Dabbing & Driving
Without reliable science behind blood THC limits, Kentucky’s laws will punish patients while doing little to improve road safety.
As more states adopt medical and adult-use cannabis laws, lawmakers have rushed to introduce cannabis-impaired driving bills. In the rush, many legislatures have adopted laws with steep penalties but little to know corresponding scientific basis for assigning guilt. Eighteen states currently have zero-tolerance or non-zero per se laws on cannabis use. Zero-tolerance laws make it illegal to operate a motor vehicle with any measurable amount of a specific substance in the body. Per se laws make it illegal to drive with amounts of a specific substance that exceed set limits. Of those 18 states with cannabis driving laws, ten have zero tolerance for THC and metabolites, and four states have zero tolerance for THC but no restriction on metabolites. Five states have per se laws that cover one or more drugs. One state (Colorado) has a permissible inference law for THC, where exceeding a set blood concentration allows the court to infer impairment.
In Kentucky, it is unlawful to drive under the influence of any drug that impairs driving ability. Cannabis is included in that definition, and Kentucky’s law equally applies to non-medical and patients registered in the state medical cannabis program. People who are observed by law enforcement to be unsafely driving may be pulled over and administered a field sobriety test. Kentucky’s implied consent law states that any person operating a car automatically consents to chemical tests if an officer has reasonable grounds to believe a DUI has occurred. To prove the presence of cannabis, investigators must obtain a warrant and collect a blood sample. There is no breath analysis test like there is for alcohol. Kentucky defines the upper limit of THC as 5 nanograms per milliliter (ng/mL) of blood. For reference, 1 nanogram is one billionth of a gram.
The pharmacology of THC is complex. Its lipophilic nature, active metabolites, multiple routes of administration, and interplay of many compounds within cannabis make it impossible to draw a linear relationship between cannabis levels and impairment. Effects on motor skills and cognition vary widely in the general population. Some effects are dose-dependent, but they are influenced by the route of administration, GI motility, frequency of use, body fat composition, and duration of use. In states like Kentucky, the per se THC blood limit for determining driving impairment lacks a solid scientific basis.
If you are arrested in Kentucky for impaired driving, and your blood cannabinoid level is above 5 ng/mL (taken within 2 hours of operating a car), you could face up to 30 days in jail and fines up to $500. You may also have your driver’s license suspended for up to 4 months. Those penalties go up on subsequent offenses. In short, heavy cannabis users, first-time users, and medical cannabis patients alike may pay a significant price for any cannabis detected in the blood. Current blood tests cannot distinguish among these groups of users. Furthermore, the blood level test cannot definitively say if any of these people are impaired at any given time.
Kentucky’s current cannabis-impaired driving laws highlight the widening gap between policy and science. While many states have adopted a per se blood THC limit of 5 ng/mL, the evidence clearly shows that such thresholds are not reliable indicators of impairment. Unlike alcohol, THC does not correlate in a linear way with functional ability. THC blood levels are heavily influenced by factors such as frequency of use, metabolism, route of administration, and body composition. As a result, medical cannabis patients may face severe penalties even when they are not impaired, while occasional users could fall below the legal threshold yet still be unsafe to drive. By relying on outdated or scientifically unsupported measures, Kentucky risks punishing patients and responsible consumers without truly improving road safety. A more rational approach would prioritize observable impairment testing, supported by toxicology only as corroborating evidence, to create laws that protect public safety without criminalizing legitimate medical use.
References
Governors Highway Safety Association. Drug‑Impaired Driving. GHSA. Published January 2024. Accessed September 13, 2025. https://www.ghsa.org/state-laws-issues/drug-impaired-driving/.
Mastropietro KF, Rattigan JA, Umlauf A, et al. Short‑term residual effects of smoked cannabis on simulated driving performance. Psychopharmacology. 2025 Sep 6. doi:10.1007/s00213‑025‑06880‑1.