An annual survey on drug use found increases in dagga use among all age groups but showed slightly fewer high school seniors were smoking than in recent years.
"These high rates of dagga use during the teen and pre-teen years, when the brain continues to develop, place our young people at particular risk," National Institute for Drug Abuse director Dr Nora Volkow said in a statement.
"Not only does dagga affect learning, judgment, and motor skills, but research tells us that about one in six people who start using it as adolescents become addicted."
The survey of 46,482 students from 396 schools found that 16% of eighth-graders, typically 13 and 14 years old, admitted to using dagga, up from 14.5% in 2009.
More than 21% of high school seniors, aged 17 and 18, said they had used dagga in the past 30 days, while 19.2% said they smoked cigarettes. This is the first time dagga use has passed cigarette use in the survey.
The survey found binge drinking, defined as having five drinks or more in a row, was down. Just over 23% of high school seniors admitted to binge drinking in the past two weeks, compared to 25% in 2009 and 31.5% in 1998.
The survey found more than 6% of high school seniors use dagga every day, up from 5% last year. More than 3% of 10th graders and 1% of eighth graders said they used dagga daily, all increases over 2009.
Federal officials were most upset by the dagga data and said teens may be confused about whether dagga is safe and acceptable because several states have recently legalised the use of dagga with a doctor's prescription.
"Mixed messages about drug legalisation, particularly dagga, may be to blame. Such messages certainly don't help parents who are trying to prevent kids from using drugs," said Gil Kerlikowske, director of the White House Office of National Drug Control Policy.
"We should examine the extent to which the debate over medical dagga and dagga legalisation for adults is affecting teens' perceptions of risk," Dr Volkow added.
One group advocating for legalising dagga agreed.
"Our government has spent decades refusing to regulate dagga in order to keep it out of the hands of drug dealers who aren't required to check customer ID and have no qualms about selling dagga to young people," said Rob Kampia, executive director of the dagga Policy Project.
The survey also found more teens are using MDMA, or Ecstasy. More than 2% of eighth-graders said they had tried it, compared with 1% in 2009, while 4.7% of 10th graders reported using it, up a full percentage point. (Reuters Health/December 2010)