Legislating Marijuana Impaired Driving: Proposed Changes to Ohio Law

Colorado became the first state to legalize marijuana for adult recreational use in 2012. Since then, 23 other states now allow their adult residents to legally consume cannabis. This major policy shift brought questions about the impact on public health as well as public safety, including efforts to detect impaired driving caused by marijuana use. States have struggled to define what constitutes marijuana impairment and how such impairment should be measured given the lack of clear biological thresholds like those found with alcohol use.

The Ohio General Assembly is currently considering Senate Bill 55, which would enact changes to how individuals are tested for impairment, the overall Delta-9 THC limits an individual may have in their body while operating a vehicle, and a new evidentiary standard for impairment. This page provides a comparison of the proposed statute and Ohio’s current law in respect to marijuana impairment, and how these practices compare to other states.

There are two main components that are used for detecting marijuana impairment:

• Delta-9-Tetrahydrocannabinol (THC – Active): Delta-9 THC is the primary psychoactive ingredient of marijuana. Delta-9 is an isomer of tetrahydrocannabinol and is considered the most psychoactive cannabinoid within cannabis. Delta-9 THC is often considered active THC. Active THC levels immediately spike upon consumption and decline rapidly afterwards. Some states use it to determine impairment levels via a blood sample analysis.

• 11-Nor-9-carboxy-Δ9-tetrahydrocannabinol (THC Metabolite – Inactive): Often referred to as THC-COOH, this metabolite of THC is formed in the body after cannabis is consumed and metabolized. THC-COOH is inactive and not considered intoxicating. Unlike THC, THC-COOH levels in urine can remain detectable for days and sometimes weeks after usage.

Unlike alcohol impairment, marijuana impairment is difficult to measure due to several factors:

1. Absorption and Metabolism

Unlike alcohol, which is metabolized at a steady rate allowing a clear link to impairment, THC accumulates in fat cells and is released slowly at different rates based on individual physiology. After consuming marijuana through combustion, users begin to notice effects almost immediately and their active THC (delta-9) levels spike within 2-5 minutes. Active THC levels then drop rapidly to about half of the initial amount within 15 minutes. Reports indicate active THC levels will be in single digits within one hour and remain there for up to eight hours depending on the user and amount consumed. Consumption through edibles results in a delayed peak time of active THC level concentration, usually within 1-3 hours and slower drop off.

Marijuana’s non-psychoactive metabolite, THC-COOH or 11-Nor-9-Carboxy-THC, begins to appear within a half hour after usage. Marijuana metabolites can be detected for an extended period (days or even weeks) after usage and varies for each user. Marijuana metabolites are often used to determine if an individual has consumed but are rarely used to determine the level of impairment.

2. Effect Duration and Variability

Unlike alcohol impairment effects, which follows a predictable curve for the vast majority of individuals, marijuana effects depend on many factors including an individual’s tolerance, method of consumption, or type of product consumed. People with the same levels of active THC or THC metabolite in their systems can experience vastly different levels of impairment. For alcohol, impairment has been established to occur at a blood alcohol concentration (BAC) at or above 0.08%. To date, there is no equivalent scientific consensus on what levels of THC are associated with impairment across the whole population.

3. Lack of a Reliable Field Test

Breathalyzers have been scientifically validated to accurately measure alcohol levels, providing law enforcement with a quick and reliable way to assess intoxication in the field. There is no equivalent test for marijuana. While blood, urine, and saliva tests can detect THC and its metabolites, they cannot determine whether the person was impaired at the time the test was administered, and they are generally difficult to undertake in the field (there have been some developments on this front for saliva testing). Thus, the only way a police officer can assess whether someone is impaired in the field is through the standard field sobriety tests.

The vast majority of states’ statutes do not mention marijuana specifically but rather include marijuana under the definition of a drug, controlled substance, or intoxicant. Nevertheless, 16 states explicitly address marijuana, cannabis, or delta-9-tetrahydrocannabinol in their laws.

There are three general ways statutes delineate what constitutes impairment:

• General impairment – All 50 states’ statutes include a generic prohibition for individuals to operate a motor vehicle if a substance impairs their ability to safely operate the vehicle. An individual can be considered impaired if under the influence of a drug, controlled substance, alcohol, or a combination of these substances. These parts of statutes generally remain silent on the specifics of how law enforcement agents determine whether someone is impaired.
• Zero Tolerance – Ten states’ statutes contain an additional section that specifically prohibits motor vehicle users from being under the influence of any detectable amount of a controlled substance or drug, including marijuana. In other words, if a law enforcement agent observes general impairment, a follow-up blood, urine, or saliva test that shows any detectable amount of THC or THC metabolites would constitute further proof of drivers’ impairment.
• Per Se – In addition to the ten states with zero tolerance laws, seven states’ statutes (see Table 2) set limits on how much of a substance an individual may have in their body while operating a vehicle. Specific to Tetrahydrocannabinol (THC), states measure active or inactive THC (THC metabolite) in nanograms per milliliter (ng/ml), which can be detected in blood, urine, saliva, and other bodily fluids.

