Cannabinoid hyperemesis syndrome (CHS), a rare cyclical vomiting condition, is said to be triggered by too much cannabis. But many believe this isn’t true—and instead say the painful bouts of vomiting come from other factors, such as pesticide contamination.
Recently, the idea that neem oil (a very common pesticide) could be responsible for CHS has become a popular theory.
But is this theory plausible? While plenty of rare allergies and sensitivities to cannabis certainly exist—and some say that neem oil is the most likely cause—medical experts and CHS sufferers have concluded the theory simply doesn’t hold water. So what is the cause of CHS?
Cannabinoid Hyperemesis Syndrome Defined
Doctors first identified cannabinoid hyperemesis syndrome in 2004 when a new set of symptoms starting showing up for some cannabis users.
These patients came to emergency rooms complaining of recurrent episodes of intense nausea, vomiting for hours, and unusual body temperature shifts. Prolonged vomiting dehydrates the body, and in rare cases can lead to deathfrom kidney failure.
Strangely, for all of these patients, the symptoms could be relieved by taking hot baths or showers.
Blood toxicology showed no drugs in these patients’ systems, other than cannabis. Most sufferers used large amounts of cannabis daily—grams of extract per day, or several ounces of flower per month. So doctors suspected heavy use might play a role, and recommended stopping use entirely to see if that helped. Most of these patients stopped their use and had their symptoms subside. But those who continued using cannabis, continued to be ill.
Suddenly CHS was a thing. Even if the mechanism wasn’t fully understood, there was a clear profile of symptoms that was unlike anything else.
By 2012, more cases of CHS began to appear in the medical literature. While it is considered extremely rare, the exact numbers are hard to pinpoint. Some experts like Dr. Ethan Russo say there are only around 200 identified cases in the world. Meanwhile, there are online message boards and Facebook groups dedicated to CHS with thousands of members who believe they may have this condition.
A Neem Oil Theory of CHS Emerges
Despite the association between stopping cannabis and CHS symptoms going away, many remain unconvinced CHS can be a reaction to cannabis overuse. Some argue that the condition is actually the result of pesticide poisoning—specifically from neem oil, a pesticide commonly used by commercial and home gardeners.
Neem oil is deemed an “organic pesticide” as it comes from the vegetable oil of seed kernels from the neem tree (Azadirachta indica). Neem oil contains active ingredients like azadirachtin, nimbin, picrin, and sialin.
This theory gained prominence through CHS patients like Taeia Kaley-Dolan, who started doing her own research on the syndrome and noticed similarities between the symptoms of CHS and poisoning from azadirachtin, one of the chemicals in neem oil. Both CHS and azadirachtin poisoning can cause severe vomiting and nausea. However, azadirachtin poisonings are rare and symptoms also include not just vomiting, but seizures, acidic blood, and deadly nervous system swelling.
Kaley-Dolan shared her theory to help others with her condition understand that it might not be from cannabis, and many in the cannabis space echo the theory that CHS might really just be pesticide poisoning, or something—anything—other than cannabis.
Cannabinoid hyperemesis syndrome is sort of like the boogie man for cannabis consumers. It comes without warning and turns your ideal medicine into your worst nightmare, but it’s also rare, so many have never met someone with the condition. It’s no wonder that the cannabis community pushed back on this theory, saying it must be misdiagnosed or totally made up.
Russ Hudson, a Barcelona, Spain-based cannabis consultant who has been working in the space for 27 years agrees. “I would posit that most veterans in the cannabis industry—people with 20-plus years of experience—think that cannabis hyperemesis is a made-up or severely ‘misunderstood’ (read; misdiagnosed) condition,” he shares. Hudson says that he’s never met anyone with this condition in his entire time working in the space, and isn’t sure it’s real.
According to Hudson, “Azadirachtin poisoning seems a likely culprit, as well as other types of contamination,” such as bacteria or other pesticides. He also points to allergic reactions to terpenes or an uncomfortable reaction to being too high as potential causes.
Registered nurse Doug Rhodes is a wellness educator who has seen two cases of CHS first-hand agrees with Hudson and Kaley-Dolan, saying, “I’m a firm believer that hyperemesis syndrome is from contamination, be that neem, pyrethrum, or other products.”
So could it be that CHS isn’t a real thing? Could it be that we are just seeing pesticide poisoning and there are no cases of true CHS—cyclical vomiting actually caused by cannabinoids?
