The “Per Se” DWI Myth: Why North Carolina Law Does Not Support Conviction by Number Alone

Search the phrase “per se DWI North Carolina,” and the results look deceptively confident. AI summaries and legal directories will tell you that if your blood test hits a certain number, a conviction is inevitable.

That framing is not the law of North Carolina.

It is not the language of the statute. It is not the language used to instruct juries. It is a slogan that has been repeated so often it now masquerades as doctrine.

North Carolina’s DWI statute does not use the phrase per se impairment for alcohol or marijuana, and North Carolina’s jury instructions do not tell juries that a specific number automatically equals guilt.  That phrase does not appear anywhere in N.C.G.S. 20-138.1.

What the law recognizes is a single offense, Impaired Driving, proven under three specific evidentiary theories. None of those theories creates an automatic presumption of guilt based solely on a laboratory number.

If you have questions about the science behind your test results or would like to verify what the law actually requires in your situation, we invite you to contact the DWI defense lawyers at the Powers Law Firm to schedule a confidential legal consultation. Our firm helps clients in the Charlotte-Metro region including, Mecklenburg, Union, Iredell, Gaston, Lincoln and Rowan Counties with DUI/DWI charges.  For select matters involving Felony Death by Vehicle, Misdemeanor Death by Vehicle, and Felony Serious Injury by Vehicle, the firm is available for statewide consultation.

The Three Prongs of N.C.G.S. 20-138.1

To understand why the “Per Se” narrative is at best misleading, you must look at the statute itself. The State can prove Impaired Driving in one of three ways:

1. Appreciable Impairment: The defendant drove while under the influence of an impairing substance (Alcohol, Marijuana, Prescriptions, etc.).

2. 0.08 Alcohol Concentration: The defendant had an alcohol concentration of 0.08 or more at any relevant time after driving.

3. Schedule I Controlled Substances: The defendant drove with any amount of a Schedule I substance (or its metabolites) as listed in N.C.G.S. § 90‑89 (like Heroin or LSD) in their blood or urine.

Critical Note:

Marijuana is a Schedule VI controlled substance. It does NOT fall under the “Zero Tolerance” (“any amount”) prong of the statute.

To convict you of a Marijuana DWI, the State must prove actual, appreciable impairment. A number on a lab report is not enough.

Have more questions about the NC DWI laws?  Check out our free download of the North Carolina DWI Quick Reference Guide.

Scientific Reality vs. Legal Fiction: The Problem with Blood Numbers

In many “Drugged Driving” cases, the State introduces a blood toxicology report that looks damning. It is filled with high numbers and scientific names. But when you apply actual pharmacology to these numbers, the case for impairment often collapses.

Consider a hypothetical blood test result for Cannabis (THC). The State might wave a report showing a massive “32 ng/mL” reading to the jury. But what does that number actually mean?

Deconstructing the Drugged Driving Lab Report

Substance Name on Report	The “Number” (Example)	Scientific Reality	Legal Fiction
Tetrahydrocannabinol (THC)	3.5 ng/mL	This is the active psychoactive parent compound. 3.5 ng/mL may be observed in frequent users who are not appreciably impaired due to tolerance and residual redistribution from fat tissues.	The State implies “presence” proves you were high at the wheel. Fact: Science cannot pinpoint when you used based on this number alone.
11-nor-9-carboxy-THC (THCA/COOH)	32 ng/mL	This is the inactive metabolite. It has ZERO psychoactive effect. It stays in the body for days or weeks after use.	Inferring this “high number” (32) proves you were “loaded” or “high.” Fact: This number is historically interesting but does not establish current impairment.
11-hydroxy-THC	1.1 ng/mL	This is the active metabolite created by the liver.	Its low presence confirms the body processed the drug, but offers no definitive proof of the degree of impairment at the time of driving.

This is why “per se” limits for marijuana are unscientific. A daily user can be sober at 3.5 ng/mL, while a naive user might be appreciably impaired. The law does not allow a calculator to replace a jury’s judgment.

The Jury Instruction Trap: “Deemed Sufficient” is Not “Deemed Guilty”

The clearest demonstration that North Carolina rejects “per se impairment” is found in the North Carolina Pattern Jury Instructions (N.C.P.I. 270.20A)

When a jury hears a case involving a 0.08 BAC, they are not told using the PJI’s (the pattern jury instructions) they must convict. They are told:

“The results of a chemical analysis… are deemed sufficient evidence to prove a person’s alcohol concentration.”

“Sufficient” does not mean “conclusive.”

In State v. Narron, 193 N.C. App. 76 (2008), the North Carolina Court of Appeals clarified this distinction.

The Court held that this language creates a prima facie case, but it does not create a mandatory presumption of guilt.

The jury is still free to reject the test results based on reliability, machine error, or conflicting evidence.

The “Zero Tolerance” Unconstitutionality (Schedule I)

There is one exception in North Carolina law where the State attempts to impose a true “Per Se” rule, that being Schedule I Controlled Substances.

