New Jersey Marijuana DUI: Legal to Use, Illegal to Drive Impaired

The legalization of marijuana in New Jersey has led many residents to believe that cannabis use is without serious legal risk. While it is true that adults can now legally purchase and consume marijuana, the rules change the moment you get behind the wheel. Driving under the influence of cannabis is treated just as seriously as driving drunk, and the penalties can be just as severe. 

If you are facing a marijuana DUI charge, working with an experienced New Jersey DUI lawyer can make all the difference. Our skilled attorneys at The Kugel Law Firm understand where to find weaknesses in the state’s case, from questionable field sobriety tests to unreliable toxicology results. For experienced guidance and aggressive representation, contact us today at (973) 854-0098 to schedule a consultation and take the first step toward protecting your future.

N.J.S.A. 39:4-50 and the Stance on Impairment

New Jersey law takes an uncompromising stance on driving while impaired. Under N.J.S.A. 39:4-50, it is illegal to operate a motor vehicle while under the influence of alcohol, marijuana, or any other intoxicating substance. Marijuana impairment is treated with the same seriousness as alcohol-related offenses. This legal framework sets the stage for how marijuana DUIs are prosecuted, highlighting the significant risks drivers face even as cannabis has become more widely accepted in society.

How New Jersey’s DWI Statute Treats Marijuana Like a High-Tier Alcohol Offense

The foundation of every driving while intoxicated (DWI) charge in New Jersey is N.J.S.A. 39:4-50. This statute makes it unlawful for a person to operate a motor vehicle “while under the influence of intoxicating liquor, narcotic, hallucinogenic or habit-producing drug.” Importantly, the law makes no distinction between impairment caused by alcohol, marijuana, or any other controlled substance.

The penalties for a marijuana-related DUI are arguably more serious than those for a high-tier alcohol offense, defined as having a blood alcohol concentration (BAC) of 0.10 percent or higher. This means that even first-time marijuana DUI offenders face heightened consequences from the outset. Although cannabis legalization may have fostered a perception of leniency, the legal reality is far different. New Jersey treats marijuana impairment behind the wheel with the same seriousness as alcohol intoxication.

Medical Marijuana Is Not a Defense for Impaired Driving

One of the most common misconceptions arises among individuals who are registered under New Jersey’s Compassionate Use of Medical Marijuana Act. While medical cannabis is legal for qualified patients, it does not provide an exemption from DUI laws.

Just as someone prescribed a powerful painkiller or sedative cannot legally drive while impaired, a medical marijuana patient is subject to the same restriction. The state’s position is clear: having a valid prescription or marijuana card does not serve as a legal defense if impairment is proven. Driving under the influence remains a violation, regardless of the source of the substance.

What “Impairment” Means in Court

Unlike alcohol DUIs, where a BAC of 0.08 percent or higher creates a per se violation, New Jersey has no defined THC limit that automatically proves intoxication. Because of this, marijuana DUI cases require prosecutors to build their case around observable impairment.

To convict, the state must prove beyond a reasonable doubt that marijuana use caused a substantial deterioration or diminution of the mental faculties or physical capabilities of the driver. In other words, prosecutors must show that the individual could not operate their vehicle with the same caution and control as a sober driver.

This reliance on subjective evidence, such as field sobriety tests, officer observations, and expert testimony, creates room for challenges by the defense. The absence of an objective THC standard means each case hinges on how well the state can demonstrate actual impairment, making this the central battleground in marijuana DUI trials.

New Jersey DUI Attorney Rachel Kugel

The Three Pillars of a Marijuana DUI Prosecution

The state’s case begins with a patrol officer’s subjective observations, progresses to a specialized evaluation, and culminates in a scientific test that, paradoxically, cannot directly prove impairment.

Pillar 1: Officer Observations and Field Sobriety Tests (FSTs)

The process starts with the initial traffic stop. An officer must have a legally valid reason, known as “reasonable suspicion,” to pull a vehicle over. This may include observing erratic driving, drifting between lanes, or other suspicious behavior.

Once the stop is made, the officer looks for physical signs commonly associated with marijuana use, such as bloodshot eyes, or slow or slurred speech. Importantly, under New Jersey’s revised laws, the smell of marijuana alone is no longer enough to establish probable cause for a vehicle search.

If the officer suspects impairment, the driver may be asked to perform a series of Standardized Field Sobriety Tests (SFSTs). These tests, endorsed by the National Highway Traffic Safety Administration (NHTSA), were designed primarily for detecting alcohol impairment, not marijuana use. This fact becomes crucial for the defense. The three standardized tests are:

• Horizontal Gaze Nystagmus (HGN): The officer observes the driver’s eyes for involuntary jerking as they follow a stimulus like a pen or finger.
• Walk and Turn: The driver takes nine heel-to-toe steps along a straight line, turns, and repeats the sequence back.
• One Leg Stand: The driver must balance on one foot, raise the other six inches off the ground, and count aloud for 30 seconds.

