North Carolina Drug DWI | North Carolina Drugged Driving Charges

Drug-based DWI prosecutions in North Carolina operate under an evidentiary framework that differs substantially from alcohol enforcement. In DUI cases involving drugs (sometimes called DUID – driving under the influence of drugs) or “drugged driving” by the general public, the forensic analysis and legal issues tend to be significantly more complex.  

Unlike alcohol, for which decades of research have provided relatively clear thresholds (like 0.08 BAC) and relatively well-understood pharmacology, psychoactive drugs present a diverse and evolving challenge. 

Alcohol impairment is supported by decades of controlled laboratory research, standardized psychomotor testing models, and population-level epidemiology that correlate rising blood alcohol concentrations with relatively predictable losses of cognitive and motor functioning at certain BAC levels.

Those studies informed legislative adoption of per se thresholds such as 0.08 BAC. Drug impairment has no comparable scientific consensus. When blood is drawn in suspected drug-related DWI investigations, forensic laboratories follow a multi-stage analytical process that produces chemical detection data but not impairment determinations.

Psychoactive drugs vary dramatically in chemical structure, absorption methods, metabolism rates, duration of effect, and behavioral impact. No uniform impairment curve exists across drug classes, and even within a single drug, blood concentration correlates poorly with actual functional impairment between different people or even across repeated dosing in the same person.

DUI defense attorneys, therefore, must contend not only with the science of toxicology but also with the occasional lack of consensus on what drug levels constitute impairment. DWI defense and “Drugged Driving” Lawyers at Powers Law Firm help clients navigate the technical complexities of toxicology evidence. If you’re facing drug-related DWI charges, call or TEXT 704-342-4357 for a confidential case evaluation.

Screening Drug Impairment Blood Samples

When a blood sample is tested for drugs, labs typically employ screening and confirmation processes.

In a common workflow, an initial immunoassay screen flags classes of drugs ( opiates, cannabinoids, benzodiazepines) followed by a confirmatory test using Gas Chromatography-Mass Spectrometry (GC/MS) or Liquid Chromatography-Tandem Mass Spectrometry (LC-MS/MS) for specific drugs and their metabolites.

The confirmatory tests can quantify the amount of the drug in the blood. The results might show, for example, a THC level in ng/mL, or a certain concentration of alprazolam, etc.

However, what do those numbers mean for impairment? That’s the crux of the issue.

Blood testing for drug-impaired driving is usually performed via immunoassay testing. These tests identify drug classes rather than specific compounds.

Common screened groups include cannabinoids, opiates, benzodiazepines, amphetamines, barbiturates, antidepressants, and synthetic opioids.

Immunoassays are designed to be sensitive rather than selective. They intentionally err toward false positives to avoid missing potentially positive specimens.

Cross-reactivity is an acknowledged limitation. Structurally similar (in molecular composition) substances may trigger reactions unrelated to illegal or impairing drug use.

Examples may include things like:

• Poppy seed ingestion occasionally triggers opiate screens.
• Over-the-counter cold medications containing pseudoephedrine (“Sudafed”) cross-react with amphetamine assays.
• Certain antidepressants cross-react with benzodiazepine assays.
• CBD products trigger cannabinoid presumptive positives at low thresholds.

At this stage, forensic conclusions drawn regarding specific substances or impairment are problematic at best.

A screening result merely indicates the possibility that a substance within a broad category may be present, meriting more and better testing protocols using more sensitive and reliable machinery. 

Confirmational Testing of DUI Drug Cases 

Confirmatory testing should follow any positive screen before identification is considered scientifically reliable.

In North Carolina, this ordinarily involves Gas Chromatography-Mass Spectrometry (GC/MS). The technology allows for:

• Identification of specific parent drugs and metabolites.
• Quantification of substances in blood using concentrations measured in nanograms per milliliter (ng/mL).
• Differentiation between psychoactive compounds and non-active metabolites.

The final lab report typically lists the detected drug compounds, their concentrations, and reference information on detection thresholds.

What these numeric results do not establish is impairment at any particular time.

Drug DWI Evidence in North Carolina at a Glance

Evidence Type	What It Shows
Blood Drug Test (GC/MS)	Presence and concentration of a drug or metabolite at the time of blood draw
Immunoassay Screen	Possible presence of a broad drug class such as cannabinoids, opiates, or benzodiazepines
Field Sobriety Tests	Observed performance on divided-attention and balance tasks
Officer Observations	Driving conduct, speech patterns, coordination, pupil size, and demeanor
DRE Evaluation	Structured observational assessment suggesting possible drug categories
Blood Collection Timing	The time the blood sample was drawn relative to the stop or crash
Metabolite Detection	Evidence of prior exposure to a drug
Schedule I Drug Detection	Any amount of a Schedule I substance or its metabolites in blood or urine

Relationship Between Blood Concentration and Impairment

Unlike blood testing for alcohol impairment, the relationship between blood drug concentration and impairment is not always linear nor predictable. Several factors drive this disconnect.

