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It was clear what was wrong with Michael Verbora’s patient.

He smoked about a gram of cannabis a day (the equivalent of two pre-rolls), which helped with insomnia, anxiety and pain.

But while it eased some problems, it created others.

“He had chronic nausea and vomiting, classic cannabinoid hyperemesis, where they show up in the emergency room and have to take hot showers,” says Verbora, a Toronto-based doctor who practices cannabis medicine.

The first step in curing cannabinoid hyperemesis syndrome is to stop consuming. But Verbora’s patient, after a break, switched from grey-market to legal cannabis and started smoking about as much as before. The nausea never came back.

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Verbora says it’s the second patient of his for whom a switch to legal weed has worked.

“We know that the (Ontario Cannabis Store, the patient’s new source) has licenced producer cannabis which is regulated. We know that there’s no heavy metals, pesticides, fungus, pesticides. That’s really the only difference that I know of — that there are regulations in effect on medical and adult-use legal cannabis versus the black market, where there’s no regulation.

“I also have seen cases where it came from regulated products. I’m just really scratching my head a lot.”

READ MORE: Mysterious syndrome torments some heavy pot smokers with constant nausea

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“The pain sometimes was so bad that I couldn’t get out of bed,” says Tobias Zhuang, a 29-year-old Vancouver man who suffered from CHS for years. “Then I would finally drag myself to the ER and spend a night there hooked on IVs, getting fed painkillers, just vomiting the whole time.”

“There were days where I literally went all day puking, to the point where there’s nothing and I would eventually start puking blood. It got scary after a while.” Tweet This

Before he quit, Zhuang was smoking up to eight joints a day. He didn’t connect his health problems to cannabis, and doctors didn’t suggest a connection either.

He says he largely didn’t mention his cannabis consumption at the hospital: “I didn’t want them to suddenly look down upon me,” he says. On top of that, it’s self-inflicted. Which it was – I won’t lie. It was totally self-inflicted. But it was mostly because of the fact that it was illegal.”

In a textbook symptom of CHS, Zhuang found relief in the shower.

“We would go through tanks of hot showers,” he says “I would sometimes be in the shower for hours, praying that the water does not run out. But obviously eventually it does.”

“Hot pads were a life saver. When you have no hot water, hot pads are the next best thing.”

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Courtney Head, a 31-year-old Fort McMurray, Alta. woman, remembers similar compulsions.

“I would have a craving to be in hot water. Every time I would throw up, I would get in a hot shower, to the point where it was basically burning and drying out my skin.” Tweet This

For Zhuang, Googling his symptoms led Zhuang to one of several Facebook groups for CHS, and a cure through quitting heavy use.

“I have smoked since I’ve (quit), and it hasn’t affected me yet, but I know if I continue in my old pattern and just keep smoking every day, it will hit me and I will return back to my old self, being hyperemetic and sick.”

WATCH: Heavy pot smokers at risk of getting cannabinoid hyperemesis syndrome

CHS isn’t well-understood. One debate has to do with whether it’s caused by THC (the main psychoactive chemical in cannabis) or by some other chemical that’s present.

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“Some of the evidence tends to lend itself to THC ingredients, and that’s the predominant, prevailing hypothesis, but at the same time I have cases like this that cause me to question whether there’s a pesticide involved, or the neem oil that’s sometimes found in products,” Verbora says.

“I don’t have a clear answer yet.”

CHS is sometimes blamed on neem oil, an organic pesticide.

“A lot of people have speculated that (the cause is) a compound called azadirachtin, which is the active component of neem oil,” says B.C.-based cannabis breeder Ryan Lee.

“It’s not used in the legal system in Canada. Because it’s organic, the hippies say, ‘It must be safe to use in our practices,’ thinking that anything organic is inherently safe, which is obviously foolish.”

Neem oil can cause poisoning. It has some of the symptoms of CHS, but not all of them, Kamloops, B.C. doctor Ian Mitchell points out.

“There are some very characteristic things about cannabinoid hyperemesis — the whole hot shower thing, where people get relief. We’ve never associated that with neem oil poisoning.”

Are heavy smokers more affected because they’re consuming more THC, or whether they’re consuming more of another chemical?

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“As your consumption goes up, your consumption of toxins, heavy metals and all that would also go up. Your exposure to smoke would also increase,” Verbora says.

