Small ads in the back of magazines such as Private Eye, Fortean Times and the Big Issue promise payments of up to pounds 125 a day for subjects used to test the safety and efficiency of new prescription drugs. They refer to trials not only in the UK but world-wide.
The advertisers are not the clinics carrying out the trials, but companies hoping to sell people who reply a list of clinics to contact. For many respondents, the only alternative may be bar or restaurant work paying little more than pounds 3 an hour and the offers sound seductive.
The information sent out by one advertiser, Phase II Services, says: "As it is such a quick and easy way to raise a large lump sum of money in a few days, many volunteers go back time and time again, when they need money for a holiday, to see them through Christmas, to pay off loans and overdrafts or just to help them get through their next term at college."
The National Union of Students (NUS) says the danger arises less from the trials themselves, which may be perfectly legitimate, but from people anxious to earn the cash involved lying in order to take part. This is believed to be the cause of two student deaths in 1985.
"What appeared to be happening in the mid-Eighties was that people were not revealing the truth about other medication they were taking or possible risk factors to the clinical practitioners when they were taking part in tests, because they wanted the money," an NUS spokeswoman says. "We feel there shouldn't be a significant financial inducement. We really don't want people to be putting their lives at risk for the sake of money.
"We're very aware of people trying to promote this to students. I think they target anybody who wants money, and students will always fall into that category. Some companies do promote it as money for nothing."
Phase II's literature claims one volunteer recently collected pounds 5,000 plus air fare for a six-week trial in Germany. Another company selling the lists, LFC of Great Yarmouth, mentions a fee of pounds l,200 for three overnight stays.
Richard Ley of the Association of British Pharmaceutical Companies, which represents the drug manufacturers who must carry out these trials, says: "Our guidelines state that, while volunteers may be rewarded in cash or in kind, the amount should be reasonable. Payment of large amounts is discouraged, because we don't want people volunteering repeatedly for experiments for financial gain.
"Clearly, if money's being offered, it's always going to be part of the equation, but it's not something you should be doing because you're short of cash."
UK trials are policed by independent Ethical Review Boards which must approve them for safety. Trial subjects must also be told what the trial is for, what the risks might be and what compensation may be available if anything goes wrong.
One of the NUS's main concerns is trials abroad, where visitors from the UK may find any problems which arise are far more difficult to sort out. Phase II's directory lists "over 100 clinics around the world which are currently recruiting", only 15 of which are in the UK. Phase II sells its own directory for pounds 10 a copy.
Lesley Newson, director of a clinical trials unit in Plymouth, says: "We have got a couple of volunteers who got our number from one of these lists, but we don't have anything to do with the companies producing them. I don't know whether the people placing these ads are vetting the organisations, and I don't know how they choose the telephone numbers and addresses they put on their lists."
One Private Eye advertiser distributing the LFC list admits he has no idea how the list is put together, but simply sends out the list as it stands. Phase II Services bosses Nicholas Ledger and Robert Coates could not be reached.
Continuing cutbacks in state funding mean all but a tiny handful of students now have to earn some kind of outside income to support their studies. A recent survey by the GMB found that one in three students is missing lectures because of part-time work.
Mr Ley is also concerned at ads for trials being aimed particularly at groups such as students or the unemployed, who may be desperate for cash. "That doesn't mean unemployed people and students can't be accepted for trials, but companies shouldn't be targeting all their information and promotional stuff at them," he says.
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