Expert Witness Blog
Toxicology Expert Witness John P. Bederka, Ph.D. of TOXICULL Associates writes in his article about the need for businesses, governments, legal entities, and scientists to effectively evaluate the increasing prevalence of marijuana use. He poses and analyzes many questions in the article, including the following:
1. Is there any relationships between blood THC v. brain THC?
2.How does the percent THC in the smoked marijuana cigarette relate to blood levels of THC in the user?
3.How does the blood level of THC relate to the perception of “high” in the user?
4. Is the practiced/heavy marijuana user just one end of the scale for dose response effects?
5. Is the blood level of THC the only cannabinoid of interest in evaluating behavioral effects in the user?
6.Is urine testing for cannabinoids of any either clinical or evidentiary value?
7. Impairment & marijuana: laboratory and on-road considerations.
Among his conclusions are the following:
1. Scientific literature reports on practiced marijuana users afford analytical and clinical data that totally disallow the definitive estimation of time since last use, and, any degree of any impairment based upon current drug testing methods.
2. THCCOOH has no part to play in any attempt to determine time of use of marijuana since the half lives in plasma or urine are in the ranges of days to weeks respectively.
3. Given that THCCOOH is not psychoactive, neither plasma nor urine THCCOOH levels have any utility in assessing “degree of impairment.”
4. Urine THC levels have been found to peak at about two hours post smoking, and urine HydroxyTHC peaks at about three hours post smoking. Thus, a ratio of Hydroxy THC to THC
levels of greater than two allows that the timeofuse was less than about three hours.
5. Higher percentage amounts of THC in the available marijuana have not significantly increased plasma THC levels in users, and, therefore, cause no probable change in currently acknowledged marijuana associated behaviors. It remains to be seen if increased levels of THC
in the available marijuana will, in fact, lead to less total marijuana smoking as is suggested by anecdotal evidence.
6. The perception of the “degree o f high” is not directly related to a plasma level of THC.
7. The signs and symptoms associated with marijuana use are unique to the individual user, and are not defined/determined by blood levels of any cannabinoids.
8. When cognitive and/or psychomotor impairment was reported to have occurred, such effects were usually found within one hour of beginning the individual marijuanasmoking event.
9. Socalled standardized field sobriety tests (SFSTs) in alleged marijuana exposed individuals have, at best, a 30 to 50 percent probability of indicating some degree of impairment,
and are a function of set and setting.
10. Plasma THC levels of above 30 ng/ml would allow that the occasional smoker could have been exposed to marijuana smoke within about the previous hour and the practiced smoker within about two hours.
11. The above afforded data and available comparative considerations of psychomotor functionality allow that the practiced/heavy marijuana smoker is no more impaired, and either a danger to self or society than that of the committed social drinker and may be similar to the practiced coffee drinker, committed aspirin, valium, and/or nonsteroidal anti inflammatory drug treated patients.
12. The sum and substance of the foregoing is that no blood level of any cannabinoid is objectively defensible as a measure of any degree of impairment in the individual smoker.
13. The proposed blood THC level of five ng/ml as the legal/illegal marker for the probable marijuana related criminalization of the individual has no scientific legs.
The full article can be read here: Marijuana Impaired, or, Just Cannabinoid Positive?