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Evaluation of Drug Recognition Expert Reports in Marijuana Cases

A study assessing DRE indicators for cannabis in cases with THC detection, comparing indicators for subjects with active THC versus THC-COOH only. The study analyzes various indicators such as pupil size, pulse rate, blood pressure, and lack of convergence. Results show that DRE matrix is a useful tool for predicting marijuana use, with similar indicators for THC/THC-COOH and THC-COOH only cases. However, the short half-life and long examination process pose challenges. This research aligns with the findings of a related study on predictors of drug use.

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Evaluation of Drug Recognition Expert Reports in Marijuana Cases

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  1. Evaluation of Drug Recognition Expert Reports in Marijuana Cases Brianna Peterson, Ph.D. and Rod Gullberg, M.S. Washington State Patrol September 20, 2011

  2. Goal of study • Determine if DRE indicators for cannabis are present in cases with THC detected • Compare indicators for subjects with active THC versus THC-COOH only

  3. DRE Matrix Dissociative Anesthetics Inhalants Cannabis Stimulants Hallucinogens Narcotic Depressants Analgesics Horizontal Gaze Nystagmus Present Present Present None None None None Vertical Gaze Nystagmus Present Present Present None None None None Present Present Present Present None None None Lack of Convergence Normal Normal Normal Dilated Dilated Dilated Constricted Pupil size Slow Slow Normal Normal Slow Normal Little to Reaction to light none Down Up Up Up Up Up Down Pulse Down Up/Down Up Up Up Up Down Blood Pressure Normal Up/Down Up Normal Up Up Down Body Temp /Normal

  4. DRE indicators for cannabis category • Lack of convergence (LOC) present • Pupil size normal to dilated • Elevated pulse rate • Elevated blood pressure • Horizontal gaze nystagmus (HGN) not present • Vertical nystagmus (VGN) not present • Reaction to light is normal • Body temperature is normal

  5. THC pharmacokinetics • Highly lipid soluble • Short half-life • 3 hrs post smoking, THC in serum <5 ng/mL • Main metabolite: 11-nor-9 carboxy-THC (THC-COOH)

  6. Methodology • DRE cases from 2007-2009; blood sample analyzed • Tested for volatiles by Headspace Gas Chromatography • EMIT drug screen • Cannabinoids cut off = 10 ng/mL THC-COOH • THC confirmation by GC/MS (SIM mode) • Limits of Detection • THC = 1.0 ng/mL • THC-COOH = 5.0 ng/mL Cases that were only positive for THC or THC-COOH

  7. Subjects • THC/THC-COOH (n=101) • 93% male • 78% Caucasian • Average age: 24 (range: 16-70) • THC-COOH only (n=147) • 79% male • 84% Caucasian • Average age: 27 (range: 14-61) • Not impaired (n=17) • 76% male • 94% caucasian • Average age: 38 (range: 19-74)

  8. Results 147 THC/THC-COOH cases Mean = 7.3; median = 5.7 Mean = 74.1; median = 61.7 101 THC-COOH only cases Mean = 16.6; median = 13.5

  9. Lack of convergence *p=0.003 *p=0.003 *p=0.003

  10. Average pupil size: Room light Normal range: 2.5 – 5.0 mm 56%, 61% above normal range

  11. Average pupil size: Dark Normal range: 5.0 - 8.5 mm 60%, 58% above normal range

  12. Average pupil size: Direct light Normal range: 2.0 – 4.5 mm 49%, 47% above normal range

  13. Average pulse Normal range = 60-90 bpm 57% above normal range

  14. Systolic blood pressure Normal range = 120 – 140 mm Hg 45% above normal range

  15. Body Temperature Normal range = 98.6 ± 1°F 73, 87% in normal range

  16. Summary Cannabis THC/THC - THC - Not indicator COOH COOH impaired HGN None 9% 11% 6% VGN None 0 2% 0 Lack of convergence Present 66% 47% 6% Pupil Size Normal to 55% 55% 15% dilated Reaction to light Normal 76% 77% 82% Pulse Elevated 57% 57% 25% Blood pressure (Systolic/diastolic) Elevated 45%/22% 45%/25% 41%/12% Body Temperature Normal 73% 87% 77% Not impaired: 17 cases from 2007 - 2009

  17. Summary THC/THC - THC - COOH Not COOH impaired Bloodshot eyes 86% 81% 24% Eyelid tremors 81% 81% 38% 2/8 clues on WAT 72% 81% 25% 2/4 clues on OLS 46% 57% 31%

  18. Other indicators • Romberg test: estimation of 30 seconds • Normal range = 25 to 35 seconds

  19. Other indicators • Rebound Dilation • Reaction to light • Normal, slow, little

  20. DRE Opinion • THC/THC-COOH cases • 97% DRE called cannabis • Other cases called ‘not impaired’ • 98% subject admitted to marijuana use • THC-COOH only cases • 97% DRE called cannabis • Stimulant/not impaired • 88% subject admitted to marijuana use

  21. Conclusions • DRE matrix is useful tool for predicting marijuana use • Similar indicators for THC/THC-COOH and THC-COOH cases • Short half-life, long exam process

  22. Beasley et al. study • Examined which indicators best predict substance (n =742) • Stimulants versus cannabis • Stimulants: less reddening of eyes and rebound dilation, more likely to have hippus, injection sites, slow reaction to light • Cannabis: more likely to have lack of convergence Toward a More Parsimonious Approach to Drug Recognition Expert Evaluations. Traffic Injury Prevention 2009;10:513-518

  23. Acknowledgments • Rod Gullberg • Research Analyst, Washington State Patrol

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