The compound has been tested successfully on cocaine-dependent rats.

Scientists are hopeful it can eventually be given to humans to decrease their desire for drugs, and to reduce the risk of relapse after withdrawal.

Currently only substitution treatments - methadone, SubutexR or nicotine patches - are available for drug misusers.

These treatments have limited impact and do not tackle the craving for drugs. Instead they simply replace one craving with another.

The new compound, known as BP 897, works by stimulating the release of the chemical dopamine in the area of the brain that governs drug dependence.

Dopamine produces a feeling of pleasure and euphoria, which helps to offset the cravings for cocaine, without producing the same addictive qualities as the drug.

However, the BP 897 only works before cocaine is taken, it does not stop cravings afterwards.

Cocaine-dependent rats

BP 897 was tested on cocaine-dependent rats trained to self-administer the drug by pressing a lever.

The rats were conditioned to respond to a light which came on at each drug intake.

They continued to press the lever when the light came on, even when no drugs were released.

When the rats were given low doses of BP 897 they became less likely to keep pressing the lever, indicating that the compound had reduced their craving for drugs.

Writing in the journal Nature, the researchers, led by Dr Pierre Sokoloff at the French National Institute for Health and Medical Research (INSERM), say that BP 897 could be used to combat other forms of dependence, for example to heroin or nicotine.

Dr Sokoloff said: "There is a very strong parallel between the animal model we used and what is observed in humans.

"Currently we have only tried cocaine but as the drug acts on the common mechanism that leads to every drug abuse we think it could also be useful in treating smoking or heroin abuse."

The researchers plan to begin trials of the drug on human volunteers in September.