Scientists have developed a vaccine which they believe could help cocaine users kick the habit by making them immune to the effects of the drug.

The vaccine - known as TA-CD - works by generating antibodies in the bloodstream which neutralise the effects of the drug.

Cambridge-based company Cantab Pharmaceuticals has completed the first phase of clinical trials on TA-CD.

They describe the results as encouraging, and say they are now working on an anti-nicotine version of the drug which could help smokers to quit.

The vaccine was tested on 34 volunteer cocaine-users at a rehabilitation centre in New England, in the US.

The trial protocol involved three injections of vaccine at four-weekly intervals.

The tests showed the vaccine could produce the antibodies to combat cocaine with no serious side-effects.

More tests needed

The tests were headed by Dr Thomas Kosten who unveiled the findings at a conference on drug abuse in New Mexico.

"I am very keen to see this vaccine development programme move forward into more advanced trials," he said.

"TA-CD offers the potential for a new and highly viable approach to a very serious problem."

The first trials will now be followed by a second set of tests involving up to 300 volunteers, also to be held in the US.

If the second results are as promising, a third set of trials will be carried out to provide evidence to drug authorities of the safety and effectiveness of the treatment.

A spokeswoman for Cantab Pharmaceuticals said the vaccine could be on the market as early as 2004.

The nicotine vaccine - TA-NIC - is said to be a year behind the cocaine treatment.

TA-CD generates drug specific antibodies which then bind to cocaine, interfere with its transport from the bloodstream to the brain, and neutralise its psychoactive effect.

Scientists believe it could used in combination with behavioural therapy to overcome addiction.

Many cocaine misusers are treated by a specialist physician or psychiatrist in drug rehabilitation centres.

However, there is a high relapse rate associated with current therapies.