A researcher whose widely publicized study concluded that cocaine was a nonaddictive, safe recreational drug has reversed himself, saying half of cocaine users run the risk of becoming dependent on the drug, which he now considers potentially lethal.

"If people knew what the experts know," Ronald K. Siegel said, "they wouldn't go near this drug." Siegel, of UCLA's Department of Psychiatry and Biobehavioral Sciences, published his earlier findings in a 1977 National Institute on Drug Abuse report. He now has contributed to an institute report that, translated into 1960s street language, says: Coke kills.

"It is really difficult to wave a lot of red flags about cocaine," Siegel said in an interview. "You can't tell people it kills brain cells; that's not correct . . . . But in 1977 there were no signs of physical dependence. Now we have evidence of both increased tolerance and withdrawal symptoms. It can no longer be considered the safe recreational drug users thought it to be in the '70s. There is a lot more liability for toxicity and dependency than we had previously thought."

In early stages of the study, Siegel said, "we did not find any serious physical or psychological problems." Over nine years, however, "We found that 50 percent remained social users, but the remaining 50 percent escalated their use and had increasing physical and psychological problems."

He said, "If you are a social user, you have about a 50 percent chance of controlling it, and what category you will fall into can't be predicted. It's a very risky game to play."

Siegel said he does not like the term "addict" and spoke instead of "five patterns of escalated use":

* Experimental -- trying the drug.

* Social and recreational -- shared use in social settings.

* Circumstantial -- used in an attempt to enhance productivity.

* Intensified -- daily or almost daily use.

* Compulsive -- uncontrolled, escalating use until the body or the drug supply is exhausted.

"Patterns and dosages define the problem," Siegel said.

"People are doing it differently and they're doing it more, and it's led to a new array of problems, the most serious of which come from smoking cocaine."

Users who develop a tolerance for cocaine can increase their use only to find that "they can't quite recapture the initial euphoria. And they end up compulsive users," Siegel said. "People who are free basing and intravenous users are at the highest risk, although we're now starting to see compulsive intranasal use."

Siegel says there is no way to predict how a body will react to cocaine over time: "Tremendous tolerance builds up. I've seen people inject 1 1/2 grams of pure cocaine and survive it. Theoretically, these people should be dead."

He cautions, "There's also something called reverse tolerance where, over a period of time, the user becomes sensitized and can die from just one hit . . . . I have to be honest with the data: Most people will not fall into this dramatic population and die or go crazy or kill each other or have seizures . . . . [but] sure, cocaine kills."