by Emma Wozniak, Associate Member, University of Cincinnati Law Review Vol. 93
I. Introduction
In 2024, Gallup’s Consumption Habits survey revealed that 15% of American adults reported that they smoke cannabis.[1] The number of cannabis smokers has increased steadily since 2013, when only 7% of adults reported cannabis use.[2] The rise in cannabis use is likely due to an increasing number of states legalizing cannabis. While cannabis is still federally prohibited in the United States, as of January 2025, twenty-four states have legalized recreational cannabis use and thirty-nine states have legalized medical use of the drug.[3] Legislation in these states typically allows individuals aged twenty-one and over to not only grow or possess cannabis but also to purchase it from licensed dispensaries.[4] A growing industry has emerged to fulfill the demand for legalized cannabis, ranging from the cultivation of the plant to retail services for consumers.[5]
Since cannabis is not federally regulated, states have the discretion to regulate and monitor the drug.[6] The patchwork of state-by-state regulations can create significant issues for recreational and medicinal cannabis consumers.[7] While it is generally safer to purchase cannabis products from a dispensary, researchers have found contaminants like heavy metals, microbes, pesticides, and mold in the legal cannabis supply.[8] The presence of these contaminants poses a significant health hazard for recreational and medicinal users.[9] This article examines how inconsistent state regulations contribute to cannabis contamination, creating potential health risks for consumers. Part II of this article will provide background on the history of cannabis legislation in the United States and the harmful substances that have been found in cannabis. Part III will discuss the various state regulations regarding the contamination of cannabis and the similarities and differences among them. Finally, Part IV will conclude by offering suggestions for regulation and monitoring to address the contamination issue.
II. Background
Throughout the 19th and early 20th centuries, cannabis was widely used in the United States as a medicine without federal restriction.[10] However, as the recreational use of cannabis began to gain popularity in the early 1900s, so too did the movement to regulate the drug.[11] Advocates of regulation associated the recreational use of cannabis with the influx of Mexican immigrants into the United States.[12] Anti-immigrant sentiment, particularly against Mexican immigrants, fueled public fear of cannabis, linking its use to crime and social disorder.[13] In 1915, California made it illegal to possess cannabis; the first among a wave of states that rolled out similar prohibitions.[14] In the early 1930s, twenty-nine states criminalized cannabis use and in 1937, the federal government followed suit by passing the Marijuana Tax Act.[15] The federal government continued to tighten the reins on cannabis use by including cannabis in the Federal Narcotics Control Act of 1956.[16] In 1970, Congress classified cannabis as a Schedule I substance, finding that there was no acceptable medical use for cannabis and that it was among the class of drugs with the highest potential for misuse.[17]
Public sentiment toward cannabis shifted again in the late 1900s. In 1996, California changed its stance and became the first state to legalize the medical use of the drug.[18] California’s Proposition 215 created the ongoing tension between federal and state laws criminalizing cannabis that continues to this day.[19] Over fifteen years later, on January 1, 2014, Colorado became the first state to legalize sales of recreational cannabis.[20] Now, in 2025, medical cannabis is legal in thirty-eight states and recreational use is legal in twenty-four states.[21] On May 21, 2024, the U.S. Department of Justice Drug Enforcement Administration proposed the transfer of cannabis to Schedule III under the Controlled Substances Act, likely because of the number of states that have legalized cannabis.[22] Schedule III drugs are defined as drugs with a moderate-to-low potential for dependence and currently have an accepted medical use.[23] While rescheduling the drug would not automatically make cannabis legal, it would open the door to medical marijuana use and allow for government agencies to conduct research on the safety and health implications of cannabis.[24] However, until rescheduling is finalized, regulation and research remain under state control.[25]
As states legalize cannabis not only has law enforcement, tax collectors, and entrepreneurs watched the legislation closely, but environmental health experts have also kept an eye on regulations.[26] Research has shown that cannabis products can impart incredibly harmful contaminants to users including molds, bacteria, pesticides, heavy metals, and solvents.[27] Creating policies to limit user exposure to these contaminants is not straightforward.[28] Cannabis products come in an array of forms that can be smoked, vaporized, or ingested orally.[29] The dosage and administration of the drug can impact the way contaminants interact with a user’s body.[30] For example, the inhalation of contaminants like pesticides or herbicides could have a more toxic effect on users since heating these chemicals can alter their composition.[31] The Food and Drug Administration (FDA) and the Environmental Protection Agency (EPA) have not provided any guidance on regulating contaminants to the states, leaving states to determine on their own how to protect cannabis users.[32]
The four common contaminants identified in cannabis products are microbes, plant growth regulators, heavy metals, and solvents.[33] The first category of contaminants, microbial contamination includes bacteria, insects, and mold.[34] Greenhouse and outdoor cultivation of cannabis is less likely than indoor operations to become contaminated by bacteria like Escherichia coli (E. coli), Salmonella, and Clostridium, or molds that can produce carcinogenic mycotoxins like aflatoxin B1 which suppresses growth and immune system functioning.[35] Aflatoxin findings are especially concerning for users since evidence suggests aflatoxins can survive the pasteurization and smoking processes.[36]
