Teenagers have gotten the message about tobacco, but their attitudes about the dangers of marijuana have softened considerably, according to an annual survey by the National Institute of Drug Abuse (NIDA).

For the first time since the Monitoring the Future survey began nearly 40 years ago, the majority of high school seniors — 60 percent — do not see regular marijuana use as harmful. In the past two decades, the percentage of seniors who have reported smoking marijuana every day has risen from 2.4 to 6.5 percent.

“In the following couple of years, this surely means we can anticipate an increase in marijuana use. That certainly is worrisome. Adolescents with their brains being developed and behaviors being shaped don’t need drugs to be part of the mix, including marijuana,” said Dr. Wilson Compton, NIDA deputy director.

Conversely, cigarette use among teenagers is at an all-time low, this year’s survey found. Fewer than 10 percent of eighth-, 10th- and 12th-graders reported smoking cigarettes in the past 30 days. The survey, done in the first half of this year, polled 42,000 students in 390 public and private schools.

Twenty years ago, 24.7 percent of teens in the same grades reported smoking at least once in the time period.

“We’ve seen a long-term drop in cigarette use, and that is really good news because tobacco is the leading preventable cause of death in the United States, with 450,000 premature deaths every year from tobacco-related illnesses,” Compton said.

“We think it’s more than messaging. As best as we can tell, lower rates of smokers are related to several factors; the No. 1 is that people no longer approve of smoking tobacco, and that is a very powerful way to shape behavior.”

It also showed drops in teen use of alcohol, prescription pain pills like Vicodin and OxyContin, and record-low usage of inhalants. But the use of prescription stimulants like Ritalin and Adderall, used to treat hyperactivity, shows troubling rises. And the number of high school seniors using hookahs — water pipes used to vaporize and inhale tobacco — rose 3 percent over 2012 results to 21.4 percent, wiping out some of the gains over tobacco.

The survey is the largest study of drug use in the nation. NIDA has been collecting results from high school seniors since 1975. It added eighth- and 10th-graders in 1991. It is one of the best predictors of adults’ future drug use.

It does not ask about methamphetamine use or the use of e-cigarettes. It also does not ask when students are using drugs or alcohol; that factor can hide influencing behavior. Researchers are particularly interested in knowing if e-cigarettes are being used by people trying to stop smoking or if they are an alternative to smoking in airports and other places where tobacco is not acceptable.

Doctors are worried about softening attitudes toward marijuana use. Last year, 56 percent of high school seniors said regular use was OK.

“When we have candid discussions about marijuana at the dinner table, our teenage children don’t seem to find it as inappropriate,” said Dr. Manoj Jain, a physician. “This is something which would have never happened when I was a teenager.”

Researchers suggest medical legalization in 20 states, plus the District of Columbia, and legalization for general use in Colorado and Washington might be eroding the taboo.

“I suspect that having marijuana approved for so-called medical purposes might give a false impression of its safety for even nonmedical use,” Compton said. “We have seen the same thing with prescription drugs. There is a reason you need a prescription.”

The Centers for Disease Control collects data on the risky behaviors among high school students every two years.