Thursday, June 16, 2016

The real risks of drug driving and drunk driving

With the NSW police tripling their drug-driving tests, especially targeting cannabis, it's worth noting the actual risks involved.

In summary, cannabis increases the risk of a fatal accident: 1.8x

Opioids (which are legal): 3x

Stimulants including meth: 3.7x

Benzos (Valium etc, also legal): 4.8x

Alcohol at .02 Blood Alcohol Content (BAC) - which is legal for most drivers: 4x

Alcohol at 0.8 BAC: 13x

Alcohol at 0.16 BAC: 35x

[As an interesting aside, people with Sleep Apnea are 7-8 times more likely to crash a car than people without the condition - As reported on ABC's PM program 4/7/2016]

Full details below courtesy of Paul Dessauer:

Drug use and fatal motor vehicle crashes:
A case-control study.
Guohua Li et al
Accident Analysis and Prevention Sept 2013

<<< ABSTRACT Drugged driving is a serious safety concern, but its role in motor vehicle crashes has not been adequately studied.
Using a case-control design, the authors assessed the association between drug use and fatal crash risk. Cases (n=737) were drivers who were involved in fatal motor vehicle crashes in the continental United States during specific time periods in 2007, and controls (n=7719) were participants of the 2007 National Roadside Survey of Alcohol and Drug Use by Drivers. Overall, 31.9% of the cases and 13.7% of the controls tested positive for at least one non-alcohol drug. The estimated odds ratios of fatal crash involvement associated with specific drug categories were 1.83 [95% confidence interval (CI): 1.39, 2.39] for marijuana, 3.03 (95% CI: 2.00, 4.48) for narcotics, 3.57 (95% CI: 2.63, 4.76) for stimulants, and 4.83 (95% CI: 3.18, 7.21) for depressants. Drivers who tested positive for both alcohol and drugs were at substantially heightened risk relative to those using neither alcohol nor drugs (Odds Ratio=23.24; 95% CI: 17.79, 30.28). These results indicate that drug use is associated with a significantly increased risk of fatal crash involvement, particularly when used in combination with alcohol. >>>

Full text available;​

Drivers who tested positive for cannabis (detected either as actual THC in blood or THC-COOH metabolites in saliva) were found to have a 1.81:1 odds ratio – this equates to roughly an 81% greater chance of a fatal accident. Another way to express this is that a driver’s current cannabis intoxication increases the risk of road fatality by 1.8 times.

The study also examined prescribed pharmaceuticals and illicit drugs in the following classes;

Opioids such as morphine, oxycodone and hydrocodone were found to have an odds ratio of 3.03:1, ( or three times the risk) of fatal crash.

Stimulants such as methamphetamine, dexamphetamine, methylphenidate and phentermine have a 3.57:1 odds ratio, ( >three and a half times the risk)

Benzodiazepines such as valium or alprazolam registered a 4.83:1 risk, (nearly five times the risk).

The study compared these risk levels to alcohol, alone and in combination with other substances;

Alcohol, absent any other drug in the driver’s system, had an odds ratio of 13.64:1 (more than thirteen and a half times the risk of a sober driver).

This risk was even worse in drivers with alcohol and other drugs in their system- averaged over all it was 3.41:1.
Cannabis plus alcohol recorded the highest risk of all- this combination had an odds ratio of 23.24:1 (which is roughly equivalent to the risk associated with a driver who has not consumed cannabis or any other drugs, but who has a blood alcohol level of 0.1)

Just to put these figures into perspective, cannabis alone increased the risk of a fatal collision by 1.8 times.

Drivers with a blood alcohol content of 0.02 (BAC)  have a risk of fatal collision 4 times greater than sober drivers.
(Of course, in Australia we let people with a BAC of up to 0.05 drive on our roads every day).

A blood alcohol level of 0.08 BAC increases risk of fatality 13 times.
(In many US states this is still the legal limit).

A BAC of 0.12 increases risk by 25 times.

A BAC of 0.16 increases risk 35 times.

Alcohol intoxication is responsible for approximately ¼ of all motor vehicle fatalities.

There is an excellent discussion of cannabis, alcohol, and motor vehicle fatalities, including some of the confounders, (such as age and gender), and the uncertainties (eg serum levels of THC are a less effective measure of impairment than blood alcohol levels),  here;

Please be aware that I do not endorse driving under the influence of any psychoactive drug. Except perhaps coffee.
Please be aware that I do endorse and advocate for evidence-based policy.

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