A drug used to treat patients with cystic fibrosis and heart disease could also help cocaine addicts to quit their habits.
Researchers in the United States have found that n-acetyl cysteine (NAC) can help to reduce craving in cocaine users.
The medication eliminates the 'rewards' associated with taken the drug, which keeps addicts wanting more.
This study is encouraging but we need rigorous clinical trials in humans
Dr John Marsden, Institute of Psychiatry
Tests on rats have proved so effective that human trials are now being planned.
Researchers at the Medical University of South Carolina have found that NAC has an impact on glutamate levels in the brain.
Previous studies have shown that this chemical plays a key role in cocaine dependence.
Long-term use of cocaine interferes with normal glutamate levels. If addicts stop using the drug, glutamate levels plunge.
Small amounts of cocaine can produce a large increase in this chemical, although only for a short period.
It is this surge that encourages addicts to keep seeking the drug.
But Dr David Baker and colleagues have found that NAC can help to restore glutamate levels to their normal levels.
Tests on rats have also shown that it stops the subsequent surge associated with taking cocaine.
"Treatment with n-acetyl cysteines not only restores glutamate to normal levels but also prevents glutamate levels from spiking following subsequent cocaine injections," Dr Baker said.
The tests on rats also found NAC can reduce craving.
In this study, the rats were trained to self-administer cocaine injections by pressing a lever.
When rats become used to the drug it is replaced with saline causing withdrawal. The rat usually continues to press the lever for another two weeks in the hope of obtaining cocaine.
When they stop pressing the lever, they are given an injection of cocaine. This prompts them to start pressing the lever again or craving the drug.
However, the researchers found that NAC stopped the rats from craving the drug.
NAC is routinely used to treat patients with cystic fibrosis and bronchitis.
It is also taken as a supplement by people with heart disease and is increasingly believed to help patients with HIV.
Dr John Marsden, a senior lecturer in addiction studies at the Institute of Psychiatry in London, said the findings were encouraging.
However, he added that extensive studies in humans would be needed before the medication could be administered to cocaine addicts.
"If there is a medication that would influence glutamate levels that could be really encouraging.
"There could be a potential role of this NAC agent as part of relapse prevention therapy."
Speaking to BBC News Online, he added: "This study is encouraging but we need rigorous clinical trials in humans."
The findings were presented at the American College of Neuropsychopharmacology annual meeting in San Juan, Puerto Rico.