The major findings of the present study were the cannabis-related impairments with some deficits up to 12 hours after consuming one marijuana cigarette. Blood THC levels were significantly higher at 1-hour post-consumption compared to baseline but there were no significant differences between baseline measures versus 6- and 12-hours. Blood Carboxy-THC Levels followed a similar trend but did not achieve statistical significance. The hypothesis was partially confirmed as smoking cannabis increased systolic blood pressure (1-hour), heart rate (1- and 6-hours), force variability when attempting to maintain 40% MVIC (1- and 6-hours) as well as decreases in RFD (50-, 100-, 150- and 200-ms) at all force-time periods (6- and 12-hours), 40% MVIC endurance time (12-hours) and associated endurance task EMG (12-hours) and eyes open non-dominant leg balance (1-, 6- and 12-hours). Although the participants expressed minimal to no perception of intoxication at 12 hours post-consumption, there were still negative physical performance manifestations.
The increase in heart rate (tachycardia) and blood pressure (hypertension) are in accord with prior studies. Hindocha et al.’s (Hindocha et al. 2017) participants, who smoked a mixture of 66.67 mg cannabis and 311 mg tobacco were tested within an hour experiencing increases in heart rate and diastolic blood pressure, but no significant change in systolic blood pressure. In another study, three experienced marijuana smokers (averaged 4.7 marijuana cigarettes per month) smoked 4 marijuana cigarettes (2 each at 9:00 and 13:00) with concentrations of 2.57% THC and were tested over 6 hours on day one as well as the following day. Similar to the present study, heart rate was elevated immediately after smoking and returned to baseline after 6 hours (Heishman et al. 1990). After vaporizing and smoking cannabis containing THC doses of 0, 10, and 25mg, heart rate peaked within 30-minutes and returned to baseline within 3- to 4-hours (Spindle et al. 2018). A review by Franz and Frishman (Franz and Frishman 2016), reported that marijuana cigarettes increase heart rate, supine systolic and diastolic blood pressures, and forearm blood flow due to increased sympathetic nervous system activity. Complications include a decreased time to exercise-induced angina with stable angina patients and an association with triggering myocardial infarctions in young male patients (4.8-fold greater incidence for 1-hour after marijuana consumption) due to coronary arterial vasospasm. Hence, individuals who experience chronic tachycardia and hypertension should carefully consider the effects of cannabis and perhaps refrain from cannabis use.
While cannabis use is more prevalent in some high-risk sport athletes there is no direct evidence of athletic performance-enhancing effects (Ware et al. 2018). To the contrary, there seems to be overwhelming evidence for performance impairments, with the present study highlighting difficulties with matching and maintaining a 40% MVIC force. Chung et al. (Chung et al. 2020) demonstrated that young adults’ acute subjective marijuana “high” (intoxication) impaired performance with visuospatial working memory, information processing and psychomotor speed (digit symbol substitution task), which were related to slight decreases in cognitive functioning. Marijuana decreased the accurate detection of circular lights on the first day of testing but not the second day (Heishman et al. 1990). Cognitive and psychomotor deficits peaked at 30-60-minutes post-cannabis administration, not returning to baseline for 6 to 8 hours in some cases (Spindle et al. 2018). Very high dosages can cause persistent, negative effects on verbal and visual memory, executive functioning, visuoperception, psychomotor speed, and manual dexterity (Bolla et al. 2002).
In terms of motor control, driving performance (as example of a complex motor task involving integration of both sensory and motor control) under the influence of cannabis has been comprehensively investigated. A narrative review by Bondallaz et al. (Bondallaz et al. 2016) reported dose-dependent impairments in road tracking due to increased lane position variability and deficits in the ability to maintain a constant velocity suggesting alterations in the activation of specific brain areas and networks that are adversely affected by cannabis smoking. They reported that days after discontinuing cannabis consumption, driving skills were still negatively affected, proposing that more complex tasks may be affected for longer durations (Bondallaz et al. 2016). Another narrative review by Chow et al. (Chow et al. 2019) indicated that whereas acute and infrequent cannabis use can induce cognitive and psychomotor impairment when driving, this is not consistently the case for chronic heavy use. McCartney et al.’s (McCartney et al. 2021) systematic meta-analysis found that regular cannabis users experienced fewer driving impairments than occasional cannabis users. Their systematic review suggested that individuals should wait at least 5-hrs following inhaled cannabis use before performing safety-sensitive tasks. Another review by Arkell et al. (Arkell et al. 2021) reported that THC impairs driving performance and can increase crash risks for up to 8-hours especially with occasional users. Ogourtsova et al. (Ogourtsova et al. 2018) found that with young recreational cannabis users, smoking a 100-mg dose of cannabis had no significant effect on simple driving-related tasks, but there were significant deficits with complex tasks, which persisted up to 5 hours after use. The Prashad and Filbey (Prashad and Filbey 2017) review states that cannabis use affects cortico-striatal networks that are essential for producing movement. Hence, our findings of persistent (6 hours) motor control deficits in regular cannabis users also emphasizes that tasks involving precision with submaximal intensity contractions should not be performed for at least 6-hours after smoking.
