As marijuana becomes legal for recreational use in three of Indiana’s neighboring states, Indiana legislators are sharpening their focus on laws regarding driving while high on marijuana — and how to better detect drug-impaired drivers on the road.
House Bill 1119, authored by Rep. Wendy McNamara, R-Evansville, would allow oral fluid THC test results to be used in court as evidence in operating while intoxicated (OWI) cases. The proposal responds to growing concerns over how Indiana enforces laws against driving under the influence of marijuana — especially without a clear impairment threshold.
“THC is probably one of the trickiest things I’ve ever tried to nail down,” McNamara said during a Sept. 10, 2024, interim committee hearing, according to the Indiana Capital Chronicle. “This bill gives the state an opportunity to identify drivers who are truly impaired — using a qualified test already being used in the field.”
Indiana’s Approach to Driving High on Marijuana
Currently, Indiana driving laws on marijuana prohibit operating a vehicle with any detectable THC in the system, under a strict “per se” standard. This means drivers can face charges even if they’re not visibly impaired — a policy that critics argue lacks nuance and scientific backing.
By contrast, alcohol impairment has a decades-old, scientifically supported 0.08% blood alcohol concentration (BAC) threshold. But no universally accepted THC limit exists to determine marijuana impairment behind the wheel.
[RELATED: Indiana considers ban on marijuana advertising]
McNamara’s original bill proposed a five-nanogram THC limit in saliva. A recent amendment instead allows results from two specific roadside drug testing systems — the Drager DrugTest 5000 and SoToxa Oral Fluid Mobile Test System — to be admitted as evidence in court proceedings.
Lawmakers Debate Next Steps in Marijuana Driving Enforcement
Rep. Joanna King, R-Middlebury, was the only member of the House Courts and Criminal Code Committee to vote against the measure. “I’m concerned about false positives,” she said, as reported by the Indiana Capital Chronicle. “I just think this needs a longer, deeper look.”
Supporters, including prosecutors and traffic safety advocates, say Indiana marijuana driving laws must evolve to address increasing risks posed by impaired drivers.
“Drug driving is an increasing problem,” said Chris Daniels, traffic safety resource prosecutor with the Indiana Prosecuting Attorneys Council. “It’s costing more and more lives across the country and in the state.”
Daniels emphasized that under the bill, police cannot arrest someone based solely on oral test results. The test is only one factor — alongside other evidence like blood tests, field sobriety failures, or erratic driving — used to prove impairment under Indiana law related to driving high on marijuana.
Health effects of marijuana use
According to public health research, short-term marijuana use can:
- Impair short-term memory, making it difficult to learn and retain information.
- Disrupt motor coordination, interfering with driving skills and increasing crash risk.
- Alter judgment, potentially leading to risky behaviors — including those that increase the spread of sexually transmitted diseases.
- In high doses, cause paranoia and psychosis.
Beyond impaired driving, long-term or heavy marijuana use has been linked to:
- Addiction (affecting roughly 9% of all users, and up to 50% of daily users).
- Altered brain development, especially in adolescents.
- Poor academic outcomes and higher dropout rates.
- Lasting cognitive impairment and reduced IQ in frequent teenage users.
- Diminished life satisfaction and lower long-term achievement.
- Chronic bronchitis symptoms.
- Increased risk of psychosis, especially in those with a predisposition to mental illness.
These outcomes have shaped Indiana’s more conservative stance on legalization — reinforcing the argument that Hoosier laws on driving high and marijuana use should prioritize caution, public health, and safety.
Crossing State Lines Raises Complications
Though Indiana has not legalized marijuana for recreational or medical use, Illinois, Michigan and Ohio have — and Kentucky now permits limited medical use. That means Hoosiers frequently cross state lines, purchase marijuana legally, then return to Indiana roads, where driving high remains illegal.
Michael Moore, testifying on behalf of the Indiana Public Defender Council, warned against relying too heavily on saliva test results alone.
“These test results will come in without any real evidence to refute it,” Moore said. “Even though they can’t make an arrest solely based on them, someone can still be charged and face the consequences” (Indiana Capital Chronicle).
Moore said that if Indiana insists on maintaining its per se law, it should at least include a threshold like five nanograms to better reflect actual impairment.
Remote Testimony and Public Safety
The bill would also allow state lab technicians to testify remotely in court, helping reduce strain on the Indiana State Department of Toxicology. Daniels noted that in 2025 alone, technicians have already spent 75 hours traveling but just five hours on actual court testimony.
McNamara defended the decision to name specific test brands in the legislation, citing reliability and consistency across jurisdictions. “Consistency is the key right now, since it’s so new,” she said.
Will Indiana update its laws on driving high?
As more states legalize marijuana, Indiana is grappling with how best to protect public safety and ensure the integrity of its legal system. Lawmakers are not debating legalization — but rather how to fairly and effectively enforce Indiana laws on driving high on marijuana as THC use becomes more prevalent.
The outcome of House Bill 1119 could shape the future of drug-impaired driving enforcement in Indiana, setting clearer standards for how law enforcement and courts handle cases involving marijuana behind the wheel.
The bill did not receive a hearing in the Indiana Senate.
This article was based on the reporting of the Indiana Capital Chronicle.