Plant growth regulators are the second category of common contaminants. During the cultivation of cannabis, a variety of chemicals such as fertilizers and pesticides can be used to encourage growth or reduce pests.[37] In 2017, a study of cannabis samples from licensed producers found that 18% of the samples showed the presence of pest control samples.[38] Users who consume cannabis contaminated by pesticides put themselves at risk for developmental issues, malignancy, neurological, reproductive, and endocrine disorders.[39]
The third category of contaminants is heavy metals. Heavy metals can be present in the soil or growing medium for cannabis, and unfortunately for users, cannabis plants are hyperaccumulators, meaning they can absorb high levels of heavy metals.[40] Contamination of heavy metals like lead, cadmium, arsenic, and mercury, can also occur during the processing of the drug or from cross-contamination with the metal components of electronic vaporizers.[41] Researchers have found that if a metal coil is present in a vaporizer, the coil leaches, or dissolves, metals like manganese and nickel into the product which could lead to exposure exceeding minimal risk levels.[42] Testing of cartridges has also shown metals like lead can leach from the cartridge into the liquid cannabis.[43] During a study of cartridge contamination, at least 50% of the liquid samples had some level of detectable lead.[44] Exposure to lead can cause a variety of health complications like psychosis, paralysis, muscular weakness, kidney damage, and brain damage.[45] In small doses, heavy metals may not result in health complications, but chronic exposure can lead to damage to the lungs, brain, kidney, liver, and other important organs.[46]
The last category of common cannabis contaminants is chemical solvents. The presence of solvents is intentional in the production of cannabis concentrates, as they are used during the extraction process to separate cannabinoid compounds from the plant.[47] These solvents, like ethanol and carbon dioxide, pose a risk to users since they can persist even in the final product.[48] A nonprofit organization, the U.S. Pharmacopeial Convention (USP), has created some guidance for states regarding fifty-nine solvents, detailing what concentration of each solvent is considered safe for human consumption.[49] However, two solvents found in cannabis concentrates, butane and propane, are not included in this list.[50] Research has shown that acute hypoxic respiratory failure can result from frequent use of butane hash oil, a type of cannabis concentrate that is produced using butane.[51]
To sell cannabis within a state, most states require producers to be licensed and for products in dispensaries to be tested for the contaminants listed above.[52] However, states disagree about which cannabis contaminants to test for and what levels of contamination are acceptable or safe for human consumption.[53] California is estimated to be the largest cannabis market in the United States and requires all cannabis products in the market to be tested for sixty-eight pesticides, twenty solvents, six microbes, four inorganics, and five mycotoxins.[54] State-licensed cannabis testing laboratories certify that products comply with regulations before being distributed to dispensaries.[55] California is considered the gold standard of testing requirements since the state’s test is so comprehensive.[56]
However, not all states meet California’s stringent standards for testing cannabis products. The discrepancies in testing are vast among states. A recent study by the Arizona Department of Health Services found no consensus standards amongst states for microbial testing.[57] Several different standards were used by states including, the American Herbal Pharmacopoeia (AHP), USP- Section 1111, USP- Section 2023, and some states even use their unique testing limits not found in any known standard.[58] Regarding heavy metals, all states that required metals testing included tests for arsenic, lead, cadmium, and mercury.[59] However, only four states tested for chromium, a metal that can contaminate cannabis as a result of the cultivation environment.[60]
Regarding solvent testing, the Arizona Department of Health Services noticed some states adopted the USP standard.[61] Some states did not have similar solvent limits to the USP, and it is unknown where most of those states’ limits originate from.[62] Oregon’s limit for both solvents and pesticides, however, was developed through the expertise of a technical committee designed to create specific standards for cannabis testing.[63] Concerningly, most states did not require herbicide testing, and the standards for pesticides, fungicides, and other growth regulators varied widely.[64] Overall, seventy-two pesticides were tested across the states, but the most commonly tested pesticides, Imidacloprid and Myclobutanil, were only tested in nineteen states.[65] The discrepancies in regulations across the different states become glaringly obvious when looking at reports that compile and compare the standards.
III. Discussion
The discrepancies in cannabis contamination regulations across the states present significant challenges to producers and health risks to consumers. While states like California, Arizona, and Oregon have implemented comprehensive standards and researched how best to protect users from contaminants, other states have far less stringent standards, contributing to inconsistencies in product safety. The lack of federal oversight leaves each state to determine its testing policies, further promoting conflicting or incomplete state regulations. States regularly turn to departments like the FDA and EPA for guidance and research on how to craft regulations.[66] Without input from these agencies, states must rely on either their research or observe what regulations other states are implementing. Ultimately, concerns about user health and safety are called into question as products deemed safe in one state may fail to test and be recalled in another.
