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January 15, 2021 Feature

Hemp or Marijuana? The Importance of Accurate and Reliable Forensic Analysis to the Fair Administration of Justice

By Lynn Garcia and Peter Stout

On December 20, 2018, the Agriculture Improvement Act of 2018 legalized the industrial production of hemp nationwide while simultaneously removing hemp from the Controlled Substances Act. Hemp was reclassified as an agricultural product, and the U.S. Department of Agriculture (USDA) was charged with publishing regulations to govern the industry. The federal legislation differentiated hemp from marijuana by setting a THC threshold concentration of 0.3 percent.

Cannabis contains many different chemical compounds known as cannabinoids. Delta-9 tetrahydrocannabinol (THC) is one type of chemical compound derived from cannabis and is the cannabinoid molecule that has long been recognized as the main psychoactive ingredient (the substance that causes people who use marijuana to feel high).

The federal legislation delegated to states and Indian tribes through their departments of agriculture the broad authority to regulate and limit the production and sale of hemp products within their borders.1 For example, Texas enacted the Texas Hemp Bill, effective September 1, 2019, with the same THC limit as the federal law (0.3 percent) and removed hemp from the definition of “controlled substance” and “marijuana.”2

Under the Texas Hemp Bill (H.B. 1325) and many similar bills adopted in state legislatures around the country, marijuana and tetrahydrocannabinol, or THC (excluding the limited THC in hemp), remain illegal substances. What changed under Texas law, similar to the federal legislation, is that “hemp” is now excluded from the definition of “controlled substance” and “marijuana.”

What’s the Difference Between Hemp and Marijuana?

Hemp and marijuana both come from the cannabis plant. Different parts of the plant have different THC concentrations, and various factors may impact whether a particular plant sample exceeds the statutory THC limit of 0.3 percent. Historically, the stalks of the cannabis plant had very low levels of THC, while the leaves and flowers (buds) had higher levels of THC. In fact, this was the basis of the historical definition of marijuana, which excluded certain parts of the Cannabis sativa L. plant such as the mature stalks. However, selective breeding and growing conditions have produced cannabis plants with low levels of THC throughout the entire plant. In addition, decision-making during the harvesting process may impact THC concentration. For example, if a hemp farmer waits too long to harvest, the THC in the crop may exceed the legal threshold. Legislative and administrative safeguards have been established to ensure plant material from agricultural producers is compliant with the THC cutoff established in the law. The challenge is that analyzing the THC concentration in plants from a harvest in an agricultural setting is a far more straightforward process than analyzing the types of evidentiary items typically confiscated by law enforcement and submitted to a forensic laboratory for analysis.

As a result of this continuous evolution of both hemp and marijuana products, it is clear that forensic testing is the only way to truly know if a cannabis plant or parts of the plant such as stalks, stems, leaves, or buds can be considered as hemp or marijuana.

Case Example: 3,000 Pounds and 30 Days

In December 2019, a Texas state trooper conducted a traffic stop of a U-Haul truck and observed what appeared to be over 3,000 pounds of marijuana. The driver was arrested and charged with a federal felony in the Northern District of Texas. The trooper identified the substance as marijuana based on his training and experience. One month later, the driver was released from custody and the criminal case was dismissed after forensic testing revealed the plant substance was hemp.

Case Example: If It Smells Like a Skunk . . .

Historically, one of the most common justifications for a warrantless vehicle search has been the “odor of marijuana.” In Childress v. State,3 a trooper stopped a vehicle for a traffic violation and smelled the odor of marijuana coming from the vehicle. The trooper recovered a handgun from the vehicle, and the defendant was charged with unlawfully carrying a weapon while engaged in criminal conduct, namely, possession of marijuana. At trial, proof that the substance was marijuana consisted of the officer’s opinion that the substance was marijuana based on his training and experience.

The court cited established case law holding that law enforcement officers are not required to be experts in identifying marijuana to testify regarding their observations. “[M]arihuana is easily identifiable; it does not take an expert to identify its odor.”4 The court noted the defense’s challenge to the continued viability of this holding in the wake of hemp legalization. The court, however, did not address the argument because the defendant’s arrest occurred before the change in the law. While waiting for courts to resolve this particular issue, many law enforcement agencies are taking a more holistic approach to justifying warrantless searches, including emphasis on the behavior of the vehicle’s occupants.

How It Worked Before Hemp Was Legalized

Before hemp was legalized, laboratories reported a positive result if cannabinoids were present. When no cannabinoids were detected, the laboratory reported no controlled substance. The laboratories were not required to quantitate the THC, for example, to identify the exact amount of THC in the evidentiary sample. In addition, before hemp was legalized, law enforcement officers could testify an item was consistent with marijuana based on their years of experience and other indicators such as smell. But hemp and marijuana come from the same plant. They smell the same. Once harvested, they largely look the same. This new reality presented challenges for law enforcement and prosecutors alike.

