Driving and Cannabis - Not so safe after all (queue common sense arguments)

**Toker** · 02-16-12, 01:49 PM

Originally Posted by Alundil

Heh - yet the fact remains that this was published in a Scientific magazine, and a well respected and oft cited one at that. Smacks of "don't like the content so attack the source"

?

Isn't that a non-starter in this forum?

Doesn't really make it a good article by default, because of the source.

**SmokenScion** · 02-16-12, 04:18 PM

they narrowed the feild of research from 200 something to 9 based on what evidence was provided that matched their hypothesis. Its not hard to do and Why it makes it into journal of sciences baffles me.

**Alundil** · 02-16-12, 04:53 PM

Originally Posted by Toker

Doesn't really make it a good article by default, because of the source.

That's a valid statement - though the logical extension of that would be to call into question a lot of other peer reviewed/published articles or journals simply by because of their publication in said scientific mag/journal. That's can of worms that I am certain many people all over, but especially on this forum, don't want to open.

Here's a link to the abstract and full article.
Acute cannabis consumption and motor vehicle collision risk: systematic review of observational studies and meta-analysis | BMJ

Originally Posted by SmokenScion

they narrowed the feild of research from 200 something to 9 based on what evidence was provided that matched their hypothesis. Its not hard to do and Why it makes it into journal of sciences baffles me.

You are misrepresenting that statement and taking it out of context. I don't think you read the abstract, much less beyond that line in the article itself.

Here's the abstract for you:

Objective
To determine whether the acute consumption of cannabis (cannabinoids) by drivers increases the risk of a motor vehicle collision.

Design
Systematic review of observational studies, with meta-analysis.

Data sources
We did electronic searches in 19 databases, unrestricted by year or language of publication. We also did manual searches of reference lists, conducted a search for unpublished studies, and reviewed the personal libraries of the research team.

Review methods
We included observational epidemiology studies of motor vehicle collisions with an appropriate control group, and selected studies that measured recent cannabis use in drivers by toxicological analysis of whole blood or self report. We excluded experimental or simulator studies. Two independent reviewers assessed risk of bias in each selected study, with consensus, using the Newcastle-Ottawa scale. Risk estimates were combined using random effects models.

Results
We selected nine studies in the review and meta-analysis. Driving under the influence of cannabis was associated with a significantly increased risk of motor vehicle collisions compared with unimpaired driving (odds ratio 1.92 (95% confidence interval 1.35 to 2.73); P=0.0003); we noted heterogeneity among the individual study effects (I²=81). Collision risk estimates were higher in case-control studies (2.79 (1.23 to 6.33); P=0.01) and studies of fatal collisions (2.10 (1.31 to 3.36); P=0.002) than in culpability studies (1.65 (1.11 to 2.46); P=0.07) and studies of non-fatal collisions (1.74 (0.88 to 3.46); P=0.11).

Conclusions Acute cannabis consumption is associated with an increased risk of a motor vehicle crash, especially for fatal collisions. This information could be used as the basis for campaigns against drug impaired driving, developing regional or national policies to control acute drug use while driving, and raising public awareness.

**SmokenScion** · 02-16-12, 05:03 PM

I read the full page.

Study selection

Our literature search found 2975 studies; we selected 222 for abstract review, and brought forward 23 for full text review. We identified another 16 studies from reference searching. One paper from the reference search was selected for inclusion, together with nine from the full text search (fig 1⇓).

We excluded studies after full text review that analysed the presence of inactive metabolites of tetrahydrocannabinol, or those with urine and blood test results that could not be separated. Although three of the included studies did test for the presence of cannabinoids in urine, we included data only if the presence of the active metabolite was also confirmed by a blood sample.23 39 42 After data extraction, we excluded another study because it contained duplicated data from a previous paper (fig 1).

link

What this section says is they rated the data, then through it out because it didn't match the findings of what the results are that they wanted.

**SmokenScion** · 02-16-12, 05:09 PM

http://www.bmj.com/highwire/markup/5...00&iframe=true

The Data setting for all of these Studies are inconclusive of the entire driving involvement. It is a statement of Emergency services, and the reporting system.

**SmokenScion** · 02-16-12, 05:17 PM

The Limitations Section is best.