Regular users of a drug may function surprisingly well at blood levels that would debilitate a first-time (“naïve”)user. A chronic opioid user might appear normal at a blood morphine concentration that would knock out a non-user. Similarly, heavy cannabis users can have high THC residual levels long after last use without acute impairment.

1. Tolerance

   Regular users of certain substances may develop pharmacodynamic tolerance, meaning higher concentrations are required before observable impairment appears. Common examples can include:

• Chronic opioid users are functioning at morphine or oxycodone concentrations that would incapacitate an opioid-naïve person.
• Regular cannabis users maintain baseline THC blood levels while performing daily tasks without observable impairment.
• Long-term benzodiazepine patients demonstrate compensatory functioning at doses that sedate first-time users.

Tolerance means that identical drug concentrations in two individuals do not equate to comparable levels of cognitive or motor impairment.

2. Pharmacokinetics and Timing

Many drugs have metabolites (breakdown products) that can linger in the blood after the active effect has worn off.

For example, carboxy-THC can be detected days after marijuana use, but it may be inactive (non-impairing). Even active THC can remain detectable at low levels for several hours, long after peak impairment (which usually occurs within 1-2 hours of smoking).

Thus, a blood test might catch the presence of a drug without the presence of impairment. Most psychoactive drugs demonstrate rapid absorption followed by rapid redistribution into tissues. Peak impairment seldom aligns with peak blood concentration. For example:

• Smoked cannabis often produces peak subjective impairment within thirty to sixty minutes, while blood THC concentrations may drop sharply within two hours due to redistribution into fat tissue.
• Active THC metabolites and inactive carboxy-THC remain detectable for extended periods after psychoactive effects have dissipated.
• Benzodiazepines may show stable blood concentrations while subjective impairment fluctuates based on circadian rhythms and cumulative dosing effects.

Consequently, detection of a substance at the time of blood draw does not establish impairment at the time of driving.

3. Metabolites Versus Active Compounds

Some drug detections involve metabolites rather than parent compounds. Certain metabolites retain psychoactivity while others do not:

• Delta-9-THC is psychoactive.
• Carboxy-THC is not psychoactive, yet can remain detectable for days.
• Diazepam metabolites may show activity, while others indicate past use only.

Failure to distinguish metabolite significance is common in court presentations and leads to exaggerated claims of impairment unsupported by pharmacology.

4. Absence of Numerical Thresholds

Except for a few exceptions, there is no universally accepted “legal limit” for drugs akin to 0.08 for alcohol. Some states have enacted per se limits for certain drugs (particularly marijuana in the wake of legalization). Others have a 5 ng/mL of THC per se limit and still others have 2 ng/mL or 1 ng/mL, etc.​

One defendant could be above 5 ng/mL THC shortly after use and be impaired, but another person might be above 5 ng/mL the next morning and not be impaired, yet both could be “per se” guilty in some states. Conversely, someone could be clearly impaired by cannabis yet have a THC level below 5 ng (depending on timing and metabolism).

Overall, no broadly accepted impairment threshold exists for psychoactive drugs equivalent to 0.08 BAC.

Despite legislative experimentation in some states, THC  limits ranging from 1 ng/mL to 5 ng/mL were not derived from validated impairment models. Scientific consensus recognizes that:

• Individuals may be measurably impaired below these thresholds depending on timing and sensitivity.
• Individuals may be unimpaired above these thresholds due to tolerance or delayed sampling.

Thus, the so-called per se thresholds reflect legislative compromise rather than biological certainty.

5. Poly-Drug Interaction

More often than some might suspect, impairment comes from combinations of substances (alcohol plus prescription meds, multiple drugs, etc.).

A blood test may quantify each, but scientists have even less guidance on how to interpret the combined influence versus the sum of parts.

If a defendant had a little alcohol (below 0.08) plus some Xanax plus marijuana, none at high levels, is that impairing? Possibly yes due to synergy. It can become a battle of experts and observations.

As such, a fair number of DUID cases necessarily involve multiple substances:

• Alcohol combined with benzodiazepines.
• Opioids with muscle relaxants.
• Cannabis with prescription stimulants.

Synergistic drug effects may exist, but toxicology cannot quantify combined impairment using simple additive models. No laboratory method currently determines whether two or more low-level substances jointly produce impairment. Assessments instead rely on subjective behavioral observations combined with speculative expert interpretation.

From a defense perspective, challenging drug DWI charges may involve both attacking the testing process and the interpretation of results.