Under N.C.G.S. 20-138.1(a)(3), driving with “any amount” of a Schedule I substance (or its metabolites) is a crime. This includes drugs like Heroin, LSD, and Ecstasy.

This prong is constitutionally suspect.

Because the statute criminalizes the presence of metabolites, which can be inactive and non-impairing, that could potentially punish a person’s status (having used drugs in the past) rather than their conduct (driving while impaired).

Convicting a driver who is 100% sober simply because they have an inactive metabolite in their blood arguably violates Substantive Due Process.

There is no “rational basis” for the State to criminalize safe driving.

While North Carolina appellate courts have thus far ruled on the constitutionality of that aspect of the NC DWI statute, it remains a potential battleground for defense attorneys willing to challenge the apparent attempt to impose a “per se” standard.

FAQs | The Truth About Blood Tests, Drug Schedules, and “Per Se” Impairment

Is there a “legal limit” for marijuana in North Carolina?

North Carolina statutes contain no numeric “per se” standard for THC or marijuana metabolites. The State cannot secure a conviction based solely on a blood test result number. Prosecutors must instead prove appreciable impairment under N.C.G.S. 20-138.1(a)(1), demonstrating beyond a reasonable doubt that a driver’s mental or physical faculties were noticeably or “appreciably” affected at the time of driving.

Does an “Any Amount” rule apply to Cocaine or Methamphetamine?

N.C.G.S. 20-138.1(a)(3) restricts the “Any Amount” rule exclusively to Schedule I controlled substances (such as Heroin or LSD). Cocaine and Methamphetamine are Schedule II substances, meaning the State cannot rely on the mere presence of the drug or its metabolites to prove guilt. The prosecutor must present additional evidence of actual, appreciable physical or mental impairment.

Can I be convicted of DWI for taking my prescribed medication?

A valid prescription is not a defense against an Impaired Driving charge in North Carolina. N.C.G.S. 20-138.1 criminalizes driving while impaired by any substance. However, the State bears the burden of proving that the specific medication caused an appreciable impairment of your bodily or mental faculties. The central legal issue is not whether you took the medicine lawfully, but whether it caused you to lose normal control of your faculties at the time of driving.

What does “Deemed Sufficient Evidence” actually mean in a DWI trial?

“Deemed sufficient” defines the minimum evidence required to send a case to jury deliberation. It is not a mandatory instruction to convict. Under State v. Narron, this statutory language creates a permissive inference rather than a conclusive presumption. Jurors retain the ultimate authority to weigh the reliability of the chemical analysis against contradictory evidence of sobriety, such as clear speech, steady balance, or normal driving behavior captured on video (if such evidence exists).

Can I win a DWI case if my blood test is positive for drugs?

A positive toxicology report confirms the presence of a substance but does not scientifically prove impairment at the specific time of driving. Defense strategies often focus on the disconnect between the “number” in the lab report (which may reflect inactive metabolites) and the “reality” of the driver’s behavior on video. If the visual evidence shows normal mental and physical function, it can effectively rebut the State’s claim that the drug appreciably impaired the driver.

Is video evidence always available to challenge a DWI charge in North Carolina?

The NC DWI laws do not strictly mandate the recording of every traffic stop, though many North Carolina agencies now utilize body-worn and dashboard camera systems. This footage often serves as the most objective evidence in an impaired driving case, providing a direct check against the subjective notes of the arresting officer or the abstract numbers on a toxicology report. Defense attorneys review these recordings to demonstrate that a driver’s speech, balance, and ability to follow instructions contradict the State’s theory of chemical impairment.

How long do police save DUI videos?

Under policies like CMPD Directive 400-006, unflagged or misclassified body camera footage is subject to automatic deletion in as little as 90 days. If an officer inadvertently fails to tag your traffic stop as “Evidentiary,” the system may purge the file before your first court date. Furthermore, under N.C.G.S. § 132-1.4A, you cannot simply subpoena this video. Your defense lawyer must file a civil Petition for Release in Superior Court to secure it before the clock runs out.

The Bottom Line | Context Matters More Than Calculations

A criminal conviction should never rest on a spreadsheet of data that has not been subjected to strict statutory analysis. While the State may treat a blood test result as a conclusion, the law views it as merely one piece of evidence among many. We do not accept laboratory numbers or the all-too-often repeated misstatement of “per se impairment” as defaults for guilt. Rather, we examine whether those numbers legally equate to impairment under North Carolina standards.

Understanding forensic toxicology and criminal law requires careful attention to detail. If you are seeking clarity on the validity of your test results or the specific legal standards applicable to your case, the Powers Law Firm is prepared to review your matter. Our practice serves the Charlotte-Metro area, covering Mecklenburg, Union, Iredell, Gaston, Lincoln, and Rowan Counties for DUI/DWI defense. We also provide statewide representation for serious felony matters, including Felony Death by Vehicle, Misdemeanor Death by Vehicle, and Felony Serious Injury by Vehicle.