BBC headline : Drugs trial men 'seriously ill'
The healthy volunteers had been given an anti-inflammatory drug at a private research unit based at Northwick Park Hospital when they suffered a reaction.
Myfanwy Marshall told BBC News her boyfriend's body was badly swollen and his organs were failing.
An investigation has begun at the unit, run by Parexel, which said it followed recommended guidelines in its trial. < !-- E SF -->>
ng men were being paid to take part in the early stages of a trial for the drug TGN1412 which is designed to treat conditions such as rheumatoid arthritis and leukaemia.
But within hours of taking it on Monday, six volunteers had to be admitted to intensive care - a further two had been given a placebo.
Northwick Park Hospital's intensive care director Ganesh Suntharalingam said two were in a critical condition, and the other four were serious but showing some signs of improvement.
He added his team had been doing everything possible in this "unique set of circumstances".
"The drug, which is untested and therefore unused by doctors, has caused an inflammatory response which affects some organs of the body," he said.
Ms Marshall, 35, whose boyfriend is critically ill, said the normally healthy 28-year-old barman's face was so puffed, he "looks like the Elephant Man".
She said: "His friends cannot even face seeing him. I have to stay there because I'm looking beyond all the wires and the puffiness.
"This is not leukaemia, this is not pneumonia, this is not something they know how to deal with."
The Medicines and Healthcare products Regulatory Agency (MHRA) immediately withdrew authorisation for the trial and an international warning was sent out to prevent the drug from being tested abroad.
MHRA inspectors have visited the independent research unit and are in talks with the local strategic health authority, the Department of Health and police about the cases.
Its chief executive Professor Kent Woods said: "Our immediate priority has been to ensure that no further patients are harmed.
"We will now undertake an exhaustive investigation to determine the cause and ensure all appropriate actions are taken."
It had approved the trial and the drug had already been tested on animals.
Volunteers are paid up to £150 a day to take part in clinical trials.
Parexel, which was running the trial, said it had followed guidelines and such cases were extremely rare.
The Medical Research Council said that while it was "an unfortunate and extremely rare event", such clinical trials were essential for the development of new and better treatments.
Professor Herman Scholtz, from Parexel, said: "When the adverse drug reaction occurred, the Parexel clinical pharmacology medical team responded swiftly to stop the study procedures immediately.
"Such an adverse drug reaction occurs extremely rarely and this is an unfortunate and unusual situation. We did everything possible to get the patients treated as quickly as possible."
TeGenero, the Germany-based manufacturers of the drug, said the events were completely unexpected and did not reflect results from initial laboratory studies.
Health secretary Patricia Hewitt said: "It is a shocking event and obviously our thoughts are with those young people and with their families."