When the federal farm legislation passed, most crime labs in the country—including but not limited to the U.S. Drug Enforcement Administration (DEA)—knew they did not have the ability to quantitate marijuana in every case and would need to find a way to accurately distinguish between hemp and marijuana efficiently and in a cost-effective way. They knew quantitation was far more complex and costlier than simply identifying the presence or absence of cannabinoids. They knew it would take time to get new methods validated and implemented. And they knew that simply applying methods used in the agriculture industry would not be sufficient to address forensic casework samples.

While labs were working hard to respond to the needs of the criminal justice system, prosecutors took varying positions about how to proceed with misdemeanors in particular. Some dismissed large numbers of misdemeanors. Others insisted marijuana prosecutions would continue as they always had. Felony prosecutions waited on decisions regarding whether testing should be outsourced to private laboratories with existing quantitation capabilities. Texas is a large and diverse state with 254 counties. The elected district and county attorneys of those counties have adopted different policy positions on marijuana prosecution depending on the particular resources and priorities in their communities.

Analytical Challenges: The Difference Between Agricultural Testing and Forensic Testing

The cannabis plant is very challenging material to analyze. Over 100 related cannabinoids are contained within the plant. In an agricultural setting, the cannabinoids present in plant material are somewhat predictable and relatively easy to differentiate. This greatly facilitates and simplifies regulatory testing using agricultural crops. In a forensic setting, however, it is common for additional compounds (including synthetic cannabinoids or other substances) to have been added to the plant after it was harvested. Just as a forensic laboratory cannot assume that a pill that clearly looks like a manufactured legal pharmaceutical is what it appears to be, a forensic laboratory must assume that any cannabis product may in fact be something partly or wholy other, including not having any detectable controlled substances. This greatly increases the complexity of the analysis because the scope of testing is not just limited to the natural cannabinoids that are present in cannabis. Many of these compounds have very similar chemical structures and behavior. Differentiation of these structurally similar drugs is complex, requiring sophisticated instrumentation with very specific detectors. The use of analytical techniques that lack high discriminating power increases the risk of misidentifying something that is not delta-9-THC as delta-9-THC (thus resulting in a false positive). Texas laboratories have already received reports of false positives from crime labs in other states that attempted to incorporate technologies similar to those used in agricultural testing.

Differentiation of Hemp from Marijuana Using a Qualitative Decision Point Assay

Recognizing that full quantitation would be unworkable from both a time and a cost standpoint in the vast majority of seized-drugs cases involving suspected marijuana, forensic science service providers sought to develop analytical methods to ensure they could reliably and accurately distinguish hemp from marijuana without paralyzing the criminal justice system.

The DEA was the first to deploy a “decision point” gas chromatography/mass spectrometry (GC/MS) assay as part of their analytical scheme to differentiate hemp from marijuana. This approach, which has since been successfully implemented in other laboratories, was the subject of an interlaboratory study, facilitated by Sam Houston State University (SHSU) and the Texas Forensic Science Commission.

In late February 2020, the National Institute on Drug Abuse (Drug Supply Program) provided marijuana plant material for a collaborative study between SHSU, Houston Forensic Science Center (HFSC), Harris County Institute of Forensic Sciences (HCIFS), and the Texas Department of Public Safety (DPS) Crime Laboratory Service.

Each of the collaborating laboratories selected an administrative threshold in plant material of 1 percent Δ9-tetrahydrocannabinol (Δ9-THC) by weight rather than the 0.3 percent established by law. In addition to this safeguard, the analytical approach is likely to underestimate the total Δ9-THC due to extraction efficiencies and decarboxylation rates less than 100 percent. This approach is designed to prevent false-positive results and increase specificity at the expense of sensitivity. Assay specificity (the ability to correctly identify a known negative sample) was 100 percent across all sites, and assay sensitivity (the ability to correctly identify a known positive sample) was 94 percent.

While the Texas method was based in significant part on the DEA approach, there are some differences between the DEA’s analytical scheme and the Texas method, including but not limited to the fact that the Texas approach does not include a color reaction test as a component of the analytical scheme.5

Even with all the work the DEA and Texas labs have done to validate semi-quantitative methods, the methods developed to date have some important limitations:

  1. The methods cannot currently be used on waxes, dabs, edibles, oils, vape materials, or anything else that is not a plant.
  2. They measure whether a plant material has more or less than 1 percent THC but do not provide a specific concentration.
  3. More precise testing currently requires full quantitation, which is done in far fewer laboratories and in some cases may need to be outsourced to private laboratories at costs that are not insignificant for many local jurisdictions.
  4. The new methods take far longer than previous analysis, which only determined whether a product was cannabis and if it had cannabinoids, not a specific one or how much. This increases turnaround times for all laboratories absent additional resources dedicated to the effort.

