Cycling, cannabis and complications of research
There have apparently been few studies on the effects of cannabis on cycling ability. Many cannabis users, recognizing that they are impaired, may choose a bicycle as a means of transportation, rather than driving. How safe is this choice?
I am unable to find any papers written about cycling and cannabis during the 20th century. There have been two papers written on the subject in the last two years.
The subject of driving and alcohol use has been much better studied, with impairment beginning at 0.02 mg/dL, less than half of the typical legal limit for driving motor vehicles.
The first article is: Cycling-related crash risk and the role of cannabis and alcohol:a case-crossover study, from Preventive Medicine, 2014.
Conclusion. Cannabis and alcohol use each appear to increase the risk of a non-fatal injury-related crash among bicyclists, and point to the need for improved efforts to deter substance use prior to cycling, with the help of regulation, increased education, and greater public awareness. However, cannabis results should be interpreted with caution, as the observed association with crash risk was contingent on how consumption was measured.
The establishment of impairment from alcohol is fairly straightforward and coorelates well with blood alcohol levels. Determining impairment from cannabis can be more difficult as impairment does not coorelate well with blood levels; THC can also persist in the blood long after impairment has disappeared.
Impairment by cannabis in this study was determined in two separate ways, by self-report and by blood test (only 39% of patients). The defining level for acute cannabis use was set in this study at 0.2 ng/L. This is a very low level (the second study notes that no impairment was found below 5 ng/mL) and most per se laws in the US are set between 1–5 ng/L. Setting the impairment standard at 0.2 ng/L risks misdefining many users as impaired when that level could have arisen from use several days previously. A much higher percentage of subjects were found to be positive by blood test than by self report. This could represent decreased disclosure on self report due to legal concerns, but could equally be due the low impairment blood standard
The results of this study were that the consumption of alcohol was associated with a fourfold increase in the risk of accident. The authors also reported that cannabis use was associated with a doubling of crash risk, although this was only when including all of the cyclists who were positive (at low levels) on their blood tests. When cannabis use was coorelated with self report, there was no increased risk of accidents. The authors conclude that while alcohol has consistently been shown to cause impairment in cyclists,
The case for cannabis is less clear. While this is the first study to examine whether acute cannabis consumption increases the likelihood that a cyclist will be involved in a crash involving injury, findings were inconsistent across models and should be interpreted with caution.
The second article is: The effect of cannabis on regular cannabis consumers’ ability to ride a bicycle from Int J Legal Med, 2016. In this study, 14 regular cannabis consumers were given up to 3 joints to smoke before undergoing medical examination and practical cycling tests.
Their abstract summary explains that:
A defined THC concentration that leads to an inability to ride a bicycle cannot be presented. The test subjects showed only slight distinctive features that can be documented using a medical test routinely run for persons under suspicion of driving under the influence of alcohol or drugs
The authors were aiming for a very high level of blood THC. They indicate that a THC level of 7–10 ng/L would not be expected to cause any impairment as this is roughly equivalent to the effects of a BAC of 0.05 mg/dL, although impairment from alcohol can definitely be seen at this level. Half of the patients in this study arrived with a THC level >2 ng/L, which would have rendered them already impaired by the definition of the first study.
An interesting wrinkle in the study was that patients were supposed to be excluded if they tested positive for other drugs, secondary testing showed that 4 out of the 14 subjects tested positive for amphetamines/MDMA. This obviously complicates the testing and it was found that those patients who tested positive for amphetamines/MDMA were less impaired that other cannabis users on ophthalmologic testing.
The authors found that the medical examination was inconsistent in revealing distinctive features of cannabis use. As far as the practical cycling tests:
Hardly any coordinative disturbances could be detected under the influence of high or very high THC concentrations…These results are in accordance with the conclusion of Robbe that a causal relationship between cannabis smoking and impaired driving or the risk of accident involvement has not been convincingly demonstrated yet.
As with driving a car, riding a bicycle when impaired by alcohol seems to produce definable impairment that can be linked to blood alcohol levels. Alcohol was has been linked to 28% of cycling fatalities. The studies above demonstrate that the same cannot be said for cannabis. Per se laws (based only on the presence of cannabis) will inevitably criminalize those who are not impaired. Better neuropsychological tests are needed to examine impairment rather than just relying on blood levels. These two studies also add further evidence to the concept that cannabis tends to produce much less impairment than alcohol. Further research into the varying effects of different substances (including common medications such as diphenhydramine) is needed to help clarify how to best deal with impairment on the roads, from cars or bicycles.