A growing number of people in the UK are injecting themselves with an unlicensed tanning drug, a BBC investigation has found.
Melanotan is still undergoing clinical trials but is sold illegally online and in salons and gyms, Newsbeat reports.
It is a synthetic hormone which stimulates the body's production of melanin, a substance that gives the skin its colour.
Experts are worried that the long-term effects are not yet known.
The BBC investigation found needle exchanges across the UK have noted more and more people coming in to get syringes to inject the tanning drug.
Melanotan has been developed for the treatment of skin conditions but has not yet been licensed for human use.
It is not against the law to use the drug, and Stacey Boardman, from Rochdale, said she was willing to take the risk.
It has not been tested for its effectiveness or its safety
Claire Tilstone, MHRA
"You have about 10 injections. You take an injection every day and after the 10 days you should have a nice tan," she said.
"And then if you want to go darker just carry on taking it for more than 10 days. Once you've got your initial tan, then just once a week to keep that colour you're happy with."
The government's Medicines and Healthcare products Regulatory Agency (MHRA) has written to 18 websites in the past few months warning them to stop advertising the product.
Claire Tilstone, from the MHRA, said the potential dangers were two fold.
"It has not been tested for its effectiveness or its safety," she said.
"We do not know what side effects it may cause and potentially what the long-term consequences on their health may be."
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She added there were also concerns about users injecting themselves without proper medical advice.
Melanin is produced naturally by the body. Dark-skinned people have more melanin than light-skinned people.
It also acts as a sunscreen and protects the skin from ultraviolet light.
A spokeswoman for the British Skin Foundation said: "People may think that this drug is a safe alternative to sunbeds and sunbathing because it doesn't require UV light.
"They may even think it offers sun protection, but the protection offered by a natural tan is minimal and, when it comes to an injectable, unlicensed drug, we have no idea what side-effects it may incur.
"The product hasn't yet undergone the necessary safety tests to be legally sold in this country, which should serve as a strong warning to people that it's best avoided until it is.
"There are other ways to get a tan without the risks of using an unregulated product, so until it gets the all-clear for use on humans, stick to spray tans and self-tanning lotions instead."
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