Letter from Dr. Bob to Rep. Claire Levy

From: Dr. Robert J. Melamede, Ph.D.
Cannabis Science Inc
6946 N Academy Blvd, Suite B #254
Colorado Springs CO 80918

To: Rep. Claire Levy

Dec. 20, 2010

In recognition of Colorado state's regulatory efforts to balance the need to protect it's citizens from impaired drivers, with an appropriate science-based protection of basic rights of the states medical marihuana patients, I am providing you with some peer reviews scientific articles that I hope will shape your views especially with regard to the 5ng/ml plasma THC level under consideration.

As you can readily see in table 2 of the attached article (the relevant portion shown below), the plasma THC concentration in the baseline control subjects (consisting of heavy cannabis users with an average age of 23.2 years) was already well above proposed limit for determining impairment.

Furthermore, the author's conclusions based on performance tests, were fully consistent with previous studies that demonstrated limited impairment caused by THC in regular cannabis users.

"Previous research has demonstrated that daily cannabis users are less sensitive to the impairing effects of Delta-9-tetrahydrocannabinol (THC) intoxication on cognitive and psychomotor functions (D'Souza et al. 2008; Hart et al. 2001; Jones et al. 1981; Ramaekers et al. 2009) that have often been demonstrated in occasional cannabis smokers (Curran et al. 2002; Hart et al. 2002; Heishman et al. 1989; Lamers and Ramaekers 2001; Ramaekers et al. 2004; Ramaekers et al. 2006a), even when THC concentrations and levels of subjective high are similar (Ramaekers et al. 2009). This loss of sensitivity or tolerance to the behavioral effects of THC after prolonged use is believed to result from a change in pharmacodynamic response as evinced by CB1 receptor downregulation in large parts of the brain (Gonzalez et al. 2005). Alternatively, it has also been suggested that heavy cannabis users recruit alternative neural networks as a compensatory mechanism during task performance. Eldreth et al. (2004) and Kanayama et al. (2004) showed that compared with controls, cannabis users utilized additional brain regions to perform cognitive tasks, i.e., they compensated by working harder and recruiting compensatory networks."

The authors further concluded:

"THC did not affect performance of heavy cannabis users in the critical tracking task, the stop-signal task, and the Tower of London. These tasks have previously been shown to be very sensitive to the impairing potential of THC when administered to infrequent cannabis (Ramaekers et al. 2006a)."

They also noted:

"However it was interesting to note that tolerance was not apparent in all performance tasks. During divided- attention task performance, THC increased the number of control losses and reaction time and decreased the number of correct signal detections. Number of times that subjects lost control over the primary task (tracking) during this dual task performance appeared particularly sensitive to the impairing effect of THC." It is worth noting that sleep deprived subjects also show performance deficits in this task.

In view of the above data, the proposed regulatory plasma limit would unfairly single out sick medical marijuana patients as being impaired through the use of criteria that were inappropriate for this population. Furthermore, infrequent users will tend to have lower THC concentrations while being more impaired, thus defeating the very purpose of the regulations. In view of the above peer reviewed science, setting inappropriate THC plasma levels would needlessly harm patients and burden the judicial system.

It would make a lot of sense to test for both THC and alcohol to determine impairment. The 5 ng/ml would probably make sense when determined in conjunction with the alcohol level.

I have also attached an study that examined marijuana as a potential causative agent for automobile accidents in Colorado. The authors concluded "Alcohol remains the dominant drug associated with injury- producing traffic crashes. Marijuana is often detected, but in the absence of alcohol, it is not associated with crash responsibility."

Thank you for your consideration,

Dr. Robert J. Melamede


Ramaekers, J. G. et al. Tolerance and cross-tolerance to neurocognitive effects of THC and alcohol in heavy cannabis users. Psychopharmacology (Berl) (2010).

Lowenstein, S. R. & Koziol-McLain, J. Drugs and traffic crash responsibility: a study of injured motorists in Colorado. J Trauma 50, 313-320 (2001).