In midcoast Maine, a pediatrician sees teenagers so dependent on cannabis that they consume it practically all day, every day — “a remarkably scary amount,” she said.

From Washington State to West Virginia, psychiatrists treat rising numbers of people whose use of the drug has brought on delusions, paranoia and other symptoms of psychosis.

And in the emergency departments of small community hospitals and large academic medical centers alike, physicians encounter patients with severe vomiting induced by the drug — a potentially devastating condition that once was rare but now, they say, is common. “Those patients look so sick,” said a doctor in Ohio, who described them “writhing around in pain.”

As marijuana legalization has accelerated across the country, doctors are contending with the effects of an explosion in the use of the drug and its intensity. A $33 billion industry has taken root, turning out an ever-expanding range of cannabis products so intoxicating they bear little resemblance to the marijuana available a generation ago. Tens of millions of Americans use the drug, for medical or recreational purposes — most of them without problems.

But with more people consuming more potent cannabis more often, a growing number, mostly chronic users, are enduring serious health consequences.

The accumulating harm is broader and more severe than previously reported. And gaps in state regulations, limited public health messaging and federal restraints on research have left many consumers, government officials and even medical practitioners in the dark about such outcomes.