Unfortunately, this theory doesn’t line up with the evidence.
Neem Poisoning Differs From CHS
While we’d all love to hear the news that CHS could be solved by avoiding neem oil, the medical experts we talked to say this theory doesn’t make much sense. The effects of these two conditions are just too different from each other.
“As much as I decry the use of pesticides on cannabis, their toxicity profile does not match the symptom complex or time course of CHS,” explains leading cannabis researcher and neurologist Dr. Ethan Russo. “Neem oil and azadirachtin generally have limited human toxicity, but can rarely produce vomiting (the only symptom in common with CHS).”
Dr. Russo points to the other symptoms of azadirachtin overdose like increased salivation, diarrhea, liver toxicity, and convulsions. “The latter symptoms do not match CHS at all,” he says. “This is someone’s wishful thinking, or just another conspiracy theory.”
Furthermore, neem oil poisoning cannot be treated with hot showers, a core feature of CHS.
Jeff Raber, PhD, a cannabis researcher and organic chemist, agrees that neem oil isn’t likely to be the culprit.
“Someone sent the neem oil link to me a while ago and I was just like, ‘It doesn’t make that much sense,’” he recalls. “A lot of people use neem oil on that and on a lot of other products. We don’t see neem oil hyperemesis syndrome. I think we’d see a lot more cases because of the prevalence that neem has been used.”
These experts say that the CHS cases they’ve encountered and studied seemed to consistently respond to one major factor: cannabis use. They both believe that an overabundance of cannabinoids is causing nerve cell signalling dysfunction. The theory comports with what’s known about cannabis, based on cell, animal, and human trials. Take vomiting, for example. At low doses, cannabis can treat nausea. But at high doses—the opposite occurs.
“Phytocannabinoids such as THC are noted to produce biphasic effects, i.e., they may produce one effect at a low dose and an opposite effect at a much higher dose,” explains Dr. Russo. “THC is normally antiemetic, but perhaps in CHS this reverses after heavy chronic usage.”
Scientists know THC stimulates the body’s CB1 receptor—found in the brain and the gut. The body responds by decreasing the number of CB1 receptors on nerve cells. That’s how tolerance to THC develops. If the number of CB1 receptors falls below a certain threshold, boom, hyperemesis, scientists think.
Another factor is the TRPV1 receptor, also known as the capsaicin receptor or the vanilloid receptor 1. This receptor seems to be involved in CHS, and is activated by cannabinoids. Issues with TRPV1 could explain why hot baths help, since they are also known to activate that receptor.
Still, what’s not clear is why this condition affects only a small subset of cannabis consumers.
While both doctors said more research should be done to understand this rare condition and the exact mechanisms driving it, both were also convinced that pesticides could not account for the symptoms seen in CHS.
Patients Get CHS From Clean Cannabis
Perhaps the biggest nail in the coffin for the ‘CHS is just pesticide poisoning’ theory is the fact that some patients have gotten CHS from cannabis that was grown without pesticides, including neem oil.
Take Jared Panks for example. The 39 year-old is a co-owner for Home Grown ORegonicX, a company in Oregon that teaches deaf individuals how to cultivate cannabis. He sources cannabis from his own organic garden, which is pesticide-free (including neem). So when he was diagnosed with CHS, he knew that pesticides couldn’t be the reason.
“I have all this documentation with all the genetics that I’ve grown, all the mold tests, all the pesticide tests, all that stuff, and I’m still getting sick,” he explains.
Panks’ symptoms line up perfectly with classic CHS—cyclical vomiting that increases with more cannabis use, and is relieved by hot baths and cannabis cessation. Panks’ worst attack left him unable to hold down food or water for 14 days. He needed to be hooked up to IV’s to survive the severe dehydration.
“For me, I think it’s an overload on cannabinoids,” he explains, adding that he’s tried cannabinoids other than THC, like CBD and CBN, and still had bad reactions. The only thing that has helped is lessening his intake of cannabinoids. “They can’t clinically say that anybody’s ever overdosed from it,” he adds. “I can say that I’ve overloaded. And that’s the truth.”
Alice Moon, a 29 year-old from Los Angeles with CHS, says she is also convinced that pesticides are not the problem. She put her body through the ringer hoping that pesticides might be.
