Prescription medications are becoming the nation’s drug of choice, especially among the young.

It has been four decades since the dawning of the Age of Aquarius, but aging baby boomers haven’t stopped turning on.

The federal government’s National Survey on Drug Use and Health, released in September, finds that as boomers move into their 50s in large numbers, drug use among older adults in the United States has hit its highest point ever.

Reflecting drug use in 2007, it says 1 in 20 Americans ages 50 to 59 told researchers they had used illicit drugs in the last month. More than one-half of these older users still like their street drugs, including marijuana and cocaine.

But as older users contend with the aches and pains of aging, they are adding prescription drugs to their mix, according to the report from the Substance Abuse and Mental Health Services Administration.

By contrast, the new, younger generation of drug users isn’t waiting to reach middle age to add prescription drugs to its portfolio of abuse, the report says.

Among teenagers and young adults ages 12 to 25, one-third of those who use illicit drugs say they recently have abused prescription drugs — including painkillers, tranquilizers and stimulants.

Among kids 12 to 17, 3.3 percent had abused prescription psychotherapeutic drugs in the last month. And among 17- to 25-year-olds, 6 percent had abused prescription drugs in the same period.

These generational trends are driving a significant change in the landscape of American drug abuse. After years of declining use of street drugs — cocaine, hallucinogens and marijuana — prescription medications have begun moving front and center as the nation’s drug of choice.

The result, according to the survey: Last year, Americans who began abusing prescription drugs outnumbered those who took up smoking marijuana.

Dr. Nora Volkow, director of the National Institutes of Health’s National Institute on Drug Abuse, says the report underscores a “paradigm shift” in drug abuse and, hence, in its treatment.

Though addiction to prescription drugs is not new, the current generation of teenagers and young adults has grown up around widespread medical use of prescription drugs, Volkow says, and is inclined to view them as “safe” because they are prescribed by doctors.

Because of the high from such drugs as narcotic pain relievers, she adds, young users are at high risk of becoming addicted.

Volkow adds that a shift toward prescription drug abuse also may make it harder for the new generation’s drug users to “age out” of their habit, as many baby boomers have done. Users of street drugs, Volkow says, frequently quit as they find that unpleasant side effects become more pronounced with age and prolonged use.

But users of prescription medications tend to build tolerance to the effects over time, prompting them to use more, not less, and more often, Volkow says.

Researchers with the federal substance abuse agency said they remain uncertain whether boomer drug users continued to do drugs into adulthood or, rather, returned to a youthful habit as they aged.

John P. Walters, the nation’s drug czar, expressed surprise that young Americans are turning away from cocaine and methamphetamine, but use of such street drugs continues among their elders.

Studies suggest that for the current generation, as for past generations, efforts to thwart distribution of some drugs simply shifts thrill-seekers to ones that are easier to score — a dynamic that helps explain the move toward prescriptions.Easier to get

The new report underscores the ease with which abusers of prescription drugs can get controlled substances. More than one-half of those who reported they had recently taken prescription drugs for nonmedical uses said they got the drugs from a friend or relative for free, and almost 20 percent got them from a physician.

About 1 in 10 who took prescription pain relievers said they bought or stole them from a friend or relative.

Drug-enforcement officials have long known that young people widely trade, sell and steal stimulant medications, heavily prescribed among student populations to treat attention deficit hyperactivity disorder.

Fewer than 5 percent said they had turned to a drug-dealing stranger to acquire prescription drugs.