Lawyers acting for more than 100 people who have suffered severe side effects which they are convinced were caused by a leading antimalarial drug have applied for legal aid to sue the manufacturers.
Sufferers have complained that the mefloquine drug Lariam, prescribed by their GPs, caused symptoms so extreme that some have been unable to work for almost a year after they finished the course of tablets.
Little hard evidence exists to link the side effects to the drug, made by the Swiss pharmaceutical giant Hoffman-La Roche, but doctors say the anecdotal evidence is overwhelming and have called for a large-scale independent study.
The company recognises that Lariam, acknowledged as the strongest and most effective antimalarial drug, can cause severe side effects which can be fatal, but argue the risks are extremely low - as few as one in 10,000.
But growing numbers of Britons who have taken Lariam - used as some strains of malaria have become resistant todrugs such as chloroquine - have reported the symptoms first highlighted in the BBC Watchdog programme.
Dr Gordon Cook, at the Hospital for Tropical Diseases in London, has seen many patients who believe it has induced seizures, epileptic fits, manic depression and panic attacks.
"I am quite clear that these problems are common and of major significance," he said. "So much so that people are not taking the Lariam and leaving themselves open to . . . malaria."
One of those who claims to have suffered and become involved in the "legal class action" is Stuart Waddell, 33, from Coventry, who has not been able to work since last April.
He took Lariam before going on a business trip to Malaysia and was affected even before he left home.
"I came over in this terrible, sweaty condition. My heart started racing and I felt nauseous . . . it took me 30 minutes to get a grip of myself," he said.
The symptoms continuedwhen he returned home. "I went to work, but only stayed for three hours," said Mr Waddell, who has four children. "I was a totally different person. I used to be self-confident, easily able to deal with pressure situations. I told my wife I thought I was going mad."
Christiane Gaoziou, the solicitor acting for the complainants, said she was confident the group would be given legal aid.
However, a spokesman for the Department of Health said any risks from Lariam were still considered extremely low.
Hoffman-La Roche said it constantly reviewed Lariam's performance but had discovered no changes in the side effects it caused.