<p>This has been studied.</p>
<p>Via <a href="https://www.sciencedirect.com/science/article/pii/S0379073820304217" rel="nofollow noreferrer">https://www.sciencedirect.com/science/article/pii/S0379073820304217</a> :</p>
<p>Cannabis users show consistently weakened responses in pupillary light reflex tests.</p>
<p>The method is suitable for on-site detection:</p>
<blockquote>
<p>The measurements were taken using a developed version of the previous described puillograph, the F2D2 (AMTech/Dossenheim, Germany) - a portable device, which is more suitable to be used during routine police check-points.</p>
</blockquote>
<p>The method is fairly reliable (cohort size of 41, demographic factors controlled for, efficacy confirmed with blood tests).</p>
<blockquote>
<p>Abstract</p>
</blockquote>
<blockquote>
<p>Driving under the influence of alcohol (DUIA) and drugs (DUID) is considered an elevated risk for traffic safety. When assessing a driver's fitness to drive, standardized and objective measurement methods are still required, in order to clarify the question whether an individual is under the influence of substances acting on the central nervous system (CNS). We exposed healthy test subjects (n = 41) as well as persons who were under the influence of cannabis after repeated inhalation to multiple light stimuli using infrared technology and measured the pupillary light reflex (PLR).</p>
</blockquote>
<blockquote>
<p>Toxicological tests of blood samples taken from every subject followed. The aims of this study were to assess the differences in pupillography response between cannabis consumers after a washout period and no cannabis consumers as well as the dose related effects on pupillography parameters of cannabis in cannabis consumers. All four pupillary parameters changed according to a weakened pupil function after acute administration of cannabis in all test subjects. Furthermore, it could be observed that habitual cannabis consumers showed an altered pupillary function just before the first dose was taken, suggesting that the long-term effects and addiction also have to be taken into account, when effects of the CNS are discussed. The results of the present study show that almost all pupil parameters could be reliable indicators for the detection of subjects under the acute effect of cannabis.</p>
</blockquote>

CC BY-SA 4.0
2022-12-05T19:47:24.223Z
2022-12-05T19:47:24.223Z
belkarx
<p>Recently many states have legalized cannabis.  While alcohol intoxication is easy to measure, intoxication by cannabis is not.  Cannabis can stay in the blood for several months, whereas the underlying individual is most likely no longer intoxicated after several hours (see <a href="https://americanaddictioncenters.org/marijuana-rehab/how-long-system-body" rel="nofollow noreferrer">https://americanaddictioncenters.org/marijuana-rehab/how-long-system-body</a> for information as to how long cannabis can be detected in the bloodstream).</p>
<p>In <strong>Thinking Fast and Slow</strong> Daniel Kahneman describes how one can measure cognitive load while doing arithmetic problems via pupil dilation.  I am a mathematician by training and not a neuroscientist.  However, I would like to conjecture that if one could measure pupil dilation effectively enough then the rate at which one's pupils would dilate while doing an such arithmetic tasks might differ sufficiently during cannabis intoxication that one could effectively measure whether a driver was intoxicated by a &quot;roadside arithmetic test&quot; in which one would wear a special pair of glasses and perform such arithmetic tasks.  There would be potential obstacles depending on the numeracy of various people, however if it would work such a test would be far fairer to drivers than conventional methods.  Has an effort been put into creating such a test?  Would such effort be worthwhile and if so, would anyone on this forum know someone who would be interested in approaching this problem?</p>

CC BY-SA 4.0
2022-11-25T08:22:00.267Z
In his book, Daniel Khaneman seems to be referring to https://doi.org/10.1126/science.143.3611.1190 with regard to pupil dilation and cognitive load. However, there are other claims in your question which have no prior research information to back them up.
Chris Rogers
CC BY-SA 4.0
2022-11-25T18:39:23.390Z
Hi, I added a source for how long cannabis can be detected in the bloodstream.  When it comes to the claim that one is intoxicated for at most several hours I must admit that this comes from observing individuals using the substance.  If you have any evidence whatsoever that an individual is actually intoxicated for longer than 5 hours after using cannabis, I would like to see that.  The main point of this claim is that an individual may be liable under the law long after they are impaired.
Schemer1
CC BY-SA 4.0
2022-11-25T18:39:40.740Z
What other claims do not have sufficient backing?
Schemer1
<motor><behavioural-neuroscience>
Would it be worthwhile/has anyone tried to produce a machine that measured intoxication by pupil dilation while doing arithmetic?
Schemer1
# Would it be worthwhile/has anyone tried to produce a machine that measured intoxication by pupil dilation while doing arithmetic?