During testing, it’s relevant to ask:

Were the proper confirmation tests performed to avoid false positives? Labs sometimes see mix-ups or have issues (misidentification of a substance).

Did the lab confirm the drug with GC/MS, and didn’t rely on a mere strip test or immunoassay? Was there a cross-reaction (for example, poppy seeds showing as opiates, or CBD products causing low THC positives)?

Unlike alcohol, there often is no clear-cut relationship between the blood concentration of some drugs (both legal and illegal) and driving impairment.

Defending a drug-based DUI requires a nuanced approach. Defense lawyers, when appropriate, are called to scrutinize the laboratory process (as with alcohol) and then aggressively challenge the meaning of any drug concentrations found.

It can be helpful to relate it back to driving behavior. If the driving was not egregious or the field sobriety tests were marginal, it may be possible to point out the disconnect between that and the notion of someone being high on drugs. If the driving was bad but you have a low drug level, fatigue, or something else may have been the cause, not the small amount of drug

DWI Drug Testing Accuracy and Compliance Issues

As such, defense analysis of drug testing may involve careful review of:

• Blood collection protocols.
• Chain of custody documentation.
• Sample storage conditions and preservatives.
• Laboratory accreditation.
• Device maintenance records.
• Analytical validation protocols.
• Quality control sample logs.

Potential failures include:

• Improper sample storage, possibly leading to degradation.
• Inadequate confirmation testing.
• Documentation gaps in quality assurance.
• Contamination or mislabeling.
• Inappropriate interpretation of screening tests as proof.

Without proper confirmation testing, immunoassay screen results are scientifically insufficient to support drug identification or legal conclusions.

Frequently Asked Questions About Drug DWI in North Carolina

What does a positive drug blood test mean for a Drug DWI charge in North Carolina?

In North Carolina, a positive drug blood test means that a substance or metabolite was detected in your bloodstream. With one notable exception, that does not always serve as sufficient evidence to prove driving impairment under N.C.G.S. § 20-138.1. Unlike alcohol cases governed by per se BAC thresholds, North Carolina has no numerical impairment limit for drugs, including THC. Ordinarily, prosecutors must still prove that your physical or mental faculties were appreciably impaired at the time of driving. Toxicology results establish exposure only. For Schedule I controlled substances, any detected amount or metabolite satisfies the statutory element regardless of impairment evidence. That statutory language is problematic at best. Courts are called upon to rely on officer observations, driving behavior, field sobriety testing performance, and law enforcement opinions to establish impairment, not laboratory concentrations by themselves. A positive blood test confirms that a controlled substance or metabolite was detected, but legal consequences depend on the drug category involved. Toxicology numbers alone should not establish impairment.

Is there a THC legal limit like the 0.08 BAC rule in North Carolina?

North Carolina has no “per se” THC or drug-concentration limits for impairment. No numerical drug thresholds exist to replace behavioral proof of impairment in DWI prosecutions outside the Schedule I framework.  With regard to Schedule I drugs in North Carolina, the State needs only to prove the existence of either active components or non-active metabolites to prove a violation of the NC DWI law.  Whether that statutory provision is Constitutional, particularly when and if the accused is not in fact “appreciably impaired” and/or “under the influence” of an impairing substance, is subject to some level of debate.

Can prescription medications lead to a Drug DWI "Drugged Driving" charge even when taken as directed?

Prescription compliance does not bar a DWI charge in North Carolina if law enforcement alleges that medication use appreciably impaired driving ability under N.C.G.S. § 20-138.1. Substances most often implicated include benzodiazepines, opioids, muscle relaxants, sleep medications, antidepressants, and stimulants. Toxicology evidence may confirm the presence of a prescribed drug, but lawful use alone does not establish impairment. The State must still prove that the medication affected physical or mental faculties at the time of driving through behavioral evidence such as driving conduct, field sobriety testing, or officer observations, rather than relying on blood concentration numbers by themselves.

How long can THC remain in your system in North Carolina blood testing?

THC can remain detectable in blood for several hours after use and, in regular users, low levels may persist into the following day or longer due to storage in body fat and slow redistribution into the bloodstream. Non-psychoactive metabolites such as carboxy-THC can remain measurable well after any impairing effects have ended. A blood test taken hours after driving therefore may reflect prior cannabis exposure rather than active impairment at the time of vehicle operation, making detection alone a poor indicator of driving impairment under North Carolina standards.

Can low levels of multiple drugs be used to prove "Drugged Driving" in North Carolina?

In North Carolina prosecutions for “Drugged Driving” involving multiple substances, the State may argue that the combined effects of low drug concentrations produced appreciable impairment even when each substance alone appears insignificant. Toxicology, however, provides no validated quantitative method for converting mixed drug concentrations into a reliable measure of driving impairment. There is no accepted model to calculate how overlapping drug effects translate into functional driving deficits. As a result, these claims hinge almost entirely on officer observations, field sobriety testing interpretations, and opinion testimony rather than on any objective scientific measurement drawn from laboratory data.