But the Law Says 0.3 Percent Is the Legal Threshold? Why Are So Many Labs Using 1 Percent?

The vast majority of laboratories have chosen 1 percent or higher as an “administrative threshold” for reporting instead of the 0.3 percent commonly referenced in legislation. Some labs have chosen 2 percent, and the U.S. Army Laboratory uses 4 percent. The justification for administrative cutoffs that exceed statutory cutoffs is that (1) laboratories want to be conservative in their reporting in light of the analytical challenges described above and (2) their experience in analyzing marijuana cases shows that the vast majority of marijuana samples that come into the laboratory contain THC levels far higher than 1 percent. Indeed, most laboratories are accustomed to seeing levels higher than 10 percent.

Clarity Still Needed on a Number of Legislative Questions

Understandably, Texas, and many other states, based H.B. 1325 on the Federal Farm Act that legalized hemp nationally. However, the statutory language created some interpretation challenges that remain to this day.

How Should Laboratories Interpret the Term “Dry Weight”?

Applicable law currently states the products should be analyzed based on “dry weight.” But what does this mean? At a crime laboratory, marijuana plants are often dried to prevent molding and preserve the integrity of the evidence. Considering that the drier the plant is the higher the percentage of THC will appear, how dry is dry? For example, suppose a plant is harvested with 0.29 percent THC. This plant material is seized by law enforcement and sent to a forensic lab for analysis. The lab dries the material at 50C for several days. This process has the potential to not only decarboxylate more THCA to THC, but it also reduces the weight by half. Now the material that began as 0.29 percent becomes illegal in the hands of the forensic lab. Also, what does dry weight mean in a nonplant product, such as an oil, a wax, or an edible?

Narrow Use of Cannabis sativa L. Term Leads to Confusion

Currently, hemp and marijuana are both narrowly defined as products of the Cannabis sativa L. plant, and the THC concentration is based on the specific delta-9 isomer. However, there is no real difference between Cannabis sativa and other varieties such as Cannabis indica, for example. So, by defining the law so narrowly, questions may arise about the legality of products that purport to be from the C. indica variety regardless of THC concentration. And what about products that arrive with delta-8, delta-10, and other THC isomers that are apparently synthetic? Are those legal because the definition in the law is narrowly confined to delta-9-THC? These are things we often see in the crime laboratory and currently, due to the definition in the law, the control status of these products is unclear. This is especially concerning because many of the items may lead to substantial impairment.

The definition of hemp as the Cannabis sativa L. plant or a product of that plant with a THC concentration of 0.3 percent or less presents a whole other set of problems when we deal with nonplant materials, such as vape products and edibles. Clearly, the Texas legislature (and other legislatures adopting similar language) did not intend to legalize marijuana or any of the impairing qualities of that drug. However, by subscribing THC concentration as a percent in the world of nonplant products, the result is in fact the ability to legally buy and sell impairing products. For example, a 100g cookie that has 10 milligrams of THC will have a concentration of 0.01 percent, far less than 0.3 percent, making this “hemp.” But this would constitute a “serving” of THC under Colorado law and could still be potentially impairing to an individual who consumed that entire cookie.

The law currently states that CBD that originates from legally grown hemp is legal, while CBD that is derived from a marijuana plant is illegal. However, crime laboratories—and really no laboratory—can know whether CBD in a nonplant product came from a hemp or a marijuana plant.

What About Requiring Documentation for Possession?

The Texas Agriculture Code implies legislative intent was that only licensed growers and manufacturers should be permitted to possess the cannabis plant. This means the general public and unlicensed retailers should not have it. Other states (e.g., Kentucky) have clarified that a person or entity may not possess a cannabis plant without appropriately issued documentation.

There Is No Easy or Inexpensive Answer for Edibles

Crime laboratories will need new and different instrumentation to establish testing methods for nonplant materials, especially for edibles. Currently, most publicly funded laboratories do not have a validated and approved method for full quantitation, which is what would be needed for edibles. Financial and human resource needs here (including instrumentation) are significant. Unlike e-liquids and cannabis plant material, edibles come in many different forms (fat- or lipid-rich chocolates, to cookies/brownies, gummies, and hard candy). Test methods for edibles require extensive sample clean-up (extraction protocols) to separate cannabinoids and other drugs from the food matrix itself. Failure to properly isolate the compounds of interest from the food matrix can result in interferences that could negatively influence the reliability of the test and the concentration of drug. Extensive extraction and sophisticated instrumentation are required to quantify delta-9-THC in edibles and separate it from structurally similar compounds.

