A growing number of marijuana users in the U.S. are experiencing severe health problems like these.As marijuana legalization spreads across the country, people are consuming more of the drug, more often and at ever-higher potencies. Most of the tens of millions of people using marijuana, for health benefits or for fun, don’t experience problems. But a growing number, mainly heavy users, have experienced addiction, psychosis and other harmful effects, The New York Times found.“Cannabis is a lot of things at once,” said Dr. Kevin Gray, a psychiatrist and specialist in bio-behavioral medicine at Medical University of South Carolina Health. “It can be medically therapeutic. It also can be highly problematic.”In interviews and surveys, hundreds of people told The Times about serious — sometimes frightening — symptoms that they were stunned to learn could be caused by cannabis. Here are some of their stories.Cannabinoid Hyperemesis Syndrome‘A Real Danger’David Krumholtz, an actor known for films like “10 Things I Hate About You” and TV shows like “Numb3rs,” resumed smoking marijuana in 2016, after a decade-long break. Within months, he started to experience cycles of intense nausea and vomiting — a sometimes debilitating condition called cannabinoid hyperemesis syndrome. It can lead to dehydration, seizures, kidney failure, cardiac arrest and even death in rare instances.He lost 100 pounds and was in and out of emergency departments. At home in New Jersey, he would spend 10 hours at a time in hot baths, which for unknown reasons can temporarily relieve symptoms.David Krumholtz said the symptoms he suffered nearly cost him his dream job.Michelle V. Agins/The New York TimesWe are having trouble retrieving the article content.Please enable JavaScript in your browser settings.Thank you for your patience while we verify access. If you are in Reader mode please exit and log into your Times account, or subscribe for all of The Times.Thank you for your patience while we verify access.Already a subscriber? Log in.Want all of The Times? Subscribe.

The drug, legal in much of the country, is widely seen as nonaddictive and safe. For some users, these assumptions are dangerously wrong.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.