

If injected or used as a nasal spray, Melanotan-II can cause dramatic skin darkening as well as acting as an appetite suppressant.

However, researchers are warning about the potentially dangerous side effects of the drug that's being promoted on social media and is readily available despite being banned in Australia.

Influencers are spruiking its "wonders" and it's easy to find on websites offering home delivery.

Medical experts from UNSW Sydney are warning Melanotan-II can cause serious side effects, potentially even melanoma.

Deshan Sebaratnam, Conjoint Associate Professor at UNSW Medicine & Health says Melanotan-II is a synthetic version of a-Melanocyte-stimulating-hormone (a-MSH), which is produced in the pituitary gland of the brain.

The drug hacks the body's regulation of pigment cells, tricking the body into tanning itself.

"It means that our pigment cells produce more melanin and that's what gives you your tan," he said in a statement on Monday.

Safety concerns have surrounded the drug since it was first developed in the US in the 1990s, particularly its potential to induce melanoma, the deadliest form of skin cancer.

UNSW conjoint senior lecturer John Frew says stimulating pigment cells with Melanotan-II can cause abnormal proliferation of the cells.

"This can jumpstart the progression to the possible development of melanoma," he said.

Case reports have shown some Melanotan-II users develop skin-based complications, including melanoma, however the evidence was still limited.

Dr Frew said there were also "a few strange neurological effects" including nausea, vomiting, facial flushing as well as prolonged erections and yawning.

Melanotan-II is not approved for use in Australia by the Therapeutics Goods Administration.

Dr Frew says questions remain about how to protect social media users from the advertising of illegal and harmful products, and the responsibilities of social platforms.

"The reach of the TGA is obviously quite limited in terms of what happens on TikTok and Instagram. That's a big problem with no clear solution."