Potential Solutions


Public crime laboratories must have adequate resources to function effectively. The analysis required to differentiate between hemp and marijuana is complex, time consuming, and expensive. It diverts resources from other equally important endeavors, including analysis of other drugs such as opioids and methamphetamine. Flexibility in this funding is key. The additional resources would allow crime laboratories to buy the most appropriate instrumentation needed to test nonplant materials or to outsource to private laboratories where that approach is more efficient.

Legislative Clarifications Needed in Many States

Dry Weight. For plant materials, differentiating between hemp and marijuana products in the law may resolve the problem. For example, the legislation could be tweaked to clarify that forensic laboratories will use the weight “as received” and dry materials for the purposes only of preserving the integrity of the evidence.

Broaden Definition of Cannabis Plant to Avoid Confusion. Cannabis plants have been so cross cultivated over the years as to make the differences between the varieties, such as C. sativa and C. indica, almost irrelevant. Most legislation, however, does not account for this, and the narrow definition, likely inadvertently, allows for an argument to be made that an “indica” or “ruderalis” plant, regardless of THC concentration, may in fact be legal. For all involved, especially crime laboratories, broadening the definition to simply define marijuana and hemp as the cannabis plant or derivatives of cannabis plants would be far more effective.

Clarifying the Legal Status of THC Isomers Beyond Delta-9. Crime laboratories are also seeing more products that have isomers of THC other than delta-9. This makes it difficult to determine whether an item is controlled or uncontrolled if legality is based solely on the presence and concentration of delta-9-THC. To overcome this problem, laws should be updated to clarify the legal status of other THC isomers regardless of the presence or absence of delta-9-THC.

Include “Dosages” or “Serving Sizes” for Edibles. In states like Texas where marijuana is illegal, edible hemp products should likely not have more than 1 milligram of THC per labeled serving if the goal is to keep impairing THC products illegal. This would both assist manufacturers attempting to create hemp-based products that have nonimpairing, low-THC concentrations and greatly help crime laboratories that are essentially being asked to determine whether the amount of THC in a sample could cause impairment. A Texas-accredited laboratory recently demonstrated that 2 × 5g gummies containing 0.15 percent delta-9-THC constitute a potent oral dose. The dose should be more important than the percent of THC for edibles.

Seed-to-Sale Tracking Mechanisms. Finally, the only real way to know whether a product originates in a hemp or a marijuana plant is to have a workable tracking mechanism in place. Most legislation requires paperwork for transport, but once a product has been distributed to a store or a retailer, there is no clear indication whether the item was derived from hemp or marijuana. A tracking mechanism could require specific labeling on manufactured items. It could also include a requirement for people to have “proof of possession” detailing the origin of the item. Failure to have this labeling and proof of possession would be a fineable offense.

In closing, cannabinoids have never been and never will be easy to analyze. The entire criminal justice system understands the need to create a mechanism for farmers to legally grow hemp and manufacturers to produce and distribute items derived from those plants. At the same time, stakeholders must work together to ensure forensic laboratories are able to provide criminal justice stakeholders with reliable and valid analytical results in support of the fair administration of justice.


1. See State Industrial Hemp Statutes, Nat’l Conf. of State Legislatures (Apr. 16, 2020),, for an overview of state statutes.

2. Hemp is defined as “the plant Cannabis sativa L. and any part of that plant, including the seeds of the plant and all derivatives, extracts, cannabinoids, isomers, acids, salts of isomers, whether growing or not, with a delta-9 tetrahydrocannabinol concentration of not more than 0.3 percent on a dry weight basis.” H.B. 1325, 86(R) Legis. Sess. (Tex. 2019).

3. 2020 Tex. App. LEXIS 1170 (Feb. 12, 2020).

4. Id. at *6.

5. Specific questions regarding the method developed in Texas, including a discussion of validation data from laboratories that participated in the interlaboratory study discussed here, may be directed to the Texas Forensic Science Commission at [email protected].

The material in all ABA publications is copyrighted and may be reprinted by permission only. Request reprint permission here.

Lynn Garcia


Lynn Garcia is general counsel at the Texas Forensic Science Commission. 

Peter Stout


Peter Stout is chief executive officer at the Houston Forensic Science Center and president of the Texas Association of Crime Laboratory Directors.