By SUSAN ADELMAN, MD
As most might guess, marijuana is the commonest illegal drug in the United States. An estimated 48.2 million people used it at least once in 2019. The percentage of U.S. drivers with marijuana detected in their blood was 8.6% in 2007 and rose to 12.6% in 2013-14. Should marijuana be legalized nationally? For safety’s sake, are there legal blood limits for drivers?

Marijuana and hemp come from the Cannabis sativa plant.  Legally, hemp is defined as any part of the cannabis sativa plant that contains 0.3 percent or less of THC (tetrahydrocannabinol), while marijuana contains more than 0.3 percent THC. THC is the substance that causes a high. CBD (cannabidiol) does not. In some sources, cannabis is a Schedule 1 drug, as is heroin, but the Michigan Public Health Code says “Marihuana, including pharmaceutical-grade cannabis, is a schedule 2 controlled substance if it is manufactured, obtained, stored, dispensed, possessed, grown, or disposed of in compliance with this act and as authorized by federal authority.”

In 2018, the U.S. Congress passed the Agriculture Improvement Act, removing hemp from the federal Controlled Substances Act and effectively legalizing CBD if it comes from hemp. Confusingly, marijuana still may be illegal at the federal level, but 24 states have legalized it. Yet in October 2022, President Biden issued an executive order that pardons non-violent offenders. Now the Department of Health and Human Services has asked the DEA to consider moving marijuana to Schedule III, meaning that some restrictions would be lifted, but marijuana would still be a controlled substance. Supporters of this potential move are pleased, because it would have implications for the taxation of sellers, interstate commerce and research, but those in favor of making full legalization are disappointed. Also, it still would not fully free up banking services for sellers. Still, it would be a step.

In Michigan, anyone 21 and older can purchase recreational or medical marijuana, with no age limit since the Michigan Regulation and Taxation of Marijuana Act of 2018. The limit for possession of marijuana in Michigan is 2.5 ounces, for any use.

CBD, as purchased from licensed dispensaries, does have medical uses – Epidiolex, for certain types of seizures, also Dronabinol and Nabilone, both derived from CBD. These are used for nausea due to chemotherapy, and to boost the appetite of AIDS patients with wasting syndrome. Other indications include Alzheimer’s, ALS (Lou Gehrig’s Disease), Crohn’s disease, glaucoma, hepatitis C, severe and chronic pain, severe and persistent muscle spasms, and multiple sclerosis.

In contrast, marijuana sold on the street has been found laced with pesticides, heavy metals, glass, E.coli, the fungus aspergillus, PCP, methamphetamine, LSD, ketamine, cocaine, heroin, embalming fluid, even laundry detergent.

The majority of 52.5 million reported users in 2021 were between 18 and 25. Another 10.5% were 12 to 17, even though the adolescent brain is more sensitive to marijuana than the adult brain, and heavy use has been shown to impair brain development and functioning. Unfortunately, use during adolescence can lead to a loss of IQ that isn’t recoverable. It also may lead to temporary psychosis, even schizophrenia, especially among users who start very young and use it frequently. The Human Performance Drug Fact Sheets  of the National Highway Safety Organization (NHTSA) describe marijuana as addicting, and animal studies demonstrate that it causes physical dependence.

Recent research at Northwestern University links “recent and long-term marijuana use” to “changes in the human epigenome.” This means it changes how certain human genes are turned on or off. The researcher also “consistently identified one marker that has previously been associated with tobacco use, suggesting a potential shared epigenetic regulation between tobacco and marijuana use.”

According to the NHTSA,” Marijuana has been shown to impair performance on driving simulator tasks and on open and closed driving courses for up to approximately 3 hours.” But they say research is needed on the association between marijuana use and car crashes. Perhaps, but we know that marijuana affects balance, coordination, reaction time, the ability to make decisions, judgment, emotions, and other perceptions.

The US Office of Indigent Services (IDS) writes in 2021 “A number of States have set a THC limit in their laws indicating that if a suspect’s THC concentration is [above a certain level] (typically 5 ng/ml of blood), then the suspect is to be considered impaired,” but, according to an NHTSA 2017 Report to Congress, blood concentrations of THC correlate poorly with impairment. The problem is that marijuana does not act like alcohol. THC is stored in fatty tissues in the body, and it can be released back into the blood as long as 30 days later.

The key take-away is that “There is no evidence…that any objective threshold exists that establish [an] impairment base on THC concentrations in suspects placed under arrest for impaired driving.’

In short, when a driver is pulled over, it is hard for officers to assess blood levels of marijuana, and the usual tests of balance do not work, except perhaps the finger to nose test. So, asking again, should we even try to set legal limits? And, knowing what we do of its effects, should marijuana be legalized nationally? Or is it essentially legal already?