Cannabis or Marijuana

According to Goldfrank’s Toxicological Emergencies[1] cannabis produces variable psychological effects.  The variation, which occurs both between and within users, may be a result of drug tolerance, level or phasing intoxication, physical and social settings, or user expectations of cognitive set.  The most commonly self-reported effect is relaxation. Other commonly reported effects are perceptual alterations (heightened sensory awareness, slowing of time), a feeling of well-being (including giddiness or laughter) and increased appetite.

Cannabis also has physiologic effects. These effects involve cerebral blood flow, the heart, the lungs and the eyes in the following manner:

  1. Cerebral blood flow is increased.
  2. Heart rate is increased.
  3. Blood pressure is decreased due to decrease in vascular resistance.
  4. Decreased airway resistance and an increase in airway conductance.
  5. Conjunctival injection and decreased intraocular pressure.

Cannabis and driving has been evaluated.  Neither experimental nor epidemiologic studies have provided definitive answers about what effects cannabis use has on driving ability.

The epidemiologic studies evaluating the association of cannabis use and traffic crashes provide no evidence that cannabis alone increases the risk of causing fatal crashes or serious injuries.

Of course, various eye conditions including strabismus and amblyopia severely and negatively impact upon this test.

All of these conclusions and many others can result in HGN which is indistinguishable from that caused by the consumption of alcohol.

Therefore, the appreciation of nystagmus in an individual is not a very specific test.  There are a lot of false positives when searching for alcohol intoxication with this test.  The test for nystagmus is too non-specific, producing a very high error rate when used for the purpose of determining alcohol intoxication, let alone the degree of alcohol intoxication.

      Obviously, it is impossible to develop a methodology to reliably ascertain nystagmus short of electronystagmography and even with that, it is not possible to determine the etiology without much, much more information.  And even with the additional information the error rate makes the test much too unreliable to provide a specific diagnosis of alcohol intoxication.  It is readily apparent why HGN is not generally an accepted test.  It is not conclusive, it is not specific, it is insensitive and the methodology that is commonly used has not been systematically validated.

In addition, without electronystagmography, the test itself and its interpretation can be “fudged”.  That is, it is subject to fraud.

Similar problems exist with the walk and turn test and the one leg stand test.

      Such examinations are not accepted in the medical scientific community.


[1] (Goldfrank’s Toxicological Emergencies, NE Flomenbaum, LR Goldfrank, RS Hoffman, NA Lewin, LS Nelson, MA Howland, 2006 pages 12, 1-16, 8th ed.