One out of every 15 high school students smokes marijuana on a near daily basis, a figure that has reached a 30-year peak even as use of alcohol, cigarettes and cocaine among teenagers continues a slow decline, according to a new government report.

Jim Wilson/The New York Times

The popularity of marijuana, which is now more prevalent among 10th graders than cigarette smoking, reflects what researchers and drug officials say is a growing perception among teenagers that habitual marijuana use carries little risk of harm. That perception, experts say, is fueled in part by wider familiarity with medicinal marijuana and greater ease in obtaining it.

Although it is difficult to track the numbers, “we’re clearly seeing an increase in teenage marijuana use that corresponds pretty clearly in time with the increase in medical marijuana use,” said Dr. Christian Thurstone, medical director of the adolescent substance abuse treatment program at Denver Health and Hospital Authority, who was not involved in the study. Medical marijuana is legal in 16 states, including Colorado, and the District of Columbia.

The long-running annual report, called the Monitoring the Future survey and financed by the National Institutes of Health, looked at more than 46,000 students nationwide. Over all, about 25 percent of 8th, 10th and 12th graders who took part in the study reported using marijuana in the past year, up from about 21 percent in 2007.

R. Gil Kerlikowske, the federal drug czar, said he believed the increasing prevalence of medicinal marijuana was a factor in the uptick. “These last couple years, the amount of attention that’s been given to medical marijuana has been huge,” he said. “And when I’ve done focus groups with high school students in states where medical marijuana is legal, they say, ‘Well, if its called medicine and it’s given to patients by caregivers, then that’s really the wrong message for us as high school students.’”

Mark Baumgartner, the director of inpatient treatment services at the Betty Ford Center, a drug and alcohol rehabilitation center in Rancho Mirage, Calif., said it was “not uncommon” for young adult patients to show up with medical marijuana cards, which can be obtained to treat conditions like chronic pain or migraines.

The report also revealed that a mixture of herbs and chemicals known widely as “spice” or “K2” — or synthetic marijuana, since it mimics the intoxicating effects of herbal marijuana — has quickly gained popularity among teenagers. One in every nine high school seniors reported using it in the past year; most of them also regularly used marijuana. In another sign of the synthetic drug’s popularity, poison control centers received 5,741 calls about it through Oct. 31 of this year, almost double the number for all of last year. This was the first year the report asked students about their use of synthetic drugs.

Part of the reason synthetic marijuana had become so popular is that until recently, it was sold legally, often as “herbal incense,” in convenience stores and gas stations and on various Web sites. But in March, the Drug Enforcement Administration declared several chemicals in synthetic marijuana Schedule I drugs, banning them for a year. Congress is now considering legislation that would ban the substance permanently.

“If you talk to school superintendents and principals, they’ll tell you about their concerns that this stuff was being sold a block away from their schools,” said Mr. Kerlikowske. “High school students probably think it’s not dangerous. But we know from the calls to hot lines, emergency departments and poison control centers that this stuff really is dangerous. It just really wasn’t on parents’ radar screens.”

While interest in marijuana and synthetic marijuana has climbed, the willingness to try most other drugs has waned. The report found declines in the use of crack, cocaine, over-the-counter cough and cold medicines, sedatives, tranquilizers and prescription drugs like Adderall and the narcotic painkiller Vicodin. Some 1.7 percent of 10th graders and 2.6 percent of 12th graders reported using cocaine in 2011, for example, far fewer than in the 1980s or ’90s. About 5 percent of 12th graders reported using ecstasy in 2011, an increase of about 1 percent from the previous year.

Heavy drinking among high school students has also fallen over the past 20 years, the report found. From 1991 to 2011, the proportion of eighth graders who reported drinking in the previous 30 days fell by about half, to 13 percent from 25 percent. Among 10th graders, it has fallen by more than a third, to 27 percent from 43 percent, and among 12th graders by about a fourth, to 40 percent from 54 percent. The percentage of students who reported binge drinking fell by a third, to 13.6 percent from 20 percent.

About a third of teenagers said they consume energy drinks like Red Bull, with use highest among younger students. Ten percent to 20 percent of high school students reported drinking one or more energy drinks daily, down slightly from 2010.

Correction: An earlier version of this post misstated the name of the federal body that in March declared several chemicals in synthetic marijuana Schedule I drugs. It is the Drug Enforcement Administration, not the Drug Enforcement Agency.