Table 1. Number of States by Marijuana Impairment Category

Table 2. Per Se Limits by State

Figure 1. Marijuana OVI Laws by State

In January 2025, the Ohio General Assembly introduced Senate Bill 55 titled, Regards operating under the influence of marihuana, OVI evidence. The bill proposes the following legislative changes:

Marijuana and OVI Provisions

• Increases the per se limit for marijuana in whole blood from 2 ng/mL to 5 ng/mL delta-9 THC for automatic OVI violations.
• Eliminates marijuana metabolite testing from being used as a basis for per se OVI violations.
• Removes urine, blood serum, or plasma THC testing as a basis for automatic violations.
• Introduces a new evidentiary standard allowing courts to infer impairment if:
  • The person has at least 25 ng/mL of THC in urine.
  • The person has between 2 ng/mL and 5 ng/mL of THC in whole blood.

Admissibility of Evidence in OVI Cases

• Clarifies that any evidence regarding alcohol or drug concentration is subject to the Rules of Evidence, including expert testimony.
• Ensures that evidence of alcohol or drug levels does not exclude additional evidence related to:
  • The analysis of blood, urine, breath, or oral fluid.
  • The methods, processes, and reliability of the testing equipment.
• This bill loosens the THC limits for automatic OVI violations while shifting to an inference-based approach for lower THC concentrations. The new standard allows additional evidence and rebuttals in court rather than relying solely on strict per se limits.

Law enforcement uses a variety of tests to detect marijuana impairment, including:

• Blood
• Urine
• Oral Fluid Analysis
• Visual Indicators/Horizontal Gaze Nystagmus

The first line of detection generally involves the administration of one of the Standardized Field Sobriety Tests, including the walk and turn test, one leg stands, the horizontal gaze nystagmus (HGN) test, or the Field Impairment Test developed specifically for drug impairment. It is worth noting that the HGN test can often detect impairment from a variety of substances, but it is not sufficient at detecting marijuana impairment.

In an attempt to support standardized field tests, law enforcement often employs other tests, including saliva, blood, and urine analysis. For instance, Michigan's pilot program for oral fluid roadside testing for individuals suspected of impaired driving began in 2016 and the program was eventually expanded to all counties in 2019. Indiana has been utilizing this type of test since 2020. As of right now, the testing is still in its infancy and often faces scrutiny for how reliable it can be in certain contexts. Nevertheless, some Ohio law enforcement agencies have also started to test deployment of oral fluid testing, including the Ohio State Highway Patrol (OSHP). As of right now, approximately 25 OSHP officers across the state have access to oral fluid collection kits. At present, the test does not test for specific concentration of a substance or its metabolite. Therefore, the test cannot be used as evidence for a “per se” violation, but it can effectively determine the presence of a substance or its metabolite.

In addition to oral fluid testing, law enforcement may use urine or blood analysis for detecting levels of impairment. Urine analysis tests may be used to detect consumption but cannot effectively measure impairment as urine tests screen for the non-psychoactive metabolite, which can be detected for extended periods of time. For an exact measurement, law enforcement must collect a blood sample and run tests to determine the level of THC in a user’s body. Unlike urine analysis, blood tests can determine the level of active THC in a user’s system. However, blood testing is often difficult to perform and expensive for law enforcement. On top of this, THC rapidly leaves the body after consumption, adding some uncertainty to a blood test depending on the time of the incident and when the test is administered, as well as other factors like frequency of use and body composition of the user.

As of 2025, the FBI National Incident-Based Reporting System (NIBRS) allows law enforcement to track crime incidents, which includes incidents involving a suspected drugged driver. Ohio deploys their own voluntary reporting system in accordance with NIBRS standards and it is referred to as the Ohio Incident-Based Reporting System (OIBRS). Under this system, agencies are able to report the applicable crime and its statute, as well as what type of substance was involved in the incident. However, not every Ohio agency participates in the voluntary program and some local agencies maintain their own databases not in accordance with OIBRS. As a result, it is difficult to say with a great level of certainty how often OVI incidents in Ohio are marijuana related.