(Asked by: username_0 on 2022-11-23)

Recently many states have legalized cannabis. While alcohol intoxication is easy to measure, intoxication by cannabis is not. Cannabis can stay in the blood for several months, whereas the underlying individual is most likely no longer intoxicated after several hours (see <https://americanaddictioncenters.org/marijuana-rehab/how-long-system-body> for information as to how long cannabis can be detected in the bloodstream).

In **Thinking Fast and Slow** Daniel Kahneman describes how one can measure cognitive load while doing arithmetic problems via pupil dilation. I am a mathematician by training and not a neuroscientist. However, I would like to conjecture that if one could measure pupil dilation effectively enough then the rate at which one's pupils would dilate while doing an such arithmetic tasks might differ sufficiently during cannabis intoxication that one could effectively measure whether a driver was intoxicated by a "roadside arithmetic test" in which one would wear a special pair of glasses and perform such arithmetic tasks. There would be potential obstacles depending on the numeracy of various people, however if it would work such a test would be far fairer to drivers than conventional methods. Has an effort been put into creating such a test? Would such effort be worthwhile and if so, would anyone on this forum know someone who would be interested in approaching this problem?

**Tags:** motor, behavioural-neuroscience

> **Comments:**
> **username_1**: In his book, Daniel Khaneman seems to be referring to https://doi.org/10.1126/science.143.3611.1190 with regard to pupil dilation and cognitive load. However, there are other claims in your question which have no prior research information to back them up.  
> **username_0**: Hi, I added a source for how long cannabis can be detected in the bloodstream.  When it comes to the claim that one is intoxicated for at most several hours I must admit that this comes from observing individuals using the substance.  If you have any evidence whatsoever that an individual is actually intoxicated for longer than 5 hours after using cannabis, I would like to see that.  The main point of this claim is that an individual may be liable under the law long after they are impaired.  
> **username_0**: What other claims do not have sufficient backing?  

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## 1 answers

### Answer by username_2 on 2022-12-05. Score: 3 | Accepted answer

This has been studied.

Via <https://www.sciencedirect.com/science/article/pii/S0379073820304217> :

Cannabis users show consistently weakened responses in pupillary light reflex tests.

The method is suitable for on-site detection:

> The measurements were taken using a developed version of the previous described puillograph, the F2D2 (AMTech/Dossenheim, Germany) - a portable device, which is more suitable to be used during routine police check-points.

The method is fairly reliable (cohort size of 41, demographic factors controlled for, efficacy confirmed with blood tests).

> Abstract

> Driving under the influence of alcohol (DUIA) and drugs (DUID) is considered an elevated risk for traffic safety. When assessing a driver's fitness to drive, standardized and objective measurement methods are still required, in order to clarify the question whether an individual is under the influence of substances acting on the central nervous system (CNS). We exposed healthy test subjects (n = 41) as well as persons who were under the influence of cannabis after repeated inhalation to multiple light stimuli using infrared technology and measured the pupillary light reflex (PLR).

> Toxicological tests of blood samples taken from every subject followed. The aims of this study were to assess the differences in pupillography response between cannabis consumers after a washout period and no cannabis consumers as well as the dose related effects on pupillography parameters of cannabis in cannabis consumers. All four pupillary parameters changed according to a weakened pupil function after acute administration of cannabis in all test subjects. Furthermore, it could be observed that habitual cannabis consumers showed an altered pupillary function just before the first dose was taken, suggesting that the long-term effects and addiction also have to be taken into account, when effects of the CNS are discussed. The results of the present study show that almost all pupil parameters could be reliable indicators for the detection of subjects under the acute effect of cannabis.


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