Although there was no significant effect on reaction time in the present study, RFD was adversely affected for up to 12 hours post-consumption. In contrast, Hindocha et al. (Hindocha et al. 2017) found a prolonged reaction time in a spatial working memory test after smoking 16.1% THC in regular consumers (≥once per month and ≤ 3 times a week). Reviews also report cannabis-induced reaction time impairments in Canadian (Brubacher et al. 2020) and Muslim (Nassif 2021) youth. However, Kvolseth (Kvalseth 1977) had six experienced marijuana users induce 0, 6.5, and 19.5–26.0 mg THC with no effects on simple and complex reaction time but participants did experience increased error rates for the linear and rotary movements as the dose level increased. Based on the present results, while simple reaction time was not affected with regular cannabis users, activities that involved either focus and muscle contraction with a 40% MVIC load (match a force line on a screen) or maximal RFD to produce a peak load were impaired. According to Prashad and Filbey’s (Prashad and Filbey 2017) review, whilst many reaction time studies do not report significant deficits, impairments were apparent with tasks that require focus and critical decision making.
Hence, while cannabis-induced deficits are more pronounced with more cognitively complex tasks like driving (Bolla et al. 2002; Bondallaz et al. 2016; Chung et al. 2020; Ogourtsova et al. 2018), the present results reveal that activities involving either precision (motor control) or maximal RFD with force can also be negatively impacted. Compared to low load tasks that can be accomplished with low motor unit recruitment and rate coding involving low levels of muscle activation, maximal RFD involves high motor unit recruitment especially of type II motor units firing at higher frequencies and synchronization (Behm 1995, 2004; Behm and Sale 1993).
MVIC forces and EMG activity were also not adversely affected by the cannabis, which is partially in accord with the Burr et al. (Burr et al. 2021), review that generally demonstrated either null or detrimental effects on exercise performance in strength and aerobic-type activities. As the MVIC was only a 4-second duration, impairments to focus and concentration would probably not have a substantial impact on corticospinal excitability or muscle activation.
Only one of the four balance tests, (eyes open with non-dominant leg) at 1-, 6- and 12-hours) displayed a deficit. Balance is controlled by sensory (vision, proprioception and vestibular components) and motor responses to the perceived perturbation to the equilibrium (Anderson and Behm 2005; Ferber et al. 2002; Hrysomallis 2011). When balance is perturbed, the system needs to respond quickly (reaction time) with appropriate muscle contractile force (strength) to offset the perturbation (Anderson and Behm 2005). While RFD was adversely affected, muscle strength (MVIC peak force) and reaction time were not significantly impaired by the cannabis inhalation, which generally seemed sufficient to maintain a similar duration of balance in three of the four tests.
Exercise endurance was only adversely affected at the 12-hours post-consumption period. There is scant literature on the effects of cannabis on muscular endurance. A single cannabis dose (35 mg of inhaled vaporized 18.2% THC cannabis) had no significant or meaningful effect on exercise endurance in adults with advanced chronic obstructive pulmonary disease (COPD) (Abdallah et al. 2018). We expected significant endurance impairments at 1- and perhaps 6-hours post-inhalation as the task was a continuation of the 40% MVIC force matching task, which showed significant impairments and thus would have involved focus and concentration that typically is adversely affected by cannabis (Arkell et al. 2021; Bolla et al. 2002; Chung et al. 2020; Crane et al. 2013; Hart et al. 2001). However, in addition to the need for focus and concentration to maintain the 40% MVIC force output, there would also be discomfort and pain from the prolonged exertion (86.8 ± 50.4–106.2 ± 73.9-s). The pain would arise from activation of nociceptors by the increased acidity (H + ion accumulation), contraction-induced ischemia, prolonged pressure, and other factors (Astokorki and Mauger 2017; Behennah et al. 2018; Ciubotariu et al. 2004) that could decrease corticospinal excitability to the affected muscle fibers (Del et al. 2007). The present results did show diminished EMG activity during the endurance task. As cannabis can decrease pain (Legare et al. 2022; Pantoja-Ruiz et al. 2022), it may have offset the debilitating effects of pain on corticospinal excitability (Del et al. 2007) and perception of effort (Steele 2020) for the first 6 hours of testing. At 12 hours, the pain modulation may have desisted and difficulties with focus, attention and concentration may have played a greater role.
