Casework drug and alcohol findings across our 29-parish service area, 2021 through October 2026, framed against current national impaired-driving recommendations (J. Analytical Toxicology).
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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.
Executive Summary
The signals that most define North Louisiana’s recent toxicology casework, recomputed from the data on every update. Figures are the share of that year’s cases; 2026 is partial (through October).
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. Analytical Toxicology. 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 to Tier I discussed in the Executive Summary, 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. Analytical Toxicology. 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. “No Assigned Tier” includes non-impairing/OTC and other substances tracked locally but not on the recommended impaired-driving scope.
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.
Blood alcohol distribution (alcohol-positive cases)
Bins line up with the 0.08 and 0.15 g/dL thresholds. Light blue is below 0.08, orange is 0.08 to 0.149, and dark blue is 0.15 and above. Not-tested and negative cases are excluded.
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. 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
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.
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. Switch to Change between years to see where caseloads and the alcohol and drug mix are shifting. Hover or tap a parish for its breakdown.
ComparewithComplete years only. The Case Year filter above doesn’t apply in this view; the parish and agency filters do.
Antemortem case frequency by parish
Alcohol vs. drug profile, top parishes
All parishes (antemortem)
Analytes Detected
Every substance NLCL toxicologists reported, including metabolites, with how often it was found and its blood concentration range. Choose antemortem (driving) or postmortem casework, narrow the list by drug class, or search for a substance.
Postmortem sampling site:
Tier I 2025 Tier I scopeTier II 2025 Tier II scopeNo Assigned Tier not in the 2025 Tier I or Tier II scope
Reading postmortem concentrations. After death, many drugs move out of tissue stores into the blood (postmortem redistribution). Central blood from the heart, aorta or pleural cavity is usually affected most and can run considerably higher than peripheral blood for the same person. Peripheral (femoral or subclavian) blood is generally preferred for interpretation. Compare postmortem values only with postmortem values from the same site; they aren’t comparable to antemortem (driving) concentrations.
An analyte is the specific substance measured, so metabolites such as THC-COOH and benzoylecgonine are listed on their own. Each case counts once per analyte. Concentrations (ng/mL) use the highest value reported for each case at the selected site, which captures dilution re-analyses; qualitative results are excluded. With All cases or Antemortem selected, concentrations come from antemortem blood only. With Postmortem selected, pick a sampling site: “Any blood site” uses peripheral blood when it was tested, then unspecified blood, then central blood. Vitreous fluid, serum and oral fluid are not included in concentration statistics. Grey italic values rest on fewer than 10 results. Shading reflects the 2025 national recommendation tiers, not NLCL’s testing scope.
Delta-9 THC in Antemortem Blood
Delta-9 THC is the psychoactive parent compound in cannabis. THC-COOH and THC-OH are its metabolites. These figures use antemortem (living-driver) blood results only.
Postmortem sampling site:
Delta-9 THC concentration distribution
Grey is below 2 ng/mL, light blue is 2 to 4.9 ng/mL, and orange is 5 ng/mL and above. The 2025 recommended confirmation cutoff for delta-9 THC in blood is 1 ng/mL; 5 ng/mL is a threshold some states write into law.
Median concentration and share at or above 5 ng/mL, by year
2026 is partial.
Cannabis-positive drivers: delta-9 THC present vs. metabolite only
“Metabolite only” means THC-COOH or THC-OH was found without delta-9 THC, a pattern usually associated with use further in the past.
Postmortem THC. THC is highly fat-soluble, so its blood concentration after death can shift with the sampling site and the interval before collection. Central blood often reads higher than femoral blood. Postmortem values describe exposure before death. They shouldn’t be compared with driving-case concentrations or with per se driving limits.
How to read THC numbers. Unlike alcohol, blood THC concentration is a poor indicator of impairment. THC falls quickly after use, often within a few hours, while its effects can last longer, and frequent users can carry measurable THC without recent use. No single concentration separates impaired from unimpaired drivers, so these figures describe exposure, not impairment.
Drug Classes & Polydrug Use
How many drugs each case contained, and how each drug class has trended as a share of cases. Drug counts use the same rules as the rest of the dashboard: metabolites collapse into their parent drug, and nicotine and naloxone are not counted.
Drugs per case, by year
Bars show the share of each year’s cases by number of drugs detected (alcohol not counted). The black line is the average number of drugs among drug-positive cases. 2026 is partial.
Drug class trends: what’s rising and what’s falling
Share of all cases involving each class. Click any class to enlarge it and see the individual drugs behind the trend.
A case counts once per class. Each headline compares the first year with at least 100 cases in the selection against the latest complete year; a change of at least one percentage point counts as rising or falling. Classes with fewer than 15 cases overall are not shown. Each chart has its own vertical scale, so compare the percentages rather than the line heights.
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).
How North Louisiana Compares to the National Picture
Benchmarked against a large national impaired-driving cohort (Cieri et al., J. Analytical Toxicology 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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