Can you be charged with Drug DWI in North Carolina if the blood test only shows drug metabolites?

In North Carolina, most drug-based DWI charges still involve proof of appreciable impairment even when metabolites rather than active drugs are detected. Metabolites often reflect historical use rather than current intoxicating effects and may not indicate that a driver was impaired at the time of operation. For Schedule I controlled substances, the statutory framework allows prosecution based on any detected amount of a drug or its metabolites, regardless of whether the compound is psychoactive. For all other drugs, metabolite detection alone does not always establish appreciable impairment, and the State would be inclined to rely on behavioral evidence together with laboratory results, rather than laboratory findings alone.

Does a blood drug test prove when the drug was taken?

A blood drug test confirms that a substance or metabolite was present at the time of collection, but it does not, by itself, pinpoint when the drug was consumed relative to driving. Drug absorption, tissue redistribution, metabolism, tolerance, dosing history, and individual physiology vary significantly between people and between drug classes, limiting the precision of backward inference from a single concentration value. Toxicologists may offer general pharmacological timelines and estimated use windows based on known drug behavior, and North Carolina law allows impairment to be proven at “any relevant time after driving.” Even so, a specific blood concentration may not establish with certainty whether a drug was taken immediately before driving or earlier in the day. Laboratory results should therefore be interpreted alongside driving behavior, field sobriety testing, witness observations, and other evidence rather than treated as a standalone indicator of the timing or existence of impairment.

Does a negative blood test mean you cannot be charged with drug DWI?

A negative blood test does not prevent a drug-based DWI charge in North Carolina if law enforcement contends that impairment was observed through driving behavior, field sobriety testing, or officer testimony. Toxicology evidence is not legally required to prosecute impaired driving. An officer may offer opinion testimony that a driver appeared to be “appreciably impaired,” and the State can proceed based on behavioral evidence alone. The absence of laboratory confirmation, however, undermines the ability to connect alleged impairment to any specific intoxicating substance and weakens claims that chemical impairment caused the observed driving conduct.

Understanding Drug DWI Evidence in North Carolina

Drug-based DWI cases in North Carolina can involve toxicology, statutory law, and real-world driving behavior. Unlike alcohol enforcement, where long-established BAC thresholds allow prosecutors to proceed under a largely numeric model, drug impairment cases rarely provide that kind of simplicity. Most psychoactive substances lack validated impairment thresholds, and blood test results do not reliably correlate with functional driving ability. For many defendants, toxicology reports prove only prior exposure rather than impairment at the time of operation. The evidentiary burden typically remains behavioral. Officers must rely on driving patterns, standardized field sobriety testing, body-worn and dash camera recordings, and observational testimony to establish appreciable impairment. Laboratory analysis becomes a supporting tool rather than a determinative metric.

An important statutory exception exists for Schedule I controlled substances under N.C.G.S. § 20-138.1(a)(3). For those substances, including their metabolites, North Carolina law does not require proof of appreciable impairment. Any detected amount satisfies the statutory element of the offense. This presence-based prohibition stands in stark contrast with toxicological science (and common sense), which does not support equating metabolite detection with active impairment.

Although N.C.G.S. § 20-138.1(a)(3) authorizes a presence-based offense for Schedule I substances and their metabolites, at present, there is no published North Carolina appellate decision that has squarely resolved whether this strict-liability framework is constitutional when applied in the absence of proof of actual impairment. The issue raises substantial due process concerns because it criminalizes conduct without requiring a showing that the driver was impaired or presented a safety risk at the time of operation.

While the “drunk driving law” is routinely enforced in trial courts, the appellate courts have thus far not issued a definitive ruling addressing whether presence alone, including inactive metabolite detection, satisfies constitutional limits. North Carolina appellate courts have repeatedly upheld the statute, overall, is a lawful exercise of legislative authority. Consequently, the legal significance of a drug test result may vary substantially depending on the classification of the substance involved and the evidentiary theory pursued by the prosecution.

If you are confronting a drug-based DWI allegation, an informed case evaluation deserves far more than reviewing a single lab number. Testing protocols, confirmation compliance, metabolite interpretation, blood-draw timing, tolerance considerations, and the actual driving evidence must all be assessed together to determine whether the State’s case rests on reliable proof or forensic overreach. Bill Powers and the DWI and Drug Impaired Driving Lawyers at Powers Law Firm devote a significant portion of their criminal defense practice to complex impairment cases. Call or TEXT 704-342-4357 to schedule a confidential consultation.