Cannabis and cigarettes may not impact overall recovery periods for patients affected by concussions, but they could impact symptom burdens, according to a recent U of T-affiliated study.

Dr. David Lawrence, a staff physician at the MacIntosh Sport Medicine Clinic and the lead primary care physician for the Toronto Blue Jays, spoke with The Varsity about the impact of the recent study he co-authored.

Cannabis, cigarettes may still impact symptom burden of concussions

The main conclusion of the early study was that cannabis, alcohol, and cigarette use did not impact the recovery period of patients who suffer from concussions. This was found using surveys taken four weeks after sustaining an injury.

However, the co-authors found that cigarettes caused a heavier symptom burden of concussions, defined as the subjective prevalence, frequency, and severity of symptoms, among the study’s participants within the first week after sustaining injury. They also uncovered an association between cannabis use and a lighter symptom burden of concussions, according to the assessments taken at the end of the third and fourth week.

Symptom burden is just one aspect of physician-determined recovery, which the co-authors used to measure the recovery period.

“Other factors that go into physician determination of recovery include their functional status, their [pre-existing injuries] and also any other complaints that they might have at the time,” remarked Lawrence.

Another important finding, noted Lawrence, was that the patients had a high prevalence of using cannabis, alcohol, and cigarettes. Around one in four participants reported regular cannabis use, one in two reported regular alcohol use, and one in five reported regular cigarette use in the month preceding their injury.

Lawrence noted that it could be useful for physicians to ask their patients about their substance use, which could be useful in making medical assessments.

The limitations of the study

Lawrence remarked that the study has a number of limitations, as it is one of the earliest studies on the impact of cannabis on concussion recovery.

The co-authors recruited 307 patients who reported acute concussions at the clinic to the study. “We followed them for a minimum of four weeks, or until they were cleared,” noted Lawrence.

During the study’s duration, the co-authors gathered data from the participants through self-reports to determine substance use. However, self-reports are impacted by social desirability, whereby participants may be dishonest in their survey responses, or they might give incorrect information due to misremembering.

Lawrence noted that another limitation stemmed from the low cut-off  for alcohol use, which was defined as  the regular consumption of two or more standard alcoholic drinks for at least two days per week.

This definition enabled the researchers to capture a wide range of alcohol users, but Lawrence noted that it also categorized data from moderate drinkers with heavier drinkers in the same group.

Finally, a third limitation stemmed from a lack of data that could identify why cannabis and cigarettes impacted symptom burden without influencing overall recovery. Future studies could uncover the reason behind these results.

The potential impact on clinical practice

Lawrence noted that the study should not change clinical “recommendations with respect to use of these substances at this time.” He recommends patients to continue avoiding these substances while recovering from concussions, following standard guidelines on recovery.

“What this study does do is… [allow physicians] to potentially reassure [patients] to say, ‘look, if you’ve used the substance, you probably haven’t delayed your recovery,’” said Lawrence.

“But we would still recommend to [stop] use until further research supports or negates their use.”