By Roger Chriss, PNN Columnist

The U.S. House of Representatives voted last week for the first time to legalize marijuana at the federal level. While passage by the Senate appears unlikely, the historic House vote on the MORE Act shows how much public attitudes about marijuana have changed.

A recent Gallup poll found that 68 percent of the country now favors having legal access to marijuana. Last month voters in four states approved recreational cannabis measures, raising to 15 the number of states where cannabis is completely legal. Thirty-six states have approved it for medical use.

As cannabis use becomes more accepted and widespread, healthcare providers need to take cannabis into consideration when treating patients, especially those undergoing surgery.

The Perioperative Pain and Addiction Interdisciplinary Network (PAIN) recently convened a panel of 17 experts to develop new guidelines on the care of cannabis-consuming surgery patients. The result is a set of recommendations that include cannabis weaning before surgery and close monitoring during surgery, particularly for heavy cannabis users.

Because of the potential for cannabis to interfere with anesthesia, the guidelines recommend that patients who use a cannabis product more than 2 or 3 times per day should be considered for tapering or cessation several days before surgery. That includes patients who use more than 1.5 grams per day of smoked cannabis, more than 300 mg per day of CBD oil, or more than 20 mg per day of THC oil. Cannabis users may also need additional medication for postoperative nausea and vomiting.

There is only limited research on how cannabis interacts with analgesics and other medications. But the few studies that have been done suggest caution is warranted.

A 2006 study done in Germany looked at patients after surgery. None of the patients was able to achieve sufficient pain relief at any dose of Cannador, a cannabis plant extract. Several experienced significant side effects, including sedation and nausea. And the study had to be halted because of a severe adverse event in one patient.

A recent study at the University of Michigan looked at cannabis use and surgical outcomes in 1,335 adults undergoing elective surgery. About half reported using cannabis medically, recreationally or both. The results are concerning.

"On the day of surgery, cannabis users reported worse pain, more centralized pain symptoms, greater functional impairment, higher fatigue, greater sleep disturbances and more symptoms of anxiety and depression versus non-cannabis users,” the researchers said.

Medication use, including opioids and benzodiazepines, was also higher in the cannabis group. The study authors concluded that "cannabis users have higher clinical pain, poorer scores on quality of life indicators, and higher opioid use before and after surgery."

Another recent study at the University of Colorado Hospital was smaller and more specific, looking at 118 patients who had surgery for a broken leg. About one-fourth of the patients reported prior cannabis use. Although cannabis use was not associated with a higher dose of the anesthetic propofol during surgery, it was associated with more post-operative pain. Cannabis users also required significantly more pain medication than the control group.

Lead study author Ian Holmen, MD, told Practical Pain Management that it was important for clinicians to ask patients about their cannabis use before any surgical procedures.

“A provider just needs to know if the patient uses cannabis or not. It doesn’t matter if it’s a daily situation, just so [providers] are aware that the post-operative and possibly interoperative period are going to appear different in a patient who’s using cannabis than one who is not,” Holmen said.

Further study is needed to better understand how cannabis use affects surgical outcomes and how the effects may change at various doses of cannabis products. But the concerns of the Perioperative Pain and Addiction Interdisciplinary Network appear well-founded. Guidelines for the perioperative management of cannabis use are a necessary and useful step forward as cannabis use becomes more common.

Roger Chriss lives with Ehlers Danlos syndrome and is a proud member of the Ehlers-Danlos Society. Roger is a technical consultant in Washington state, where he specializes in mathematics and research.