Marijuana use before surgery can worsen pain during recovery, study finds

  • US researchers recently studied the difference in pain levels between marijuana users and non-users before and after surgery
  • Patients who used marijuana before surgery required higher levels of anaesthesia
  • The lead researcher stressed the importance of patient honesty when undergoing surgery

Marijuana, also referred to as cannabis, pot, weed or dagga, has become popular across the world for its pain-relieving properties. But, according to a recent study, smoking or ingesting it in the hope of managing your pain after surgery might end up doing quite the opposite.

"There is some evidence that cannabis may be beneficial for chronic and nerve pain. However, early research suggests that this is not the case for acute pain such as for surgery of a broken leg," said lead author Dr Ian Holmen, an anesthesiology resident at the University of Colorado Hospital in Aurora, in a statement published by the American Society of Anesthesiologists (ASA).

The research was presented at the ASA’s annual meeting this month.

An additional surprising finding was that, apart from an increase in acute pain, people who used marijuana before surgery also ended up requiring more anaesthesia during surgery, and used more painkillers during recovery.

Researchers said that this was especially concerning, as undergoing anaesthesia is risky for certain patients, such as the elderly and those with chronic illnesses like diabetes.

The study

For their study, the research team studied the charts of 118 patients who had undergone surgery at the University of Colorado Hospital to repair a fractured tibia. They found that 30 (25.4%) patients had reported using cannabis prior to surgery.

The type and method of cannabis use, as well as how frequently it was used, were not known.

After comparing the two groups (users versus non-users) by assessing the amount of anaesthesia provided during surgery, patient-reported pain scores, and dosage of painkillers consumed in the hospital after surgery, they found the following in patients who had used cannabis before surgery:

  • They used 58% more painkillers per day while in the hospital
  • They reported higher levels of pain (on a scale of 1 to 10)
  • They required an additional 12.4 millilitres of anaesthesia during surgery than those who did not use marijuana

Holmen commented that cases like these emphasise the importance of patients answering pre-op questions honestly, as this information can inform doctors on their patients’ drug use and influence the amount of anaesthesia required during surgery, as well as their recovery plan.

Encouraging further research

Researchers looking into patients who chronically use opioids (painkillers) before surgery already know that these patients have exaggerated pain responses post-surgery, due to an increased tolerance, and therefore need increased pain medication.

"We speculate that cannabis use may cause a similar effect, but we need more research to determine if this is the case," Holmen said.

READ | Cannabis may not be great for your heart

READ | Medical pot may help many battle insomnia, pain and stress

READ | Marijuana withdrawal is real, study shows

Image: M. Maggs/Pixabay 

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