Packages of a drug which users inject to create a fast tan have been seized by health and border authorities.
The so-called "Barbie drug" is claimed to make its users tanned, thin and turned on - but doctors warn it could accidentally kill someone.
The controversial Melanotan 2 is available on the internet at $68 for a 10mg vial from Australian supplier Pure Peptides.
A synthetic copy of a naturally occurring hormone, the tanning injections work by stimulating skin pigmentation over several days to create darker skin.
However, people importing the bronzing agent to New Zealand must obtain a doctor's prescription and the Australian Medical Association has told people to avoid the drug. Their board member, Dr Richard Kidd, told the Daily Telegraph newspaper that its reported side effects include nausea, flushing, darkening of freckles, high blood pressure, scarring, suppressed appetite, spontaneous erections and increased libido.
In the past year, New Zealand Customs' officials have seized parcels of the tanning drug and sent the medicines to the Health Ministry's Medsafe division.
Medsafe group manager Stewart Jessamine said 18 parcels of Melanotan were stopped at the border last year; none met the criteria for release. Prescription medicines are released to the addressee only if the person can produce a New Zealand prescription and Dr Jessamine said Melanotan 1 and 2 contain the prescription medicine afamelanotide.
Intercepted packages were usually labelled with a warning that they were for laboratory and research use only and not for human use.
The ministry said it supported the statements of overseas health authorities that there was no evidence for the drug's effectiveness and safety had not been properly tested.
"People should not be messing with something that's unproven and theoretically increases the risk of skin cancers. You might end up accidentally killing yourself," Dr Kidd told the Daily Telegraph.
The United States Food and Drug Administration has warned suppliers of Melanotan over illegal sales and their claims that it assists tanning and prevents skin cancer.
Melbourne-based global drug company Clinuvel is undertaking advanced clinical trials with tiny, under-skin implants of afamelanotide which it has branded as Scenesse.
Auckland GP and "appearance medicine" practitioner Dr Dee O'Neill undertook a trial in 2007 of Melanotan 2 with one patient who had very fair skin.
Dr O'Neill said she knew of several people, including a doctor, whose personal imports of Melanotan had been detained.
It was a promising drug, she said, but had suffered from "pirate" laboratories obtaining the formula and making and selling their own versions, and making claims they shouldn't have made, such as that it "lowers your skin cancer rate".
She wanted to see the properly-conducted trials completed.
"I do think it's got huge potential and I think once the trials are done through the proper company I hope it's on sale everywhere."
Last year, Australia's Therapeutic Goods Administration (TGA) banned Australians from buying Melanotan 2 overseas for personal use without a prescription, but news.com.au reported that two distributors of the drug had operations in Australia. One of them claimed it received more than 10,000 orders.
The TGA said: "It continues to be unlawful for Melanotan to be imported and sold [commercially]."
* Nicknamed the "Barbie drug" Melanotan 2 is injected for a fast tan.
* It stimulates skin pigmentation over several days to darken the skin.
* Its safety has not been tested and there is no evidence for the drug's effectiveness.
* Side effects include nausea, the darkening of freckles, high blood pressure, scarring and spontaneous erections.
* It costs $68 for a 10mg vial from Australia but you must have a doctor's prescription to bring it in.