· Rise in availability of unproven drugs online causes increasing concern as patients go online to buy dodgy drugs that may poison or kill rather than cure.

A colour enhanced scanning electron micrograph (SEM) of a breast cancer cell. Photograph: Science photo library

The government was yesterday warned that cancer sufferers are at increased risk from websites selling unproven cures that could wreck the remaining months of their life. The controversy centres on a drug called DCA (dichloroacetate), a chemical being promoted and hyped across the world as a cure for cancer after news of preliminary laboratory tests on rats.

Dr Ian Gibson, chairman of the all-party parliamentary group on cancer, warned that increasing numbers of British people were purchasing such products, and urged the government to do all it could to highlight the problem and block sales from the websites. The proliferation of such sites was "an increasing problem which started in the United States and is growing almost daily here," he said.

DCA is a cheap off-patent chemical which was the subject of various largely unpromising trials for different diseases dating back around 20 years. It came back to prominence after research on early animal laboratory work by two scientists in Canada was published in the Cancer Cell journal in January last year.

The research by Dr Evangelos Michelakis and his colleague Dr Sebastian Bonnet showed regression of several types of cancer tumour, including brain, breast and lung, with no effect on healthy tissue. Their theory is that DCA restores the mitochondrial function, responsible for energy production, in cells damaged by cancers, allowing them to self-destruct and decreasing tumour growth. If they are right, they may have hit on a new approach to cancer treatment.

Subsequently, Jim Tassano, who runs a pest-control business in California, began to manufacture and sell DCA to all-comers on a website. The US authorities have attempted to stop a California-based website selling the drug, but the Guardian was easily able to obtain a tub of the powdered chemical, with a recommendation to try it with caffeine from strong tea and coffee. Tassano says he only wants to help people who have run out of options.

One of the scientists researching DCA's effect on cancerous cells is appalled. "The concern about this drug is that at this stage it is given to people who are very sick. Unsupervised, it could kill you," said Dr Michelakis, a professor at the University of Alberta who carried out tests in animal brain, lung and breast tumours and is now moving into human trials.

Tassano said in an email to the Guardian: "I am reluctant to speak publicly due to FDA [Food and Drug Administration] issues ... They have made it clear that they do not like high profile people. I am in a tough spot running both the information site on DCA and being involved with it economically as well. If the FDA takes action against me, it will be a big setback for DCA and cancer patients. I hope you understand."

The sale of DCA underscores how difficult it is for authorities to stop people purchasing potentially dangerous drugs on the internet. Gibson said he was very concerned that patients were being given false advice and erroneous information about drugs that had not been tested on humans. "I'm calling for these websites to be researched by the Department of Health and closed down instantly.

"We need to start a campaign to get the message out there that these sites are no good. If need be, we should be talking to the cancer institutes and charities in America to see what pressure they can bring to have the sites closed. But it's a very difficult thing to do. People will always turn to sites like these when they are desperate, so we need to make sure they know the facts."

Michelakis is moving as fast as he can into human clinical trials that will start to give some real answers. "The people who decide to sell this are like drug dealers. They are targeting the most vulnerable people you can imagine," he said.

Tassano and others believe those with terminal cancer should be allowed to take what risks they choose. Most doctors think patients should take calculated risks only within clinical trials, where they can be properly looked after if things go wrong.

Two doctors in Canada have broken ranks. Akhbar Khan, a GP, and his wife Humaira Khan, whose background is in public health, offer DCA at their Toronto clinic. They have been criticised by other doctors and regulatory bodies, but are allowed to use the drug because, although DCA is not approved as a cancer treatment, it is licensed for metabolic diseases.

Most of their patients are from Canada and the US, but some have made the trip from the UK.

"We haven't seen it cure anyone. It has prolonged life and given a better quality of life," said Dr Humaira Khan. "There's also the psychological aspect: the family feels they are doing something."

The couple are adding other unproven drugs to their repertoire as they hear about them. "The patients out there are researching like crazy and finding all sorts of things on the internet. They bring me lots of literature," said Dr Akhbar Khan.

On the basis of a few patients who said they had positive results from DCA and drank a lot of black tea and coffee, Tassano suggested that people try "the caffeine protocol". Yet he now warns on the site that the idea has resulted in death for some patients. "We are seeing very severe responses to the DCA-caffeine protocol in brain cancer patients. We have heard reports of a couple of people who were on high doses of DCA that started drinking caffeine and had very severe reactions: seizures and death followed," he said.

Dr Kat Arney of Cancer Research UK said the scenario around DCA was "probably the worst thing possible". "Cancer patients are taking this drug with no idea if it is safe, or at what dosage. It could make them very ill indeed."

The Department of Health said responsibility for websites selling medicines rested with the Medicines and Healthcare Regulatory Authority (MHRA). The MHRA in a statement said websites operating illegally in the UK had been closed down and said it was making efforts to alert consumers to the dangers of buying any medicines through the web.

Published with kind permission of The Guardian newspaper.This article appeared in the Guardian on Monday April 28 2008 on p1 of the Top stories section. It was last updated at 11:32 on April 28 2008.