People who use cannabis on a regular basis could require up to two times the usual level of sedation when undergoing medical procedures, a small-scale study suggests.

Researchers in Colorado compared medical records from 250 patients who received general anesthesia during endoscopic procedures. Of those patients, 225 said they did not use cannabis; only 25 of the study’s cohort claimed to smoke or ingest cannabis on a daily or weekly basis.

The study found that patients who were regular pot users required 14 per cent more fentanyl, 20 per cent more midazolam, and 220 per cent more propofol to achieve the correct level of sedation for a routine procedure, such as a colonoscopy.Fentanyl, midazolam and propofol are all drugs commonly used in medical sedation.

"Cannabis has some metabolic effects we don't understand and patients need to know that their cannabis use might make other medications less effective,” said lead researcher Dr. Mark Twardowski in a statement.

“We're seeing some problematic trends anecdotally, and there is virtually no formal data to provide a sense of scale or suggest any evidence-based protocols.”

But experts note that the study is extremely preliminary and would require a much larger, more controlled study environment in order to provide firm evidence of how cannabis use may interact with medical procedures.

“I would call it hypothesis generating,” Jason Busse, associate director at Michael G. DeGroote Centre for Medicinal Cannabis Researchat McMaster University, told “This is an extremely preliminary piece of work, but it certainly suggests that this is something we should take a look at.”

Busse noted that although the study had several limitations, he agreed with the author’s point that recreational cannabis use could become more common with legalization. Tracking that data and researching the potential implications will be important for both medical protocols and patient care, he said.

Dr. Roderic Eckenhoff, a professor of anesthesia at the University of Pennsylvania who agreed that a much more robust study would be needed to draw concrete conclusions, noted that self-reporting of recreational drug use also makes studies like these difficult.

“Self-reporting especially with recreational drugs is always suspect,” Eckenhoff told, noting that even in places where pot is legal, patients may still feel stigmatized about their use.

However, the anesthesiologist noted that it is very important that patients disclose any type of recreational or prescription drug use to their physician and anesthesiologist before undergoing any medical procedure to avoid any potential complications.