Limitations

Legal thresholds for driver impairment due to cannabis consumption are inconsistent; the judgment of impairment varies in different regions, from observed impairment via sobriety test results only to measured tetrahydrocannabinol amounts in the blood or serum of 7-10 ng/ml.56 Furthermore, such thresholds are less meaningful in view of evidence indicating that cannabis impairment can be at its peak despite low measurements of tetrahydrocannabinol in the blood.58 Furthermore, the presence of cannabis at the time of a collision is calculated differently across studies (on the basis of serum, whole blood, or self report), and could include subjective measures of acute consumption or recent use. Several jurisdictions have attempted to legislate cannabis use by drivers by using a zero tolerance policy50 our review lends weight to their assumption that recent cannabis use increases motor vehicle collision risk. However, the studies in our review did not have enough data on tetrahydrocannabinol concentration to examine dose-response effects. Therefore, our data cannot assess legislation based on legal thresholds of cannabis impairment.

We found considerable heterogeneity across the studies in our review (I2=81%). We used a random effects model after postulating a priori that our populations would be heterogeneous, because of varying data sources and the differing methods used to measure tetrahydrocannabinol concentrations. Although we defined high quality studies as those that scored full marks on the Newcastle-Ottawa scale, many of these high and medium quality studies probably did not control for all possible confounders. Although we restricted positive cannabis results to drivers that showed the presence of tetrahydrocannabinol in the absence of other drugs or alcohol, other potentially important confounders were probably not controlled for. These hidden confounders, as well as the differing study designs used, might have affected the results of the individual studies and hence the estimates of the pooled odds ratios.

Using our inclusion criteria, we selected only studies of serious injuries and deaths resulting from motor vehicle collisions. Cannabis might also be a risk factor for minor collisions, although the association between cannabis consumption and collisions was significant for fatal motor vehicle collisions, and not significant for non-fatal crashes. Tetrahydrocannabinol concentrations might also be important, with minor collisions more likely than fatal collisions to involve drivers with lower concentrations of cannabis. Future reviews could assess minor collisions with control groups drawn from the general driving population.

source

**Bane** · 02-16-12, 05:20 PM

Oh really now.... How about this. If you take anything that can impair your perception and cognitive thinking abilities you should not be able to drive until it's out of your system. Plain and simple.

**Toker** · 02-16-12, 05:28 PM

Originally Posted by Bane

Oh really now.... How about this. If you take anything that can impair your perception and cognitive thinking abilities you should not be able to drive until it's out of your system. Plain and simple.

Driving and Cannabis - Not so safe after all (queue common sense arguments)-orly-gif

So, that would eliminate almost everyone on the road, because almost everyone is using caffeine, which enhances road rage, anti-depressants, which can slow reaction time, and a host of other legal drugs which impair mental function. One out of every four Americans take some type of drug on a daily basis...

**SmokenScion** · 02-16-12, 05:30 PM

So vote yes on MOAR public transportation.

**Alundil** · 02-16-12, 05:34 PM

Originally Posted by SmokenScion

I read the full page.

link

What this section says is they rated the data, then through it out because it didn't match the findings of what the results are that they wanted.

And I disagree with your interpretation of what the reduction in number of candidate studies means or the implications thereof. If you're attempting to study a fairly narrow subset of an already narrow subset of data, you must narrow the sources that are evaluated down as much as possible otherwise there will be a lot of unnecsessary "noise" in the data related to factors that are not relevant. You can spin that if you'd like, but the point is this: If I am going to study severe crashes and fatality crashes that involve cannabis, I cannot also include data that, on its face, obscures the very factors that I'm trying to study (those factors being alcohol and/or other illicit drugs, medical conditions unrelated to cannabis, etc). You seem to be implying that because they narrowed the amount of data/studies looked at for this paper, that their results are somehow invalid or tainted because of that. Every study does something like this when they are looking for very specific data about a small group that resides in another small group. Otherwise they are wasting their time.

Originally Posted by SmokenScion

http://www.bmj.com/highwire/markup/5...00&iframe=true

The Data setting for all of these Studies are inconclusive of the entire driving involvement. It is a statement of Emergency services, and the reporting system.

And that statement speaks, precisely, to the issues that I mentioned in terms of capturing the "real" picture of what's going on due to obvious limitations of the methods of reporting.... and the List of Limitations does as well.

Those things support the statements I made to Toker earlier.