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| Drug DUI and Cannabis |
What are the effects of THC on the brain of a driver?
DUI and cannabis information needs to be shared. For both DUI attorneys and medical experts in the courts, this is a concept known as THC Kinetics and involves the concept of Hysteresis. Recently I attended a seminar that covered key issues, Questions and Answers on Drug DUI with Dr. Stefan Rose of University Medical & Forensic Consultants, Inc. We learned that during the time of smoking marijuana and during the intoxication period (if one occurs) the blood and brain THC concentrations are in disequilibrium with each other. Another term for disequilibrium is “counterclockwise hysteresis”. When the THC blood levels are high the intoxication is low. When the THC blood levels are low, the intoxication (if present) is high, but only for a short time (minutes to an hour or so). Therefore it is IMPOSSIBLE to predict any pharmacologic effect at any point in time based on a blood THC test result. Nevertheless, there are harsh sanctions / penalties for refusing to take a test, when asked.
What is the scientific basis for urine testing and prediction of impairment by a driver?
NHTSA addresses Urine THC Kinetics in Drugs and Human Performance Study. With respect to Interpretation of Urine Test Results: Detection of total THC metabolites in urine, primarily THC-COOH-glucuronide, only indicates prior THC exposure. Detection time is well past the window of intoxication and impairment.
What do controlled clinical studies tell us about DUI and drug impacts on THC Cannabis impairment?
Published excretion data from controlled clinical studies may provide a reference for evaluating urine cannabinoid concentrations; however, these data are generally reflective of occasional marijuana use rather than heavy, chronic marijuana exposure. It can take as long as 4 hours for THC-COOH to appear in the urine at concentrations sufficient to trigger an immunoassay (at 50ng/mL) following smoking. Positive test results generally indicate use within 1-3 days; however, the detection window could be significantly longer following heavy, chronic, use. Following single doses of Marinol®, low levels of dronabinol (same as THC) metabolites are present for more than 5 weeks in urine. Low concentrations of THC have also been measured in over-the-counter hemp oil products – consumption of these products may produce positive urine cannabinoid test results.
What do we know about drug driving and THC Kinetics?
1. When smoking marijuana, THC is rapidly absorbed into the bloodstream from the alveoli in the lungs
2. The peak blood THC concentration occurs within minutes near or after the end of smoking
3. The THC goes through the blood to the organs and tissues of the body
4. As the blood THC concentration is falling the brain THC concentration is rising (hysteresis) therefore NO correlation of blood THC concentration to intoxication exists
5. The blood flow–peak determines the time to reach maximum THC concentrations in the various organs and tissues. The organs with the most blood flow have THC concentration the quickest
6. The organs with the highest blood flow are the brain, liver, kidneys and lungs
7. Skeletal muscle has low blood flow and fat tissue has very low blood flow
8. Fat accumulates THC slowly, and releases THC back into the bloodstream for days, weeks and months after the last dose of THC
9. Chronic marijuana users may have measurable residual THC levels in the blood for days and weeks after the last dose
10. A single blood THC result cannot determine when a person smoked marijuana or how much marijuana a person smoked!
11. A single blood THC result by itself cannot determine a person’s impairment from THC. Clinical correlation is necessary!
Can a THC Result Can ever Predict Impairment?
1. THC Blood : Serum ratio not known (if sample is serum)
2. THC Kinetic curve unknown (THC at driving not known)
3. THC Hysteresis effect not known
4. Residual THC in blood not known
5. THC drug-dose response not known
6. THCt olerance not known
7. CBD content and effect not known
8. Neurologic exam for THC effect not performed
9. Even NHTSA says it cannot be done!
How can a lawyer and an expert Challenge Blood Drug Results?
1. Challenge the chemical analysis for quantitative and qualitative accuracy. The quantitative value ALWAYS has error and uncertainty associated with it. Challenge the quantitative value through the ISO 17025 standard. Inspect ALL documents from the Laboratory Litigation Package and look for qualitative errors. A successful challenge to a driver’s license suspension can avoid a suspension.
2. Challenge the idea that a single blood drug test predicts blood drug concentration at the time of stop or crash. Blood drug concentrations are a moving target, and constantly changing. Therefore blood drug concentrations at the time of a stop or crash are unpredictable with a single blood drug test result. In fact, the only way to know the blood drug concentration is to have a blood sample taken at the time of the stop or crash
3. A blood drug concentration can NEVER predict the pharmacologic effect, or impairment on any individual even with known blood drug concentration! Pharmacology studies include populations of people, and those studies do not predict the pharmacologic effect on any individual because of the wide range of response to any drug. Modern medical pharmacology holds that doctrine to be true and cannot be changed for the sake of litigation. Counter-clockwise hysteresis of THC makes the prediction of impairment from a blood THC result IMPOSSIBLE.
What are important cross examination questions to ask in Drug DUI cases?
1. What type sample was analyzed? Whole blood, serum, plasma?
2. If serum/plasma, what was the whole blood: serum THC ratio?
3. What sample type are you referring to regarding any study of pharmaco-kinetics/pharmaco-dynamics?
4. Have you made the necessary correction in your calculations if the sample type is different?
5. How do you know what the defendant blood: serum THC ratio was?
6. What is the target organ that THC affects? (BRAIN)
7. What is the BRAIN THC concentration that causes impairment?
8. Was the BRAIN THC concentration measured?
9. A low blood THC concentration can mean a high or low brain concentration, correct?
10. Blood THC concentration does not predict BRAIN THC, does it?
11. How do you know what the defendant’s BRAIN THC concentration was?
12. Even if you knew the BRAIN THC concentration you would not know if that caused impairment, would you?
13. There is no published correlation between blood THC, BRAIN THC and impairment, is there?
If you need a forensic consult on your case please contact Dr. Stefan Rose directly by email at toxdoc@umfc.com or call 561-795-4452. Questions and Answers from recent Class on Drug DUI with Dr. Stefan Rose. University Medical & Forensic Consultants, Inc. ©2015.
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