Casework drug and alcohol findings across our 29-parish service area, 2021–2026, framed against current national impaired-driving recommendations (J Anal Toxicol).
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About this data. These figures come from cases submitted to NLCL for testing. They reflect what agencies send us and our testing scope, so they are not a measure of drug use in the general population. NLCL tests for drugs regardless of alcohol level and does not use stop-limit testing. Postmortem and antemortem cases are tracked separately. Small parish-level counts are suppressed to protect privacy. Years shown as partial (2026) are not used for year-over-year growth.
Service-Area Overview
A baseline snapshot of NLCL casework. Use the tabs above to explore how local findings line up with the 2025 national testing recommendations.
Cases per year
2026 is a partial year.
Alcohol result categories (all cases)
Most frequently detected substances
About These Results
This dashboard presents North Louisiana Criminalistics Laboratory (NLCL) casework. Its structure and benchmarks draw on two peer-reviewed studies from the Journal of Analytical Toxicology. Those papers shaped how we organize and interpret the data; the numbers shown here are entirely NLCL’s own.
1. National testing recommendations (the framework)
D’Orazio AL, Mohr ALA, Chan-Hosokawa A, Harper C, Huestis MA, Kerrigan S, Limoges JF, Miles AK, Scarneo CE, Scott KS, Logan BK. Recommendations for toxicological investigation of drug-impaired driving and motor vehicle fatalities—2025 update.J Anal Toxicol. 2026;50(1):bkaf085. doi:10.1093/jat/bkaf085.
This consensus update defines the Tier I and Tier II drug scopes that labs are encouraged to test for in impaired-driving cases. It informs our National Recs Scope tab (which drugs map to which tier), the gabapentin promotion highlighted in the Drug Spotlight, and the alcohol stop-limit concern explored in the Stop-Limit Effect tab.
Cieri G, Mohr ALA, Fogarty M, Chan-Hosokawa A, Logan BK. Four-year evaluation of drug-impaired driving drug concentrations.J Anal Toxicol. 2024;48(9):641–652. doi:10.1093/jat/bkae073.
This study reports drug positivity and blood concentration statistics from a large national impaired-driving cohort (~70,000 cases, 2017–2020). It is the national yardstick behind our National Benchmark tab, where NLCL’s antemortem blood medians are compared, drug by drug, against the national medians.
These figures come from cases submitted to NLCL for testing. They reflect what agencies send us and our testing scope, so they are not a measure of drug use in the general population. NLCL does not practice alcohol stop-limit testing. We test for drugs regardless of a case’s alcohol concentration, so our drug findings are never truncated by an alcohol threshold. Postmortem and antemortem cases are tracked separately, and benchmark comparisons use antemortem blood only to match the national study. These results exclude urine samples submitted to the laboratory over this period; every specimen type analyzed here is blood or a blood subtype (femoral, cardiac, aorta, pleural, peripheral, subclavian, and so on), plus a small handful of non-urine alternatives (vitreous fluid, oral fluid, and serum). Partial years (2026) are excluded from year-over-year growth. Questions about methodology may be directed to NLCL at nlcl.org.
North Louisiana vs. the 2025 National Recommendations
The 2025 update sorts the most relevant impaired-driving drugs into a Tier I scope (highest national prevalence) and a Tier II scope. Here is how often each substance actually shows up in NLCL casework, with its national tier.
What changed in 2025: Gabapentin was promoted to Tier I. Carisoprodol and meprobamate were demoted to Tier II. Urine was removed as a recommended matrix for impaired-driving drug testing.
Detected substances by national tier
Tier assignments per D’Orazio et al. 2025. “Not on 2025 menu” includes non-impairing/OTC and other substances tracked locally but not on the recommended impaired-driving scope.
Drug Spotlight
A rotating deep dive on one substance. Default is gabapentin, the drug the national panel just elevated to Tier I. Switch drugs with the menu.
Detections per year
2026 partial.
Antemortem vs. postmortem
Most common co-detected substances
Among cases where the spotlight substance was detected.
The Stop-Limit Effect
The 2025 update flags alcohol “stop-limit” testing, where a lab stops drug testing once alcohol is at or above a set level, as a practice that hides the true scope of drugged driving. NLCL does not use stop-limit testing; we test every case regardless of alcohol concentration. Because we do, the drug findings below were caught. The figures show, hypothetically, how many of these same NLCL cases a stop-limit lab would have missed.
