Clinical trial patients may mistakenly believe they would be compensated for accidental harm because of badly worded contracts, a senior doctor has warned.
Patients are left confused, says Professor Laurence
University of London Professor Desmond Laurence told the British Medical Journal that injury pay-out decisions were at the trial sponsor's discretion.
The government, which vets contracts, said patients are told the full risks.
There have been reports of heart problems and damage to blood cells after adverse reactions to drugs.
Prof Laurence said patients who took part in trials deserved to have the consumer contracts adequately explained to them. as they are doing society a service.
But he said documents were not written in plain language, and therefore did not meet the legal requirement of fairness and openness under consumer law.
In his letter to the BMJ, he cited the wording of the government-agreed statement: "[The sponsor] will pay compensation for [non-negligent harm]. Any payment would be without legal commitment."
He said the certainty of the first sentence was undone by the "legal jiggery-pokery" of the second.
"If the law were to be observed, patients would be told frankly, in words lay people could readily understand, that they might be seriously injured but with merely discretionary compensation.
"The trial sponsor of course may always pay ex-gratia compensation, if it cares to.
"But if it does not, then the cost of compensation for non-negligent harm falls up on the injured patients themselves."
He acknowledged that if it was spelt out clearly to people they were not entitled to compensation, the numbers volunteering for trials might drop.
But he added the answer then would be to introduce "more humane compensation arrangements".
Louise Hunt, a partner at Alexander Harris solicitors, which specialises in medical cases, said patients had a right to know what their rights were when volunteering for trials.
"The issues Prof Laurence raises are very worrying. Patients should have things fully explained to them and it is naive of the government and trial sponsors to think they do not have to do this.
"It sounds like it is very confusing for patients, I think they should be entitled to compensation."
But a Department of Health spokeswoman said: "We do not agree with Prof Laurence that patients are being misled.
"People take part in clinical trials with consent, after seeing information about the risks.
"It is a key part of the job of an ethics committee to examine carefully the information that goes to patients and others to make sure they know about the risks and the kind of compensation available before they consent to take part."