The cannabis public relations person was once a cannabis edible reviewer, but had to shift her career focus when she discovered her recurrent vomiting would only stop when she ceased cannabis use. After quitting, her symptoms subsided and Moon decided to try again.
“I started smoking pesticide-free weed because so many people say CHS is pesticides,” she explains. “But I smoked pesticide-free weed and my symptoms came back after a few months.”
Her last attempt was to use hemp-derived CBD from a source she knew used no pesticides including neem. But one day, a larger than normal CBD dose sent her back to the hospital with her worst CHS bout yet—16 days of non-stop vomiting.
“I had so many moments where I was wondering if I was going to die because it was so severe,” she recalls. By the end of her stay she had three ulcers, a hernia, and a bacterial infection from the experience.
“Now, I will not be a guinea pig at all,” she explains. “I can’t do it. My body can’t do it.”
Since her own failed experiments getting rid of CHS without stopping cannabis, Moon has been outspoken about CHS and her belief that it is truly related to cannabinoid intake. “I 1,000% believe it’s not neem,” she says, adding that she even had a blood test that came back negative for any pesticides.
“I do believe people can have pesticide poisoning. I am not denying that that’s real,” Moon says. “But I do think that this isn’t that.”
Moon says that since going public with her thoughts on CHS, she’s gotten a lot of negative responses from the cannabis community.
“I get so much online hate in regards to this,” she explains. “Every other day, people are telling me, ‘You made this up. You work for the government. You work for Big Pharma.’ I’m like, ‘No dude, I just want to be able to smoke weed again.’”
Moon says she believes in the medical benefits of cannabis but wants to educate people about CHS so they’ll stop as soon as they exhibit symptoms and not risk their lives thinking pesticide-free cannabis will help. But Moon says, “People don’t want to believe it’s real.”
“You can have too much water,” she points out simply “So why are we trying to pretend that you can’t have too much cannabis?”
Are Sub-Populations Sensitive to Pesticides?
While the bulk of CHS sufferers must reduce their cannabis intake to be cured, some rare sub-groups most certainly have CHS-like symptoms related to cannabis’ many added ingredients. One such person is Leafly’s own Natalie Bernstein, a performance improvement analyst.
Bernstein moved to Washington in 2014 to use cannabis to manage her chronic migraines. In the spring of 2017, she switched from a pesticide-free, illicit market source of cannabis to store-bought cannabis. By summer of 2017, she developed what she thought might be CHS—nausea and intense vomiting following cannabis use.
While she worried she had CHS, her symptoms didn’t line up. She wasn’t a heavy smoker. And hot showers didn’t stop the vomiting. Rather, the antihistamine Benadryl controlled her nausea, she discovered by accident.
Bernstein has many allergies, and new ones can pop up seemingly out of nowhere. Suspecting a rare type of cannabis contaminant allergy, Bernstein started tracking her intake. To source neem-free cannabis, she used Washington state’s cannabis industry pesticide application data, and called growers directly.
She found a strong correlation between inhaling flowers treated with neem oil, and her nausea and vomiting. “My doctor told me that I was wrong, that it was THC, so I stopped seeing that doctor,” she said. “People say neem is ‘organic,’ but poison ivy is organic.”
By winter of 2017, she determined she could control her nausea through edibles, or inhaling neem-free cannabis.
Bernstein believes not all CHS cases are caused by heavy cannabis use. There’s probably a spectrum of CHS causes, where maybe 70% of CHS sufferers might have classic CHS, she believes, while maybe 20% have a reaction to pesticide toxicity, and 10% have rare allergies to even trace amounts of pesticides, like her.
“It’s really difficult to say that any one answer is going to apply to everybody,” Bernstein said. “I think what I have is more prevalent that what people know.”
Neem Oil Generally Not Causing CHS
So is neem oil the cause of CHS? Generally not. The bulk of early evidence points to overactivation of the CB1 receptor. The old adage “moderation in all things” holds true.
There is a long way to go in understanding CHS, and why it only affects a segment of heavy cannabis consumers. More research is needed to fully understand what factors are at play in this mysterious condition.
Still, while we’d all love to hear that CHS is just a made up condition or a misdiagnosis of something we can easily fix, the pesticide theory doesn’t match most case studies. Patients like Moon and Panks are suffering from a very real condition, one that can’t be explained by pesticides.
When pesticides are taken out of the equation, CHS remains.