WASHINGTON (AP) — Federal health officials are issuing a national warning against marijuana use by adolescents and pregnant women, as more states legalize some forms of the drug's use.

Health and Human Services Secretary Alex Azar and Surgeon General Jerome Adams made the announcement Thursday.

The warning comes as more than 30 states have legalized marijuana for medical purposes or personal use.

Adams says the science shows marijuana is harmful to the developing brains of teenagers and to the human fetus.

The drug has also gotten stronger. Adams says, "This ain't your mother's marijuana."

Azar said President Donald Trump is donating part of his salary to pay for a promotional campaign to highlight the warning.

The officials note that while state laws have changed legalizing marijuana, federal law hasn't.