Drug Driving

A new law has come into effect that means police officers can now test for, and prosecute, drug diving offences.  ACPO have welcomed the developments  as all of us should really.

The sky news report inevitably raises the idea of zero tolerance, of which I have spoken before.  This got me thinking about one particular drug, cannabis.  If this policy is to be truly a zero tolerance policy, which I seriously doubt for most police force areas, then I have been thinking about the dangers of passive smoking.

Now many will already be thinking  'this doesn't apply to me' I'm a respectable person who doesn't know anyone who smokes cannabis, and perhaps for some this is true.  However, many of us though have been walking down the street and all of a sudden an 'interesting smell' (makes me think of very sweet garlic combined with basil, how middle class!) assaults our nostrils.  Perhaps it's a reflection of where I live, but it is not infrequent round my way.  (Indeed a small cannabis factory was closed by police just a few weeks back round the corner from me).

So I do wonder what effect walking past someone who is actively smoking a spliff (or whatever they are called nowadays) would have on my driving ability.  Would it put me over the drug driving limit? how long should I leave it before getting in my car?  (These are all equally valid questions for the drink driving issue when a zero limit is proposed, although obviously one can't passively ingest alcohol!). I have asked a couple of police twitter accounts and the DFT twitter account this morning but haven't received an answer (hardly surprising they probably get such requests daily) so I thought I would do a bit of looking.

There is evidence to suggest that zero tolerance should be adopted when considering the effect even small levels of cannabis can have on driving performance, although the new laws have not adopted this approach.

The regulations prohibit driving with a limit of 2 microgrammes per litre of blood for THC (Active ingredient in cannabis).  According to a study in the Journal of Analytical Toxicology in 1987 high cannabis use in enclosed environments can lead to high THC levels in urine of passive smokers, although as the authors point out it would be quite uncomfortable in such an environment given the level of pot that was likely to be swirling round the room.  With lower exposure (4 passive cigarettes) there was  infrequent positive testing and generally tests were neutral, make of that what one will (inconclusive I would say and unlucky for some in the current context).  Although it is worth pointing out that the subjects in the experiment were still in an un-ventilated room with the smoker

A study in 2011 examining the inhalation of passive cannabis smoke in dutch coffee shops showed that THC was present in saliva above the legal limit (proposed in the current law) in most participants at 40 minutes exposure.  It is worth pointing out in this study that two locations were used, a larger cafe with more smokers, and a smaller one with less smokers, both produced positive results, although it seems that the smaller the environment the higher the THC levels (with lesser active smokers).

A similar study in 2010  also found levels of THC about 2ng/ml (the drug driving legal limit) from passive cannabis inhalation in a dutch coffee shop at 3 hour exposure, although the authors accepted that the study did not note (unlike the 2011 one) how much cannabis was smoked by other users of the coffee shop.

So it would appear that it is possible to be above the legal limit from passive smoking of cannabis, however unless you are friends with some pretty heavy users it is unlikely you will fall foul of the legislation.  I for one am not too worried now about the funny smells in my neighbourhood giving a false positive.

So what have we learned from this?  Firstly the law is not, despite what policy makers may claim or newspapers report, zero tolerance, there is a tolerance of up-to 2 microgrammes per litre of blood.  You are unlikely to be over this level unless you have spent a bit of time in a Dutch coffee shop, caught an immediate flight home and then decided to drive from the airport (perhaps a taxi might be in order).  Alternatively if you know people who are heavy users then please for everyone's sake do not drive and do not let your friends drive.

Secondly I have also learnt that if you want the thrill of cannabis use without actually buying it yourself Dutch coffee shops seem a good place to visit!