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One problem in studying CHS is that until legalization, it’s been very difficult for doctors to learn anything about the specific cannabis that was causing the problem. Under prohibition, patients may not have known anything about how their cannabis was produced, or by whom — or if they did, they might not have been willing to talk about it.

“I think it would be great if we could cross-reference these cannabinoid hyperemesis syndromes to specific products in the batch,” Verbora says.

“If there’s a problem in the future with legal products, then we can look back and start to dig deeper into the specifics of it.”

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For Lee, the evidence is consistent with CHS being caused by excessive amounts of THC, not some other chemical.

“Legal products are also typically low-potency. The problem with this whole thing is that it’s not a controlled experiment. When you switch source, you could also be switching source on the potency of the product.”

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Reports that some users have avoided CHS by switching to home-grown organic weed — which they can be certain is free of pesticides — can also be interpreted this way, Lee argues.

“There’s a huge confounding variable in saying, ‘I’ve started growing my own and the problems have gone away,’ which is that the stuff they were buying was twice as potent as what they’re growing.

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“Home growers typically don’t analyze their plants chemically: they just grow it and smoke it. Especially if it’s their first time growing their own, they’re probably not doing a very good job.”

Head says she tried switching to legal cannabis, and ended up just as sick as before.

“I stopped smoking it. I was clean for almost six months, no symptoms, no stomach issues, nothing like that. So of course I got a little cocky and thought, ‘Maybe I can have a little puff now and again. It’s not going to be an issue.'”

“It didn’t help at all. I was smoking the legalized stuff for about a month or so, and I got just as sick as when I was smoking street weed, not even knowing what’s in it.” Tweet This

As for why it afflicts some heavy users but not others, Verbora thinks it may come down to individual genetic differences in response to cannabis — much as the same joint can make one person excitable and another sedated.

“Cannabis works on the endocannabinoid system, and this system is very different in each of us. The number of receptors we all have is different. How well the cannabinoid system is functioning in all of us is different.

“We know a little bit, and there’s more that we don’t understand than we know. There are a lot of areas of research that we need to really do with this condition.”

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One puzzle is that CHS doesn’t seem to exist in some parts of the world, like Jamaica, that have a long tradition of cannabis consumption.

“It does kind of beg the question: if this happens to people who use cannabis all the time, why isn’t that happening in those areas?,” Mitchell says. “Why didn’t we hear about this so much from Amsterdam?”

In the meantime, Mitchell finds that patients sometimes get relief by rubbing hot pepper sauce on their abdomens.

“Capsaicin sauce helps with the pain,” he says. “You rub hot pepper sauce on your belly and that can help treat the pain for this kind of thing.” Tweet This

It seems to help in much the same way hot baths do.

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While doctors say they would like to know more, it seems that capsaicin (derived from hot peppers) and hot water both activate part of the nervous system called the TRPV1 receptor, which may be damaged by very heavy cannabis use.

CHS may simply work differently in different people, Verbora says. Some people are able to start using cannabis again after recovering, and others find they can’t, and have to strictly abstain.

There isn’t an overall national number of patients, but Mitchell says his hospital sees about a dozen cases a month, mostly repeats. There is about one new case a month.

“Some predicted an increase with legalization, but CHS patients usually smoke grams per day and can’t afford the legal market,” he wrote in an exchange of texts. Tweet This

“In the past, patients wouldn’t believe me because everyone knows cannabis is good for nausea. Now that there are popular articles about it added to physician awareness, it can be dealt with sooner, with fewer Emerg visits.”

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Both Zhuang and Head say they experienced cannabis as addictive, something it has a reputation as not being. (Health Canada says cannabis addiction is possible.)

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“Most people say weed isn’t addictive,” Head says.

“For most people it’s not — not everybody has these issues. But for me, and a lot of other people going through this, one turns into two, and whatever amount of weed you’re smoking turns to more, and it gets worse and worse and then you’re back to square one, where you’re sick again.”

In her case, she says addiction led to heavy consumption, up to 10 or 15 joints a day on days off, which in turn triggered the CHS.

However, both are in favour of legalization.

“We should never have made it into an illegal thing anyway,” Zhuang says. “There are so many benefits to it. There are people who genuinely need it. I think it should have been done sooner.”

Head agrees.

“I’m totally for the whole legalization thing. It’s my issue, right? I have to stay away from it. It doesn’t mean others have to.”