To improve cannabis safety, states must start or continue researching the health and safety risks of contaminants and monitor how other states are regulating cannabis. There are very serious health repercussions for cannabis users if they ingest harmful levels of pesticides, heavy metals, microbial, or solvents. While there is a long list of common pesticides that appear across state regulations, even the most commonly regulated pesticides are not regulated in all states. This means that the appearance of a pesticide in one state might result in the product being recalled, but another state might not even test for that pesticide, exposing its residents who use cannabis to dangerous chemicals. States should begin by examining what pesticides are on the most commonly regulated pesticide list and research whether those pesticides pose a risk for their citizens and should be tested for.
For microbial and solvent testing, states should adopt either the AHP or USP standards as their guide. Independent organizations have provided adequate research in this area to serve as a basis for state regulations. If a state chooses not to follow these standards, it should disclose the research and rationale behind its alternative regulations, including studies on microbes and solvents in the state’s legal marijuana supply. Regarding heavy metals, chromium should be included in every state’s testing requirements. There have been several incidences in which the states that conduct tests for the metal have documented its appearance in cannabis products.[67] If a product contains metals like a metal coil or cartridge, it is recommended that the cannabis extract inside be tested over time to determine if there is leaching.[68] While more research, testing, and regulatory oversight may require increased state spending, the growing number of cannabis users suggests that these expenses should be a priority.
Currently, states must conduct their own research and make risk assessments on contamination levels in cannabis products. However, if cannabis is rescheduled to Schedule III, the federal government could provide guidance and implement nationwide regulations. This shift could help bridge the gaps left by states with lax regulations or contamination standards based on unknown data. With federal oversight, cannabis testing could become more standardized, ensuring that all cannabis products meet the same safety requirements regardless of state borders. This would provide greater assurance to both recreational and medical cannabis users, who could confidently consume products without concern for potential contaminants.
IV. Conclusion
The legalization of cannabis across multiple states has resulted in a complex and inconsistent regulatory landscape for contamination testing. While states like California have implemented rigorous testing standards, others have fewer comprehensive requirements, leading to discrepancies in the detection of microbial contamination, pesticides, heavy metals, and solvents. For the time being, states should re-examine their legislation and look to comprehensive regulators like California and Oregon. Including more pesticides and heavy metal chromium in the testing requirements and following a set standard for microbial and solvent testing like the USP would be a step in the right direction.
Moving forward, establishing a national framework or federal guidance for cannabis contamination testing would create uniformity and ensure that all cannabis products meet consistent safety standards. As the cannabis industry continues to expand and attract a broader consumer base, addressing these regulatory inconsistencies will be essential to protecting public health and ensuring consumer safety.
[1] What Percentage of Americans Smoke Marijuana, Gallup (Nov. 1, 2024), https://news.gallup.com/poll/284135/percentage-americans-smoke-marijuana.aspx.
[2] Id.
[3] 2025 Cannabis Policy Reform Legislation and Voter Measures, Marijuana Policy Project (Feb. 11, 2025), https://www.mpp.org/issues/legislation/key-marijuana-policy-reform/; State Medical Cannabis Laws, Nat’l Conf. of State Legis. (Feb. 1, 2025), https://www.ncsl.org/health/state-medical-cannabis-laws.
[4] Isreal Sepulveda, Marijuana Laws by State for 2025. Where is Marijuana Legal, Covercannabis.com (Mar. 5, 2025), https://covercannabis.com/blog/where-is-marijuana-legal/.
[5] Id.
[6] Laura E. Jameson et al., Comparison for State-Level Regulations for Cannabis Contaminants and Implications for Public Health, 130 Environmental Health Perspectives 1, 1-2 (2022).
[7] Sydney Lupkin & Brian Mann, How Safe is your Weed? Patchy Regulations May Leave Contaminants in the Weed Supply, NPR (Feb. 3, 2025), https://www.npr.org/2025/02/03/g-s1-46197/weed-marijuana-cannabis-safety-regulation.
[8] Id.; Jameson, supra note 6.
[9] Lupkin, supra note 7.
[10] About Cannabis Policy, Alcohol Pol’y Info. Sys., https://alcoholpolicy.niaaa.nih.gov/about/about-cannabis-policy (last visited Mar. 9, 2024).
[11] Id.
[12] Marijuana law in the United States: History of Marijuana Regulation in the United States, University of Georgia Law Library, https://libguides.law.uga.edu/marijuanalaw (Feb. 15, 2024).
[13] Id.
[14] About Cannabis Policy, supra, note 10.
