A single snort of cocaine could be enough to get someone hooked, according to new research.
Even among recreational users the party drug triggers the 'pleasure chemical' dopamine in a brain area linked to compulsion, say scientists.
It suggests they could be further along the road to addiction than they may have realised.
Psychiatrist Professor Marco Leyton, an expert on drug use and addictions at McGill University, Montreal, said: "The study provides evidence some of the characteristic brain signals in people who have developed addictions are also present much earlier than most of us would have imagined."
The findings, published in Scientific Reports, will add to growing alarm about cocaine's long term effects.
It is Britain's second favourite illegal drug, after cannabis, and has an older user base - dubbed 'silver snorters'.
Scientists have known for many years it boosts dopamine, a neurotransmitter released during gambling, sex and addiction.
Just seeing someone using cocaine can be enough to trigger dopamine and lead to craving.
Getting the habit
As addiction progresses, it has long been suspected dopamine shifts to the dorsal striatum, a structure deep inside the brain extensively studied for its role in the way we respond to rewards.
Explained Prof Leyton: "This area of the brain is thought to be particularly important for when people start to lose control of their reward seeking behaviours.
"The dorsal part of the striatum is involved in habits - the difference, for example, between getting an ice cream because it will feel good versus being an automatic response that occurs even when it is not enjoyable or leads to consequences that you would rather avoid, such as weight gain or serious health hazards."
The findings also underscore the "importance of providing help early" to avoid the severe effects of dependency, he added.
As well as affecting the brain, cocaine poses a host of other health risks, experts say. The most significant is the strain it puts on the heart.
The drug can send the heart into spasm, making the immune system destroy healthy cardiac tissue.
It is estimated almost 750,000 adults in England and Wales use cocaine each year.
One in ten Brits have tried cocaine at least once.
Use in the UK is higher than in most other countries in Europe. And, within the UK, it's London that has the highest proportion of cocaine users.
At its peak use in 2008 cocaine was associated with 282 deaths in the UK.