The substance which causes epilepsy in brain tumour sufferers has been isolated, according to new research from the US's National Institutes of Health (NIH).
Scientists hope the findings will mean a substantial improvement in the quality of life of people diagnosed with gliomas, a common but deadly type of brain tumour.
The NHS says every year there are 4500 new cases of brain tumour in the UK, with many resulting in seizures.
"These seizures are often poorly controlled by epilepsy medicines," said Dr Jane Fountain, program director at NIH, who hopes new treatments will now be developed.
The results showed that a substance called glutamate, which is produced in excess by the tumour, causes an increase in electrical activity in the brain - resulting in seizures.
When sulfasalazine, an anti-inflammatory used to treat rheumatoid arthritis, was added to glioma in mice, the study saw a major reduction in the frequency of epileptic bursts over the following four hours.
Now a new trial is scheduled to determine if sulfasalazine can ultimately reduce seizures in people with slow-growing gliomas.