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Like with all drugs we take, there are good and bad effects that come with cannabis. But a new study out Monday suggests that one of these bad side effects could be a strange tolerance to anesthesia. It found that Colorado residents who regularly use cannabis needed up to twice as many powerful sedatives before a procedure.


The Colorado-based researchers looked at the medical records of 250 patients in the state who underwent endoscopies, procedures that involve sending a camera down your throat (or other sensitive orifices) to get a closer look inside the body. They specifically searched for patients after 2012, since that’s when recreational cannabis was legalized in the state. Though it wouldn’t be officially sold in stores until 2014, patients would still presumably be more comfortable telling their doctors about their cannabis use from 2012 onward.

Those who said they took cannabis daily or weekly, the researchers found, were significantly less sensitive to several drugs across different classes used to sedate people, when compared to people who said they never used it. On average, it took 14 percent more fentanyl (an opioid), 20 percent more midazolam (a benzodiazepine), and 220 percent more propofol (a general anesthetic that can also be used for mild sedation ) to reach the right level of sedation needed for their procedures (endoscopies are typically done with mild seda tion , though some people do need or opt for deep sedation).


The findings were published in The Journal of the American Osteopathic Association.

According to lead author Mark Twardowski, an osteopathic internal medicine physician, there’s anecdotal evidence of patients who use cannabis needing more sedation to go under. But this admittedly small study (only 25 cannabis users were looked at in total) is seemingly the first to try quantifying how big of a problem it might be. And needing higher doses can certainly be more dangerous for patients, since, depending on the drug, it can increase the chances of side effects.

“Some of the sedative medications have dose-dependent side effects, meaning the higher the dose, the greater likelihood for problems,” said Twardowski in a statement. “That becomes particularly dangerous when suppressed respiratory function is a known side effect.”

Less certain is exactly how cannabis could be causing this increase in sedative tolerance. Cannabis and drugs based on it primarily interact with a unique network of receptors in the nervous system called the endocannabinoid system. This system plays a role in all sorts of bodily functions, from our sense of hunger to pain perception. But other drugs, including opioids and benzodiazepine, also interact with these receptors. And there might be other ways that weed could be causing these side-effects.


“This study really marks a small first step,” said Twardowski. “We still don’t understand the mechanism behind the need for higher dosages, which is important to finding better care management solutions.”

What the study does clearly suggest, as others have, is that there’s still a lot we don’t know about cannabis’ effects on the body. That’s largely the fault of federal law that continues to classify cannabis as a drug with no medical applications, preventing and slowing down research. But all for the good that cannabis and cannabis-based products can do, that lack of knowledge also stops us from spotting the less rosy consequences of cannabis use.


Twardowski and his team hope to continue studying the link between cannabis and sedative tolerance (including its effect on deep sedation) , as well as whether cannabis can also affect how pain is managed following medical procedures.