WASHINGTON (AP) — Federal health officials issued a national warning Thursday against marijuana use by adolescents and pregnant women, as more states legalize the increasingly potent drug for medicinal and recreational use.

Health and Human Services Secretary Alex Azar and Surgeon General Jerome Adams made the announcement, with Azar calling marijuana "a dangerous drug." Officials said President Donald Trump has donated $100,000 — one-quarter of his annual government salary — toward a digital campaign to raise awareness of the risks. Trump has forgone his official salary since taking office.

The warning comes as legal marijuana has grown into a $10-billion industry in the U.S. with nearly two-thirds of states legalizing it, mainly for medical uses. An increasing number of states and localities are also allowing personal, recreational use.

Countering the opioid epidemic is a top issue for the White House, but marijuana had not gotten such high-level attention.

Adams said science shows that marijuana is harmful to the developing brains of teenagers and to the human fetus. The drug has also gotten stronger, with a three-fold increase in the concentration of the active ingredient THC in cultivated plants over the last 20 years.

"This ain't your mother's marijuana," Adams said.

While many states have changed their marijuana laws, federal law still treats it as a controlled substance akin to opioids.

Federal officials say they fear the trend toward legalization may make it more enticing for teenagers to try marijuana. It's a commonly used drug among youths, they said, along with alcohol and e-cigarettes. No states allow legal marijuana use by teens.

Adams said that for teens it carries a risk of affecting brain development, which continues in the 20s. Frequent marijuana use by teenagers is associated with changes in parts of the brain that are involved with attention, memory, decision-making and motivation.

Among pregnant women, marijuana is the most commonly used illicit drug, with about 7% reporting they had used it within the past month in a 2017 study. The American College of Obstetricians and Gynecologists and the American Academy of Pediatrics advise women not to use marijuana during pregnancy, and to discontinue the drug if they find out they are pregnant.

HHS Assistant Secretary for Health Brett Giroir said pregnant women taking marijuana to relieve morning sickness should stop. "If you have morning sickness, talk to your physician," he said.