Drug has helped people quit smoking

However, those given a neutral saline solution sought out cocaine 19 times an hour.

Lead researcher Dr Edward Levin said: "It's always very exciting when a drug used for one addiction has implications for a broader range of addictive drugs."

Mecamylamine was originally used to treat high blood pressure.

Researchers now know it blocks some of nicotine's ability - and potentially that of other drugs - to generate feelings of pleasure in the brain.

Drugs like nicotine, alcohol and cocaine all increase the amounts of a chemical called dopamine in the brain known to stimulate feelings of pleasure.

Eventually, the brain may prefer the drug over natural rewards like food or sex, and hence, the person can become addicted.

Mecamylamine blocks the receptors which are stimulated by cocaine and nicotine, and thus prevents the release of dopamine.

Cocaine is able to stimulate the release of dopamine through a different pathway - but not in such high quantities.

Weakened desire

Theoretically, this means that an addict will still crave cocaine, but the desire is weakened because the brain is no longer being flooded with dopamine.

Given how few medications there are to combat serious addictions, even a medication that reduces craving can be of significant benefit

Dr Jed Rose, Nicotine Research Program, Duke University Medical Center

Dr Jed Rose, chief of the Nicotine Research Program at Duke and study co-author, said: "Mecamylamine reduces desire, but it doesn't quench it.

"Yet given how few medications there are to combat serious addictions, even a medication that reduces craving can be of significant benefit."

Mecamylamine has proven to be of significant benefit in helping people quit smoking.

In earlier Duke studies, Dr Rose demonstrated that using a patch with nicotine and mecamylamine together helped 40% of smokers quit for at least one year, while only 15% of smokers were able to do so using the patch alone.

The researchers expect mecamylamine to be approved for smoking cessation in the US later this year.