Bench + Bar of Minnesota

The cannabis-custody conundrum

How the adult-use cannabis law will affect custody matters

By Christopher Vatsaas and Melanie Nelson

Marijuana use is not a foreign issue to family courts. In Minnesota, however, the legalization of recreational marijuana in 2023 added a new layer to this legal onion. As of August 1, 2023, adults in Minnesota over the age of 21 can possess, use, and grow restricted amounts of marijuana.1 

The framework guiding custody and parenting time decisions in Minnesota is found in Minn. Stat. 518.17, subd. 1, otherwise known as “the best interest factors.” The main factor pertinent to marijuana use is number 5: “any physical, mental, or chemical health issue of a parent that affects the child’s safety or developmental needs.”2 The extent to which marijuana use affects a parent’s ability to parent and to ensure their child’s safety is paramount to the analysis. As with alcohol, other factors may also become relevant depending on the extent of a parent’s use of marijuana, such as factor 6 (“the history and nature of each parent’s participation in providing care for the child”) and factor 7 (“the willingness and ability of each parent to provide ongoing care for the child; to meet the child’s ongoing developmental, emotional, spiritual, and cultural needs; and to maintain consistency and follow through with parenting time.”)3 (Emphasis added).

In addition to considering how legalization should affect new family law cases, it is important to weigh how existing provisions in family law orders are affected. Family law orders routinely incorporate terms completely restricting the use of marijuana, or perhaps more generally “controlled substances,” with testing terms that trigger further conditions. The result of testing positive for marijuana use can be very serious. Parents may see their parenting time suspended, supervised, or heavily restricted until conditions are met.

Implicit biases

Implicit biases of parties, attorneys, judges, mediators, and evaluators have always played a role in the drug and alcohol provisions contained in parenting plans. Naturally, everyone is going to treat the legalization of marijuana differently based upon their subconsciously embedded personal viewpoints. These key players in any family law case may have differing views of alcohol use and how to create provisions in parenting plans that safeguard children while also monitoring use in a way that isn’t excessive. 

But in contrast to marijuana, alcohol involves familiar testing protocols, and those protocols offer a degree of clarity and immediacy that serve to manage implicit biases through data. 

Data collection

This implicates an important question: What qualifies as impairment and how do we measure it? There is currently no clear scientific method to determine impairment with marijuana use. While various types of tests can measure THC levels, THC levels are not reliable indicators of marijuana intoxication.4 THC metabolites linger for weeks after the last time someone uses, and they will still generate positive results using the standard testing methods.

One study in particular, conducted by RTI International, tested cognitive and psychomotor impairment with THC use and ultimately found that the toxicology tests (blood, urine, and oral fluid) showed that levels of cannabis component did not correlate with level of impairment.5 

One new testing method, brain imaging, has shown through a study to be 76 percent accurate in detecting impairment.6 Researchers used brain scans to look at the prefrontal cortex. The brains of individuals who have THC in their system look different from those who don’t. While brain imaging proved accurate in this study, it is not practical on a large scale, as that would require extraordinary investments in equipment and human resources. Immediacy, cost, and scalability are all important factors for a testing device that could be used in a family law context. But there is as yet no breathalyzer for cannabis intoxication.

Law enforcement is facing the same issue. Currently, law enforcement relies on field sobriety tests to determine whether a driver is impaired due to cannabis use. Some police departments are part of pilot programs to try potential new devices. One such device, OcuPro, gives the test-taker visual stimuli and measures the test-takers pupils’ size and movement in response.7 The test takes about one minute and provides immediate results on the device. This device was created by Minnesotans and is being tested by agencies across the United States. Last fall, Minnesota law enforcement agencies conducted a pilot program involving saliva testing.8 It will be important to follow the results of these pilot programs to see if any of these testing methods have potential viability in a family law context.

What we can learn from other states

In analyzing how Minnesota should handle the legalization of marijuana, it is helpful to look at how states that have had marijuana legalized for longer handle it. Unfortunately, there is limited appellate case law on the issue and thus few identifiable trends. This doesn’t necessarily come as a surprise, since district court judicial officers are given broad discretion; in family law, the justification for those decisions is that they must be in the best interests of the children. 

One of the cases regularly referenced is In re: the Marriage of Catherine Parr and David Lyman.9 This is a case out of the Colorado Court of Appeals, a state that was one of the first to legalize marijuana. Father was approved for a medical marijuana license due to back and knee pain from a motorcycle accident. One week prior, the parties signed a parenting agreement that required father to complete ongoing urinalysis tests and drug screenings to demonstrate that he was not using marijuana. Once he was approved for a medical marijuana license, father filed a motion requesting that the court eliminate the drug testing requirement. He admitted that he didn’t disclose that he had petitioned for the medical marijuana license. 

