Frequent cocaine use slowly causes blood vessels to become inflamed and clotting to start, increasing the risk of a heart attack or stroke, say American researchers.
A study by Harvard University scientists showed that constant exposure to cocaine caused the body to boost production of blood-thickening factors that were normally used to slow blood loss and start tissue growth after injuries.
Cocaine use can cause problems as subtle as a nosebleed, but the symptoms can progress to cardiac arrest and death.
"Using cocaine once is like playing Russian roulette, but continued use compounds the risk so it is like adding a second bullet to the chamber of the gun," said study leader Dr Arthur Siegel of Harvard's McLean Hospital, Massachusetts.
"Instead of just the transient risk that goes away after a single usage, the regular dependent user had an inflammatory response in their system that persisted," he said.
"It means they are at a constant, ongoing risk of having a clotting event, and [levels of] the C-reactive protein that went up has shown to be associated with sudden cardiac death."
C-reactive proteins are linked to thickening in the arteries. As levels go up, they seem to overwhelm the efforts of the body's natural blood-thinners.
The result is more blood clots.
Dr Siegel and colleagues monitored the balance of these blood-thickening and blood-thinning factors by watching two groups of people.
The study involved 10 users who took cocaine between six and 20 times a week and 10 who took it between two and six times a month. All 20 users had similar levels of cholesterol.
The researchers found that levels of C-reactive protein and two other thickening components, called von Willebrand factor and fibrinogen, were higher in those who used the drug on a regular basis.
Previous studies demonstrated that cocaine use briefly caused inflammation but the new findings showed that gradual use had serious long-term impacts that increased over time.
Dr Siegel said C-reactive protein, also found in diabetics, could be measured to help cocaine users determine how severe their addiction was and to monitor their improvement as they weaned themselves off the drug.
Drugs that lowered cholesterol, called statins, could also benefit cocaine users.
"There's evidence that statins can decrease C-reactive protein," said Dr Siegel.
The study was published in the American Journal of Cardiology.
The United States Department of Health and Human Services says an estimated 1.2 million Americans used cocaine in 2000.
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