The officer’s subjective interpretation of these results then forms the basis for the next stage of the investigation.

Pillar 2: The Drug Recognition Expert (DRE) Evaluation

If the arresting officer concludes that the driver shows signs of impairment not explained by alcohol, a Drug Recognition Expert (DRE) may be called in. A DRE is a specially trained officer certified to recognize impairment caused by seven categories of drugs, including cannabis.

The DRE follows a standardized 12-step protocol, designed to be systematic but vulnerable to bias. The process typically includes:

• Breath Alcohol Test to rule out alcohol as the cause.
• Interview with the Arresting Officer, which risks introducing confirmation bias since the DRE is primed with the officer’s observations.
• Preliminary Examination, including medical questions and general observations.
• Eye Examinations, such as checks for nystagmus and convergence.
• Divided Attention Tests, repeating SFSTs, and adding others such as the Finger to Nose test.
• Vital Signs, measuring pulse, blood pressure, and body temperature.
• Dark Room Examinations, evaluating pupil size under different lighting.
• Muscle Tone Assessment for rigidity or flaccidity.
• Check for Injection Sites.
• Questioning the Subject about recent drug use.
• Forming an Opinion about impairment and the drug category.
• Requesting Toxicological Testing to support the evaluation.

While the DRE evaluation appears scientific, many elements are still rooted in subjective judgment, which provides opportunities for defense attorneys to challenge the conclusions.

Pillar 3: Chemical Testing – The Limits of Blood and Urine Evidence

The final pillar of the state’s case is chemical testing through blood or urine samples. These tests detect THC or its metabolites, but they face a fundamental limitation: they cannot determine actual impairment at the time of driving.

THC can remain in the body for days or even weeks after use, long after its psychoactive effects have worn off. A positive test merely proves past cannabis consumption, not whether the driver was impaired when stopped. This limitation creates a scientific gap in the prosecution’s narrative, undermining the weight of the evidence.

Ultimately, a marijuana DUI case in New Jersey is not built on a single objective measurement. It is constructed from layers of officer observations, specialized evaluations, and toxicological reports that cannot conclusively prove impairment. Each stage introduces subjective elements and potential weaknesses, giving defense counsel critical opportunities to challenge the state’s case.

Pillar / Stage	Key Methods / Components	Limitations / Challenges
Pillar 1: Officer Observations and Field Sobriety Tests (FSTs)	Officer observations such as bloodshot eyes and slow or slurred speech; performance on Horizontal Gaze Nystagmus, Walk and Turn, and One Leg Stand.	Field Sobriety Tests were designed for alcohol detection and may not accurately measure marijuana impairment; results rely on officer judgment.
Pillar 2: The Drug Recognition Expert (DRE) Evaluation	A 12-step evaluation including a breath alcohol test, interview with the arresting officer, preliminary examination, eye examinations, divided attention tests, vital signs, dark room examinations, muscle tone assessment, injection site check, questioning, forming an opinion, and requesting toxicology.	The process depends on subjective interpretation and can be influenced by confirmation bias; it is not a direct scientific measure of impairment.
Pillar 3: Chemical Testing – The Limits of Blood and Urine Evidence	Laboratory analysis of THC and metabolites in blood or urine samples.	THC presence does not confirm impairment at the time of driving; it can remain in the body long after psychoactive effects have worn off.

Why THC in Your System Does Not Equal Impairment

The attempt to prosecute marijuana DUI cases using a framework designed for alcohol is the single greatest weakness in the state’s strategy. This approach fails because it ignores the fundamental scientific differences in how the body processes THC compared to alcohol. This scientific mismatch provides a powerful foundation for mounting a strong legal defense.

THC vs. Alcohol Metabolism

The distinction between alcohol and THC begins at the molecular level. Alcohol is water-soluble, which means it distributes evenly throughout the body’s water content. This creates a predictable and consistent correlation between blood alcohol concentration (BAC) and impairment in the brain. Because of this, BAC testing is considered a reliable and standardized measure of intoxication.

THC, on the other hand, is lipophilic, or fat-soluble. When cannabis is consumed, THC is quickly absorbed into the bloodstream but then rapidly disperses into fatty tissues and organs, including the brain. From there, it is released slowly over time. This process means that blood THC levels peak shortly after consumption and decline quickly, even though the subjective feeling of impairment may peak later and last for hours.

