Many young Americans live, work or play beneath a mushrooming cloud of marijuana smoke: Almost one out of five Americans say they've tried it: about one out of every 14 regularly smoke it.

The country's taste for other mood changing drugs is considerable. Millions alter their moods with amphetamines or related stimulants like Benzedrine or "bennies," once widely used as appetite suppressants in weight control programs. The "uppers" carry "street" names spawned by their subculture, evoking images as colorful as their rainbow hues: "copilots," "speeds," "crank," and the like.

But nicknames don't begin to describe the dangers of use, warn medical experts.

Still, millions choose to ignore the warnings, and relieve their anxieties with minor tranquilizers like Librium and Valium, or sedate their troubles with more powerful sedative phenobarbital or "purple hearts," Quaaludes or "ludes," and a host of other socalled "downers" with nicknames like "reds," "yellow jackets," "blues" and "rainbows."

Six million regularly slip into a dreamlike state of confusion and disoreintation through the deadly PCP or "angel dust," according to government figures. And a small, growing number of upper middle class young professional often gather at chic parties to "snort" thin lines of the white powder up their nsotrils: cocaine.

Sociologists, psychologists and other experts says such trends are troublesome and worry about the millions who spend their days flying high. The country's 93 million drinkers and 65 million tobacco smokers are using drugs, too, even though their use is within the law.

To the extent that use of drugs overlaps, authorities aren't sure how many people are involved. What they are certain about, though, is that millions more are taking pills from their medicine cabinet on doctors' orders and gobbling them at an astonishing rate.

The lines between drug use and misuse are blurry, and according to a February report of medical experts impaneled by the President's Commission on Mental Health, the "overwhelming majrity" of "psychoactive," or "mind-altering" drug users are classified as "experimental, recreational or circumstantial" and don't threaten themselves or others.

That is not to say that dabbling with drugs for "fun" or "recreation" is rsk-free. Emergency rooms still treat many cases of drug overdose, and the number of car smash-ups, and other accidental injury and deaths caused by drugs is impossible to determine.

When it comes to $100-a-gram cocaine - an amount, it is said, that two people can easily use in an evening - the high cost of getting high appears to rapidly cut into indulgence.

The widespread use of marijuana and, to a lesser extent, cocaine, has put America on the map of a cultural phenomenon whose roots go back to 2525 B.C. and ancient China, where doctors prescribed cannabis or marijuana medicine.

When it reached 19th century England, Queen Victoria is said to have used it to relieve the pain of menstrual cramps. A significant influx of the weed crossed the Mexican border into the U.S. with migrant workers around 1900, and three decades later the government tried to warn the country against its use with movies like "Reefer Madness." College students in the '60s adopted "grass" as their drug of protest and pleasure, and it use skyrocketed along with the Age of Aquarius.

It was not until the 1960s, says Dr. Lester Grinspoon, associate professor of psychiatry at Harvard Medical School and a cocaine expert, that cocaine was adopted as the "champagne of illicit drugs."