[15] Marijuana law in the United States: History of Marijuana Regulation in the United States, supra, note 12.
[16] About Cannabis Policy, supra, note 10.
[17] Id.
[18] Id.
[19] Marijuana law in the United States: History of Marijuana Regulation in the United States, supra, note 12.
[20] About Cannabis Policy, supra, note 10.
[21] Leighann Thone & Elaina Rudder, Medical Marijuana Update 2025, Kan. Legis. Rsch. Dep’t (Dec. 18, 2024), https://klrd.gov/2024/12/18/medical-marijuana-update-2025/.
[22] Id.
[23] Id.
[24] If Weed is Rescheduled, Does That Mean It Is Now Federally Legal? (And Other Questions You Were Afraid to Ask), Cannabis.net (Oct. 8, 2023), https://cannabis.net/blog/news/if-weed-is-rescheduled-does-that-mean-it-is-now-federally-legal-and-other-questions-you-were-af?utm.
[25] Dorothy C. Kafka, Legal Effect of Marijuana Rescheduling on FDA’s Regulation of Cannabis, Cong. Rsch. Serv. 5-6 (Sept. 16, 2024), https://crsreports.congress.gov/product/pdf/LSB/LSB11227.
[26] Nate Seltenrich, Cannabis Contaminants: Regulating Solvents, Microbes, and Metals in Legal Weed, 127 Environmental Health Perspectives 8 (2019).
[27] Id.
[28] Id.
[29] Id.
[30] Laure M. Dryburgh et al., Cannabis Contaminants: Sources, Distribution, Human Toxicity, and Pharmacologic Effects, 84 British Clinical Pharm. Soc’y 1, 2 (2018).
[31] Id.
[32] Seltenrich, supra note 26.
[33] Knowledge Synthesis Contamination of Cannabis Products for Human Consumption, Michael G. DeGroote Cent. for Med. Cannabis Rsch., https://cannabisresearch.mcmaster.ca/wp-content/uploads/2023/02/mgdcmcr_cannabiscontamination.pdf (last visited Mar. 9, 2025).
[34] Id. at 2; Seltenrich, supra note 26, at 3.
[35] Knowledge Synthesis Contamination of Cannabis Products for Human Consumption, supra note 33.
[36] Dryburgh, supra note 30, at 3.
[37] Knowledge Synthesis Contamination of Cannabis Products for Human Consumption, supra, note 33, at 3-4.
[38] Id.
[39] Dryburgh, supra note 30, at 4.
[40] Knowledge Synthesis Contamination of Cannabis Products for Human Consumption, supra, note 33, at 4.
[41] Id.
[42] Seltenrich, supra note 26, at 4-5.
[43] Id.
[44] Id.
[45] Monisha Jaishankar et al., Toxicity, Mechanism and Health Effects of Some Heavy Metals, 7 Interdisc. Toxicology 60, 68 (2014).
[46] Id.
[47] Should You Worry About Residual Solvents?, Encore Labs (May 1, 2020), https://encorelabs.com/should-you-worry-about-residual-solvents/.
[48] Seltenrich, supra note 26, at 2-3; Should You Worry About Residual Solvents?, supra, note 47.
[49] Id.
[50] Id.
[51] Should You Worry About Residual Solvents?, supra, note 47.
[52] Ben Warren & Julie Wernau, Legal Marijuana Contains Dangerous Mold. States Approve it Anyway., The Wall St. J. (Oct. 17, 2024), https://www.wsj.com/health/healthcare/marijuana-mold-contaminants-safety-a172c230.
[53] Lupkin, supra note 7.
[54] Jameson, supra note 6, at 2.
[55] Id.
[56] Harrison Bard, Understanding California’s Regulatory Landscape & Comprehensive Testing Requirements, TheCannabisIndustry.org (Jan. 30, 2024), https://thecannabisindustry.org/member-blog-californias-gold-standard-navigating-cannabis-testing-regulations/.
[57] Summary of 50 State Review for Medical Marijuana Laboratory Testing Advisory Committee, Ariz. Dep’t of Health Serv., https://www.azdhs.gov/documents/licensing/medical-marijuana/testing-advisory-council/50-state-review.pdf (last visited Mar. 9, 2025).
[58] Id.
[59] Id.
[60] Id.
[61] Id.
[62] Id.
[63] Id.
[64] Id.
[65] Id.
[66] Pesticide Labeling Questions and Answers, EPA (May 13, 2024), https://www.epa.gov/pesticide-labels/pesticide-labeling-questions-answers.
[67] John McPartland & Kevin McKernan, Contaminants of Concern in Cannabis: Microbes, Heavy Metals and Pesticides, Cannabis sativa L. – Botany and Biotechnology 457, 466-467 (2017).
[68] Seltenrich, supra note 26, at 5.
Cover Photo generated with Google Gemini AI generator.