Moreover, this study demonstrated significant temporal changes in the concentrations of THC and its metabolite Carboxy-THC following cannabis consumption, with blood THC levels peaking sharply at one-hour post-consumption indicating the peak absorption phase of the compound. There was a non-significant higher level of blood Carboxy-THC at 1-hour post-consumption. The gradual decline in mean blood THC and Carboxy-THC levels at 6 and 12 hours, suggests the progression of metabolic clearance, while high inter-individual variability underscores the complex nature of THC pharmacokinetics. The urine analysis for Carboxy-THC presented a non-significant trend over time, suggesting delayed excretion. These differences may be influenced by a range of factors, including individual metabolism rates, body composition, frequency of use, and dosage consumed. These pharmacokinetic patterns underscore the rapid absorption and metabolism of THC, followed by the more prolonged presence of its metabolite, which could have implications for detection and interpretation of cannabis use in various contexts.
It's worth noting that the saliva test kit we used to detect THC levels at multiple time intervals post-consumption failed to detect THC, leading to its classification as not useful for our purposes. This outcome contrasts with findings from three other studies, which demonstrated the utility of saliva tests in detecting THC. For instance, a study found that saliva THC levels could reflect impairment in simulated driving scenarios (Di Ciano et al 2023). Another study introduced a novel biosensor technology capable of detecting THC in saliva with high sensitivity, suitable for roadside testing (Lee et al 2016). A different study presented a rapid, non-invasive electrochemical sensing system, confirming the ability of saliva tests to identify THC levels correlating with intoxication (Churcher et al 2023). Despite the positive outcomes in these studies, our research encountered limitations with the saliva test kit used, suggesting potential variability in test sensitivity or methodology. In discussing these results, it's crucial to consider the specific conditions and technologies employed in each study, which may account for the discrepancies observed. This comparative analysis not only highlights the challenges of developing reliable saliva-based THC tests but also underscores the need for further validation and standardization in this area to ensure consistent and accurate detection across different testing platforms.
Relevance to Cannabis Consumers and Testing, Clinical and Legal Implications:
Urinalysis testing in the workplace has been adopted widely by employers in the United States to deter employee drug use and promote ‘drug-free’ workplaces. Urinalysis testing is not recommended as a diagnostic tool to identify employees who represent a job safety risk from cannabis use. Blood testing for active THC can be considered by employers who wish to identify employees whose performance may be impaired by their cannabis use (Macdonald et al 2010). Blood levels may be useful for official reporting but are not reliable for determining whether an individual is impaired. This can only be accomplished with neurocognitive testing. There can be no assurance that neurologic effects in a given consumer will not persist from the inter-shift period into the following workday (Goldsmith et al 2015). In Canada, an oral fluid drug screener is also used by law enforcement to determine driving impairment. It can detect the presence of some drugs in oral fluid, including THC (Government of Canada).
Limitations
There are some limitations to our study to acknowledge. The present study results apply to regular users as it was difficult to find individuals who were infrequent users of cannabis. From our experience in the recruitment process, individuals either used cannabis regularly or almost not at all. It would have been interesting to compare frequent and infrequent users but we were not successful in that endeavor. The 12-hour testing period was not conducive for everyone and thus although our statistical power analysis indicated sufficient numbers of participants, more participants may have provided even greater statistical power. Data was collected in a gymnasium, which is not a typical environment for a recreational cannabis smoker and thus the unfamiliar environment may have impacted the subjective feelings of intoxication. Participants smoked cannabis around other participants that they did not know and this could have affected their subjective feelings as well. It would be valuable to explore physical tests more similar to the work environment or real-life scenario such as dynamic (timed up and go) instead of static balance, an agility test instead of only reaction time, and some cognitive tasks such as the Stroop word color test or trial making test. Using these approaches, it will be possible to evaluate if the results found in this study are similar using more complex tasks. Another limitation is the smoking of only one cigarette (low dosage), which may not be similar to the typical dosage of frequent cannabis users.