Smoking crack cocaine can cause strokes even in young, apparently healthy people, according to a new study. The symptoms usually begin while the user is smoking crack or within the next hour.

The study of 28 patients who suffered strokes and brain hemorrhages after using the drug provides new details on a catastrophic complication of cocaine use that is becoming increasingly frequent with the growth of the crack epidemic.

The report is being published in Thursday's issue of the New England Journal of Medicine. The normal Thursday embargo on releasing the findings was broken by the Reuter news agency.

Most of the patients in the study were black men, with an average age of 34. Most did not have identifiable risk factors that would have heightened their chances of a stroke. Patients were enrolled in the study by neurologists at Detroit's Henry Ford Hospital, New York's Harlem Hospital Center, the University of Miami School of Medicine and Yale University School of Medicine.

The researchers found that, for unknown reasons, alkaloidal cocaine, or crack, seems to affect the brain somewhat differently from cocaine hydrochloride, the kind that is usually inhaled or "snorted." The latter type, whose use long predated the appearance of crack in the early 1980s, has been associated with brain hemorrhages.

In contrast, the new study showed that in almost two-thirds of the crack users who had strokes, sudden blockage of a blood vessel in the brain was the cause. In the rest, the strokes were caused by hemorrhages that damaged brain tissue.

Sixty-four percent of the patients developed symptoms -- such as severe headache, seizures, loss of vision, weakness or trouble speaking -- while they were smoking the drug or within an hour after smoking. In a few patients, stroke symptoms first appeared as long as two or three days after using the drug.

The study could not identify a consistent pattern of factors that would place a crack user at especially high risk. Ten patients had recently smoked tobacco, and four had a history of high blood pressure -- known risk factors for stroke. Several patients had recently used alcohol, heroin, codeine or other drugs.

The study said crack may cause strokes more than one way. For instance, a sudden, steep rise in blood pressure produced by the drug could provoke a hemorrhage, and heart-rhythm abnormalities induced by cocaine could dislodge a clot inside the heart and send it to the brain.