Concerned that pregnant women and young people are becoming more likely to use marijuana, Surgeon General Jerome Adams on Thursday sounded a “national alarm” about the drug’s harmful effects on the developing brain.

Marijuana use during pregnancy can affect the fetus and may still be dangerous to the baby after birth, Adams warned in a new surgeon general’s health advisory. Teens who use the drug can have problems with attention, memory and decision making, he added.

Whether it is eaten, drunk, smoked or vaped, “no amount of marijuana use during pregnancy or adolescence is safe," Adams said at a news conference in Washington.

LIVE: Join @SecAzar and @Surgeon_General Jerome Adams for a press conference on a Surgeon General Advisory. https://t.co/2FeaeIMcGV — HHS.gov (@HHSGov) August 29, 2019

“Recent increases in access to marijuana and in its potency, along with misperceptions of its safety, endanger our most precious resource: our nation’s youth."

Among pregnant women, marijuana is the most commonly used illicit drug, he noted. Pot use in pregnancy has doubled among U.S. women, according to government research released in June. In 2016-17, about 7 percent of pregnant women said they used marijuana in the past month, compared to about 3.4 percent in 2002-03.

Some use it to ease morning sickness, but there’s no evidence cannabis is helpful in managing this condition, the American College of Obstetricians and Gynecologists said. More research is under way to seek definitive answers. The group advises pregnant women not to use marijuana, noting that substances from the drug can reach the fetus by crossing the placenta.

When THC, the chemical in marijuana that makes people high, enters the brain of the fetus from the mother’s bloodstream, it may disrupt the endocannabinoid system, which is important for a healthy pregnancy, the surgeon general’s advisory warns.

“What you’re doing by smoking marijuana is basically disturbing a very carefully orchestrated process by which the endocannabinoid system and the brain responds to stimuli and creates new connections. That’s why the concern,” Dr. Nora Volkow, director of the National Institute on Drug Abuse, said during the news conference.

Other possible risks of marijuana use during pregnancy include babies that are smaller at birth and stillbirth, the American College of Obstetricians and Gynecologists noted. Health experts have been warning about the consequences since 2015.

Among adolescents, marijuana is the third most commonly used illicit drug, behind alcohol and e-cigarettes, Adams said. That’s concerning because the human brain continues to develop into a person’s mid-20s, and frequent marijuana use during the teen years is associated with changes in brain areas involved in attention, memory, decision-making and motivation, the advisory noted.

With 33 states now having legalized marijuana in some way, Adams said he hears growing concern about the “rapid normalization” of pot use. He’s especially concerned about people using highly potent cannabis, with THC concentration in marijuana plants increasing three-fold from 1995 to 2014. That can lead to other risks, like anxiety, agitation, paranoia and psychosis.

“As I like to say, ‘This ain’t your mother’s marijuana,’” Adams said at the news conference. “The higher the THC delivery, the higher the risk.”

Marijuana remains illegal under federal law.