J&J has quietly succeeded in making Risperdal, unlike Clozaril, not just a schizophrenia drug. Doctors write Risperdal prescriptions for schizophrenics only about 40% of the time, while the rest are for things like behavioral disorders, mental retardation and dementia, J&J said. ''My sense is that Risperdal is like Prozac,'' a drug that is easy to use and with benign side effects, said Dr. Daniel Luchins, medical director for the Illinois Department of Mental Health. He thinks Zyprexa has similar potential.

Lilly's Zyprexa, which received an approvable letter from the Food and Drug Administration early this month, may have several things going for it. Zyprexa can be given at an effective dose right away, unlike Risperdal. Motor side effects, which are the worst results of the older drugs, are minimal with Zyprexa. Risperdal at lower doses has benign motor side effects, but at higher doses can get worse, researchers say. Zyprexa also has fewer sexual and hormonal side effects than Risperdal and causes fewer drug interactions, Lilly said. Most important, Lilly has an ongoing head-to-head study of Zyprexa vs. Risperdal, as well as studies against Clozaril. The company will make data from an interim look at the Lilly vs. J&J study available in December.

''As I go through a long list, I don't come up with a lot of reasons why Zyprexa should not be considered first-line,'' said Gary Tollofson, who heads Lilly's Zyprexa effort. But Zyprexa can cause persistent dry mouth, constipation and initial drowsiness, researchers say. Sometimes, it lowers blood pressure at the beginning of its use. Further, drugs that have clean side-effect profiles in clinical trials rarely are as clean in the real world.

Most psychiatrists said they probably will not switch patients off Risperdal. Theo Manschreck, senior psychiatrist at Massachusetts General Hospital, speculated that Zyprexa ''will be an interesting alternative to risperidone. I suspect it will be at least as commonly tried out.'' He adds, however, ''My suspicion is many patients will not be switched'' off Risperdal. Reactions like that do not reflect the expectations of some on Wall Street, where Lilly's compound has been frequently referred to as ''Clozaril without the side effects.''

And Johnson & Johnson, of course, doesn't expect to roll over. ''Olanzapine will do what it does, but we're not so sure the handicappers have it right,'' said Johnson & Johnson's Given. Cowen's Scala sees Zyprexa with sales of about $1 billion in 1999 or 2000. Estimates range from about $600 million to $1.2 billion. Some analysts expect Risperdal to have sales of more than $500 million this year. After spectacular growth this year, Risperdal is expected to grow on average in the high single digits each year for the next four years or so.

Most analysts see Abbott's Serlect as an also-ran. Abbott is not a significant marketing power and the drug appears to have some limitations. It will have to have a cap on its dose, has cardiovascular side effects and can cause things like dry ejaculation in males. Zeneca has filed its compound, branded Seroquel. Pfizer's ziprasidone is in Phase III clinical trials.