WHY KICKING THE COCAINE HABIT IS SO DIFFICULT

LONDON, July 11 (Reuters) - Cocaine addicts may have such a tough time
kicking the habit because cravings for the drug increase long after they
have stopped taking it, scientists said on Wednesday.

Instead of gradually diminishing with time, an animal study showed that
longings for the popular recreational drug get worse with time and increase
the likelihood of a relapse.

The findings by scientists at the National Institute on Drug Abuse (NIDA)
in the United States could offer new insights into how to help addicts who
have repeatedly tried but failed to give up cocaine.

"This phenomenon helps explain why addiction is a chronic, relapsing
disease," Dr Alan Leshner, the director of the NIDA, said in a statement.

"Craving is a powerful force for cocaine addicts to resist, and the finding
that it persists long after last drug use must be considered in tailoring
treatment programs," he added.

NIDA scientists studied the impact of cocaine withdrawal and relapse on
rats over periods ranging from a few days to two months.

They noticed the first evidence of craving in the animals after about a
week without the drug. The longings grew over time and were the strongest
at two months, the maximum length of the study.

Dr Jeff Grimm, an experimental psychologist who led the research team, and
his colleagues said that although the research was limited to rats, it has
implications for human addiction.

"If you look at relapse rates over time you tend to see that addicts
relapse even after years of abstinence so something is persisting that is
calling people back to the drug after time," he said in a telephone interview.

"What we are seeing with the rats is that instead of immediately following
the cessation of the drug the cravings become stronger over time."

The scientists said they know the underlying mechanism which causes the
cravings but they suspect changes in the brain over time could contribute
to the phenomenon.

Grimm said the cravings in the rats were also linked to drug-associated
environmental cues, similar to what has been shown in drug addicts.

In the experiments the scientists trained the rats to press a lever to
receive intravenous cocaine injections. Afterwards they tested the animals
to determine if they would press the lever even if they no longer received
the cocaine.

Their research is published in the science journal Nature.

Drug addicts also have environmental cues, such as the sight of a syringe
or other paraphernalia, that they associate with the drug and which could
trigger a relapse.