As a result, a blood test taken even an hour or two after driving can show a relatively low THC concentration that has no clear correlation to the actual level of impairment at the time of driving. In short, THC presence in the blood is not a reliable reflection of real-time intoxication.

The Problem with Per Se Limits

Because THC is metabolized so differently from alcohol, creating a per se legal limit for marijuana is scientifically problematic. A per se limit is a fixed blood concentration that automatically defines impairment, such as 0.08 percent for alcohol.

Major research bodies, including the National Highway Traffic Safety Administration (NHTSA) and the American Automobile Association (AAA), have found no reliable link between a specific THC blood concentration and an increased risk of causing a crash. A report from the NHTSA to Congress even concluded that “someone can show little or no impairment at a THC level at which someone else may show a greater degree of impairment.”

In effect, the state is asking courts to make a leap of faith by treating THC levels as equivalent to alcohol levels, despite clear scientific evidence that the two cannot be compared in this way.

Unreliability of Field Sobriety Tests for Cannabis

The state’s reliance on Field Sobriety Tests (FSTs) further weakens its case. These tests were originally developed to measure alcohol impairment and validated for their ability to predict a BAC of 0.08 percent or higher. Their applicability to marijuana impairment is highly questionable.

A major study supported by the National Institute of Justice (NIJ) examined this issue and found that the Walk and Turn and One Leg Stand tests were “not sensitive to cannabis intoxication.” Researchers concluded that THC levels in biofluids were not reliable indicators of impairment, and that SFSTs “were not effective in detecting marijuana intoxication.”

Another randomized clinical trial found that while officers could sometimes distinguish between subjects who consumed THC and those given a placebo, the overlap was substantial. Nearly half of the placebo group was still classified as impaired based on their performance, revealing a high rate of false positives.

Handling a Marijuana DUI Stop in New Jersey

Understanding your constitutional rights during a traffic stop is critical. In a marijuana DUI investigation, the procedural requirements for law enforcement are significantly more stringent than in a typical alcohol-related case. These requirements create opportunities for mistakes, and such errors can lead to the suppression of key evidence.

The Implied Consent Law Does Not Apply to Drug Tests

One of the most important distinctions between an alcohol DUI and a marijuana DUI in New Jersey lies in the Implied Consent Law under N.J.S.A. 39:4-50.2. This statute provides that anyone driving on a public road has implicitly agreed to submit to a breath test if arrested for drunk driving. Refusing a breath test in an alcohol case leads to a separate and severe Refusal charge.

However, this law applies only to breath tests for alcohol. It does not extend to chemical testing for drugs. This means that you cannot be charged with Refusal for declining to provide a blood or urine sample in a marijuana DUI case. The absence of this leverage significantly changes the balance of power between police and drivers when cannabis is involved.

Your Right to Refuse Blood and Urine Samples Without a Warrant

Under the Fourth Amendment of the U.S. Constitution, every person has protection against unreasonable searches and seizures. A blood or urine test is considered a search, which means police cannot compel you to provide a sample without either your voluntary consent or a valid search warrant.

The Importance of a Valid Warrant or Voluntary Consent

When law enforcement seeks a blood or urine sample, they have only two options:

• Consent: An officer may ask you to submit voluntarily. For this consent to hold up in court, it must be given knowingly and without coercion. You must also be informed of your right to refuse. If you do consent, it becomes much more difficult for your attorney to later challenge the admissibility of the test results.
• Warrant: If you decline to provide consent, the officer must seek a search warrant from a judge. To secure one, the officer must present sufficient evidence of probable cause that you were impaired. This evidence usually includes observations of your driving behavior, physical appearance, and performance on field sobriety tests or a drug recognition evaluation.

If a warrant is issued and blood is drawn, the law requires that the procedure be done properly. The draw must be conducted in a medically acceptable manner by a qualified professional, such as a nurse or phlebotomist, in a sanitary setting like a hospital. It cannot be performed by an officer at the roadside or in a police station. Any failure to follow these procedures can be grounds for a defense attorney to file a motion to suppress the test results.

Protecting Your Rights After a Marijuana DUI Charge

Marijuana may be legal in New Jersey, but driving under its influence carries harsh penalties and lasting consequences. From traffic stops to field sobriety tests and chemical reports, the state’s case is often built on subjective evidence that can be challenged. Understanding your rights and how the law treats marijuana DUIs is the first step in protecting yourself.

If you are facing charges, you do not have to fight alone. An experienced New Jersey DUI lawyer can identify weaknesses in the prosecution’s case and build a strong defense on your behalf. For aggressive representation and knowledgeable guidance, contact The Kugel Law Firm at (973) 854-0098 today. Taking action early can make all the difference in protecting your record, your license, and your future.