The district court decided that the parenting plan requiring urinalysis tests would remain in place because father voluntarily and knowingly agreed to the conditions. After months passed, mother filed a motion requesting a restriction of father’s parenting time due to failure to provide clean urinalysis tests and his request to the children to keep his use a secret. Father appealed. The district court ordered that father’s parenting time be supervised until he shows the court that his medical marijuana use is not detrimental to the child, and he cannot use medical marijuana while he is with the child. It further ordered that unsupervised parenting time is conditioned on father submitting a clean hair follicle test to the court and having weekly clean urinalysis tests. Father appealed. The court of appeals found that father’s medical marijuana use did not constitute endangerment and thus did not support a restriction of his parenting time. Mother did not demonstrate that father’s use created a threat to the physical and emotional health and safety of their child. But the court of appeals specifically noted that it was not making a finding that medical marijuana use may or may not constitute endangerment, but rather that it wasn’t shown in this case. 

Parr demonstrates a correlation to how Minnesota already navigates parental alcohol use. The legality of a substance does not affect the potential presence of an issue from a parenting perspective. The difference with marijuana use now that it is legalized is that it is no longer a question of whether the behavior poses a danger to the children and is illegal. Instead, we only need to focus on whether the use poses a danger to the children or otherwise tangibly affects their best interests.

In one case, the California Court of Appeals similarly found that medical marijuana use alone is not sufficient to show that the children are at risk of harm.10 There, the court of appeals maintained the district court’s restriction that father could not use marijuana in the home due to the negative effects of secondhand smoke on the children as well as father’s negative behavior changes toward the children and other people when he uses. Specifically, father is more irritable, has less patience, snaps at the children, uses corporal punishment, and is more violent toward his girlfriends. The court also highlighted father’s history of domestic violence, father’s use of marijuana prior to the doctor’s recommendation and his medical marijuana license, and side effects of marijuana smoke.

There are likely many parties to family law cases that now wish to change agreements or orders requiring testing given the change in the law. While the father in Parr ended up with a decision in his favor after defying his parenting agreement, it obviously required extensive litigation and presumably the costs attached to it. His parenting time had already been restricted for many months by the time the court of appeals agreed with him. Additionally, parents should not expect that the court will set no restrictions or oversight on their use. 

Texas, New York, and New Mexico have passed laws prohibiting child welfare agencies from using marijuana use as the sole factor in determining a parent or guardian is unfit.11 In California, the Department of Social Services modified its regulations to clarify that use or possession of marijuana is to be treated the same way as use or possession of alcohol or prescribed medications during investigations. Last fall, the Minnesota Department of Human Services revised its Child Maltreatment Intake, Screening, and Response Path Guidelines to reflect the legalization of marijuana in Minnesota. One child safety consultant specifically noted that the Minnesota Department of Human Services is trying to view marijuana and alcohol in a similar way. While child welfare agencies are not always involved in family law cases, their positions can have a major impact on the way a judge perceives chemical health concerns of parties to family law cases.

Looking ahead

Unlike alcohol, marijuana does have meaningful supporting research in relation to its medicinal value. Many states, including Minnesota, recognized as much in legalizing medical marijuana before recreational marijuana. Low doses of THC can help reduce anxiety.12 In a study completed on medical marijuana patients in Colorado, six out of eleven reported that marijuana use helped them be more calm and patient parents.13 Conversely, in another study, parents who use marijuana self-reported using more discipline (including physical and non-physical) than parents who do not use.14 With increased legalization, it will be important to continue to research and monitor the direct effect of marijuana use on parenting, especially with parents who use marijuana less frequently. Finally, another consideration is how a parent’s use may affect a child’s decision to use in the future. One study found that when mothers used cannabis, 81 percent of adolescents whose mothers used cannabis also used and 78.4 percent of adolescents whose fathers used cannabis also used.15 Needless to say, the conversation surrounding the intersection of family law and cannabis does not end with its legalization—but rather expands. 

CHRISTOPHER VATSAAS is a partner in the family law practice group at Chestnut Cambronne PA with a comprehensive family law practice, including serving as an ADR neutral.  He also is an adjunct professor at the University of St. Thomas School of Law, where he teaches advanced family law. 

MELANIE NELSON is an associate attorney in the family law practice group at Chestnut Cambronne PA, where her practice focuses exclusively on family law.  She also serves as the secretary of the Family Law League, a local family law organization focused on networking and collaboration among family law professionals. 



1 Minn. Stat. §342.09

2 Minn Stat §518.17, subd. 5

3 Id.


5 Id.



8 .

9 In re Marriage of Catherine Parr and David Lyman, 240 P.3d 509, 511 (Colo. App. 2010)

10 In re Alexis E., 90 Cal.Rptr.3d 44, 56 (Cal.Ct.App.2009)




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