The vomiting happened with little warning and for no apparent reason.

The first episode occurred on Halloween night 2016, as Alice Moon and a friend were strolling around her neighborhood, admiring the trick-or-treaters. Suddenly Moon began to vomit. “It made no sense,” she said.

She went home and smoked some marijuana, which she knew could quell nausea and vomiting and is used by some people undergoing chemotherapy. Moon, a Los Angeles public relations specialist who promotes cannabis products, had worked in the marijuana industry since 2011. (California legalized cannabis for medical use in 1996 and for recreational purposes in 2016.)

For several years Moon, now 31, had used cannabis at night to combat long-standing insomnia and to moderate anxiety and depression. She described herself as a daily user who was not addicted. “I was never one of those people who was stoned all day,” she said.

A few days after the Halloween episode, which lasted a few hours, she saw a doctor who diagnosed reflux. He advised her to eliminate spicy or acidic foods, such as tomatoes, and to take a nonprescription acid-blocking drug.

For a few months, those measures seemed to work. But by early 2017 the vomiting returned. Moon noticed that the episodes, which occurred weekly, appeared to coincide with her consumption of alcohol, even in small amounts, so she stopped drinking.

The vomiting, however, continued. She flew about once a month for business and “lost count of how many Ubers I threw up in,” she said.

“I was definitely concerned,” Moon said, “but I didn’t know what to do.” Typically thin, she began to lose weight; at 5-foot-6, she weighed 110 pounds.

In late 2017 she read a blog item about an alarming condition affecting some regular users of cannabis: intractable and untreatable vomiting that could last for days.

“I did let it sit in my brain for a while but it didn’t make sense,” Moon said.

As the episodes increased in frequency and severity, Moon discovered that the only thing that seemed to quell hours of vomiting was a hot bath. “As soon as I’d get out of the water I would start” throwing up, she said. Some nights she fell asleep on the bathroom floor, spent and dehydrated.

One of the worst episodes occurred in March 2018 when Moon spent five days in New York City on a much-anticipated birthday celebration for her mother. Moon was overcome by waves of abdominal pain, nausea and sweating so profuse she stripped off her hat, coat and gloves despite the 30-degree temperature.

The gastroenterologist Moon saw shortly after her disastrous trip performed a physical exam and questioned her closely after Moon told her she was a regular user of cannabis.

Solution

Based on Moon’s symptoms and the relief hot baths provided, the gastroenterologist suspected cannabinoid hyperemesis syndrome (CHS), the same disorder Moon had read about — and dismissed — a few months earlier.

The unusual condition was first reported in 2004 by doctors in Australia, who described a small number of frequent cannabis users who developed severe vomiting relieved by hot showers or baths. The only way to stop the episodes, Australian researchers reported, was abstinence from marijuana.

Once thought to be rare, CHS is being reportedly increasingly by U.S. doctors in states that have legalized cannabis.

The gastroenterologist advised Moon to stop using marijuana for three to six months and return if she was still having symptoms.

Moon demurred. “I was unconvinced this was the cause,” she said. Moon decided to attend a cannabis-themed dinner party in Malibu.

A few hours after she got home, Moon began throwing up and didn’t stop for more than two weeks.

Four days into her ordeal, Moon went to an urgent-care center near her home. The doctor on duty had never heard of CHS. He administered intravenous fluids to treat severe dehydration and gave her antinausea medication, which is typically ineffective against CHS. When she seemed better, he sent her home.

Three days later, when she was still vomiting, a friend drove her back to the urgent-care center. The doctor she had seen previously called the gastroenterologist she had consulted. She ordered blood tests as well as CT and MRI scans; all were normal.

A few days later, the vomiting stopped.

For the next five months, Moon said, she mostly avoided cannabis, while struggling with insomnia and depression.

In late September, she began intermittently using CBD capsules, hoping they might be less likely to trigger vomiting than edibles or vaped marijuana. That seemed to be the case until Dec. 22 when, on a holiday visit to her family, Moon developed the worst attack she had experienced. The vomiting was so severe that Moon cut short her trip and returned to Los Angeles, where she spent four days in a hospital.

Doctors there, she said, diagnosed gastroparesis, a disease caused by the stomach’s failure to empty properly. Moon was also diagnosed with an ulcer and a bacterial infection. She said she told her hospital team about her CHS diagnosis; they told her they had never heard of it.

“People said I looked like I was dying,” remembered Moon, who slowly recovered. It was the last time she used the drug in any form.

But Moon said she did not anticipate the void that abstinence would leave, particularly because her professional and social lives revolve around cannabis. “It’s been very hard,” she said.

To Itai Danovitch, chair of the Department of Psychiatry and Behavioral Neurosciences at Cedars-Sinai Medical Center in Los Angeles, Moon’s experience reflects the difficulties many patients face. (He did not treat Moon.)

“People have strongly held ideas about substances they use,” said Danovitch, who specializes in addiction psychiatry. “There are a lot of cultural, spiritual, social and community aspects” to cannabis that strengthen users’ attachment to it.

Many people, he added, are reluctant to tell doctors that they use the drug or that they are dependent on it. CHS remains “way underrecognized” by doctors, he said, and is a diagnosis of exclusion typically made after other conditions have been ruled out.

It is not known why some users are susceptible or why hot water quells symptoms. One study found that, on average, patients racked up seven emergency room visits and three hospitalizations before being diagnosed with CHS.

Moon now uses meditation to treat her insomnia and takes medication for depression. She said she has encountered hostility from those who don’t believe CHS exists or claim she exaggerated her symptoms.

She hopes her openness about her experience will help others. Recently Moon helped the Institute for Safe Medication Practices Canada draft an informational handout for cannabis users. Her website also contains information about CHS. “I’m trying to spread the word,” she said.