Cocaine can cause blood vessels in the brain to spasm or rupture, a finding that could explain why many users of the drug suffer high blood pressure, brain hemorrhages and stroke, a New York researcher reports.

In a study on rats, researcher Burton M. Altura reports he was able to produce these symptoms using "minute" doses of cocaine -- doses "even lower than what you would get in a user of cocaine."

Unlike related drugs, such as the anesthetic lidocaine, which cause blood vessels to dilate, cocaine caused them to constrict in spasms.

In larger doses, the drug caused irreversible damage to the blood vessels in the brain, Altura told a meeting of the Federation of American Societies for Experimental Biology.

Altura says the blood vessel effects may contribute to the euphoria felt by users of cocaine and other recreational drugs. But unlike with cocaine, the damage caused by other drugs "can be reversed," he says. "Cocaine is the worst."

There are an estimated 5 million to 6 million regular cocaine users in the United States, and perhaps 1 million addicts. In small doses, the drug produces euphoria; higher doses or regular use can produce a psychosis similar to paranoid schizophrenia, Altura reports.