If testing stopped at 0.08 BAC
Drug-positive driving cases missed, by stop-limit
Hypothetical illustration only; NLCL does not practice stop-limit testing. Denominator: all antemortem drug-positive cases (n=1137). A case counts as “missed” when its measured BAC is at or above the stop-limit, meaning a stop-limit lab would not have performed drug testing on it.
Alcohol Concentration Trends
A closer look at the alcohol-positive cases in NLCL casework: how blood alcohol concentrations are distributed, how often other drugs appear alongside alcohol at each level, and how these patterns have moved over time.
A counterintuitive but consistent pattern. As blood alcohol climbs, the share of cases that also contain drugs falls: from 69% below 0.08, to 63% at 0.08–0.149, to 56% at 0.15 and above. The lower-alcohol impaired-driving cases are the ones most likely to involve additional drugs, which is exactly where drug testing adds the most. This trend is statistically significant and holds regardless of case type.
Drug co-detection by alcohol level (alcohol-positive cases)
“Avg. drugs (when present)” counts adjusted drug exposures (parent drugs, metabolites collapsed, alcohol not counted) among only the cases that actually contain drugs. That figure stays close to 1.8 at every alcohol level — so what changes as alcohol rises is the likelihood of any drugs being present, not how many are present once they are.
Drug co-detection & drug burden by alcohol level
Median blood alcohol among positive cases, by year
Median BAC among alcohol-positive cases has eased from 0.171 (2021) toward ~0.14 in recent years. 2026 is partial.
Alcohol-positive cases over time: alcohol alone vs. alcohol with drugs
Across the period, most alcohol-positive cases also involved one or more drugs (1,047 alcohol-positive cases overall; 636, or 61%, also drug-positive).
Parish Map — Antemortem (DUI/DUID) Cases
Antemortem casework only (the living-driver, impaired-driving population), mapped by the submitting parish. Postmortem cases are excluded here. Hover or tap a parish for its breakdown.
1,325 antemortem cases map to 25 Louisiana parishes, with Caddo (481) and Ouachita (369) accounting for the largest shares. A further 427 antemortem cases came in statewide (Louisiana State Police, no single parish specified) and 10 from outside Louisiana; both groups are listed below the map but not shaded on it.
Antemortem case frequency by parish
Alcohol vs. drug profile, top parishes
Each bar is one parish’s antemortem cases, split into alcohol only, alcohol + drugs, drugs only, and neither detected.
All parishes (antemortem)
“% of AM” = share of all 1,762 antemortem cases. Statewide (no parish) and out-of-state rows are shown for completeness.
Combinations & Emerging Threats
Polysubstance findings and substances that are newly appearing or growing fast. Intelligence value for traffic-safety and law-enforcement partners.
Most common substance combinations
Pairs counted per case; alcohol included as a combination partner.
Emerging & fast-growing substances
“New” = first detected in 2023 or later. Growth compares 2021 to 2025 (complete years).
Worth noting: xylazine, an emerging adulterant nationally, has not yet been detected in NLCL casework through this dataset. Absence is itself useful surveillance intelligence, and a candidate to add to routine scope for early warning.
How North Louisiana Compares to the National Picture
Benchmarked against a large national impaired-driving cohort (Cieri et al., J Anal Toxicol 2024, ~70,000 NMS Labs DUID cases, 2017–2020). To keep the comparison fair, NLCL figures here use antemortem blood cases only, matching the national study’s matrix and case type.
The headline: NLCL’s cannabinoid and benzodiazepine median concentrations land almost exactly on the national medians, an external check that our analytical results are in line with a major reference laboratory. Stimulants (amphetamine, cocaine) and oxycodone run measurably higher locally, a real regional signal.
Median blood concentration: NLCL vs. national (ng/mL)
Ratio = NLCL median ÷ national median. Black ≈ on par with national (0.85–1.15x); orange = elevated locally; grey = below national. Drugs with very small local samples (n<20, marked) should be read with caution. Gabapentin is omitted here because it was not a national Tier I drug during the 2017–2020 benchmark period.
National positivity reference points
Measure (national, 2017–2020)
Value
Cannabis (delta-9 THC) positivity
46–49% of cases
Ethanol positivity
53–61% of cases
Fentanyl positivity
1.9% → 12%
Methamphetamine positivity
8.8% → 18%
THC + alcohol (top combination)
~19% every year
The national #1 combination, THC + alcohol, is also NLCL’s #1 combination (see Combinations tab). Different region, same leading pattern.
NLCL median concentration over time
Antemortem blood medians by year. Annual sample sizes are modest, so single-year swings are expected; read the multi-year shape, not point-to-point jumps. Nationally, fentanyl and methamphetamine medians rose steadily across 2017–2020.
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