The key to understanding cannabis use lies not in the plant itself, but in our own biology.
When a person uses cannabis, whether for therapy or recreation, its compounds embark on a complex journey through the body. Scientists can track this journey by analyzing biological fluids, a field that has become crucial for everything from diagnosing impairment to validating medical treatment. This process relies on sophisticated technology to find minute chemical clues in a sea of biological noise, revealing not just if someone used cannabis, but often when, how much, and what type.
For researchers and toxicologists, this isn't about a simple positive or negative test. It's about deciphering the intricate story told by cannabinoids and their metabolites in blood, urine, and oral fluid.
As cannabis laws and medical applications evolve, the precision of this science becomes ever more vital for public safety, healthcare, and the legal system.
To understand how we detect cannabis in the body, one must first understand what happens after it is consumed. Cannabis contains over 545 different compounds, with more than 100 classified as cannabinoids1 . The most famous is delta-9-tetrahydrocannabinol (THC), the primary psychoactive component.
The method of consumption plays a significant role in this journey. When smoked or vaporized, THC enters the bloodstream through the lungs, appearing in plasma within seconds1 . When ingested orally, as in edibles, the onset is slower, and the compounds are processed through the digestive system, leading to a different metabolic profile.
Finding these cannabinoid markers is a two-step process, typically starting with a rapid screening test followed by a confirmatory analysis. This rigorous approach is necessary because false positives and negatives can have serious consequences.
Initial tests often use immunoassays, such as the enzyme multiplied immunoassay technique (EMIT)1 . These tests are fast and can handle many samples, but they can be fooled by compounds with a similar structure to the target. A positive immunoassay result is always just a preliminary finding.
For definitive results, labs turn to advanced instrumental techniques. Gas chromatography-mass spectrometry (GC-MS) and liquid chromatography-mass spectrometry (LC-MS) are the gold standards1 . These separate the complex biological mixture and provide a unique molecular fingerprint for each compound.
Before analysis, the sample must be prepared. Techniques like liquid-liquid extraction (LLE) or solid-phase extraction (SPE) are used to isolate the cannabinoids from the biological matrix and remove interfering substances1 . The choice of method depends on the target analytes; for instance, the pH must be adjusted because THC is neutral, while its metabolite, THC-COOH, is acidic6 .
While most routine testing focuses on THC and its major metabolites, the cannabis plant itself is a treasure trove of undiscovered chemicals. A groundbreaking experiment from Stellenbosch University shows how advanced technology is revealing this hidden complexity.
In 2025, analytical chemists made a surprising discovery in cannabis leaves, which are often discarded as waste. Using a powerful technique known as comprehensive two-dimensional liquid chromatography coupled with high-resolution mass spectrometry, they identified 79 different phenolic compounds across three cannabis strains9 .
The analysis was a success. Of the 79 phenolic compounds identified, 25 had never before been reported in cannabis9 . Most excitingly, 16 of these new compounds were tentatively identified as flavoalkaloids, a very rare class of plant compounds that combine structural features of flavonoids and alkaloids9 .
| Category of Compound | Number Newly Identified in Cannabis | Potential Significance |
|---|---|---|
| Flavoalkaloids | 16 | Rare in nature; unknown biomedical potential |
| Other Phenolics | 9 | Could have antioxidant, anti-inflammatory properties |
| Total New Compounds | 25 | Highlights vast untapped chemical diversity |
The discovery of flavoalkaloids, found mainly in the leaves of just one strain, highlights the immense and untapped chemical diversity of the cannabis plant. It suggests that "waste" material like leaves could hold valuable new compounds with potential biomedical applications, opening new doors for future drug development and research9 .
The analysis of cannabinoids, whether in plant material or biological fluids, requires a suite of specialized tools and reagents. The following table details some of the key components used in modern laboratories.
| Reagent / Material | Function in Research |
|---|---|
| Organic Solvents (e.g., ethanol, hexane) | Used in extraction to dissolve and separate cannabinoids from the plant or biological matrix1 3 . |
| Solid-Phase Extraction (SPE) Cartridges | Used for sample clean-up to isolate cannabinoids and remove impurities from complex biological fluids like blood or urine1 . |
| Deuterated Internal Standards | Added to samples before analysis; these are cannabinoids with a slightly different mass used to calibrate mass spectrometers and ensure quantitative accuracy1 . |
| LC-MS Grade Solvents | Ultra-pure solvents for liquid chromatography to prevent instrument contamination and maintain consistent performance9 . |
| Immunoassay Reagents | Antibody-based solutions used in rapid screening tests to initially detect the presence of cannabinoid classes1 . |
The ability to precisely measure cannabinoids in biological fluids is more than an academic exercise; it has profound implications for society.
Cannabis is the most frequently detected drug in Driving Under the Influence of Drugs (DUID) cases1 . Accurate testing helps law enforcement and the legal system identify impaired drivers, making roads safer.
For patients using medical cannabis, monitoring levels can help ensure proper dosing and check for potential interactions with other medications.
Drug testing in workplaces, child custody cases, and drug-facilitated crimes often relies on the precise data generated by these analytical methods1 .
| Specimen | Detection Window | Primary Use & Advantages |
|---|---|---|
| Urine | Days to weeks | Most common for workplace testing; detects inactive metabolite (THC-COOH) indicating past use. |
| Blood | Hours | Best for determining recent impairment; measures active THC. |
| Oral Fluid | Hours | Growing use in roadside testing; non-invasive and correlates with recent use. |
| Hair | Months | Longest detection window; provides history of chronic use. |
The science of cannabinoid analysis continues to advance. Researchers are working to develop better breathalyzers for roadside testing and to identify more specific markers of recent use to better distinguish between recent impairment and past consumption6 .
As the cannabis industry grows and new compounds like the flavoalkaloids are discovered, the analytical toolkit will continue to evolve.
This ongoing refinement ensures that our understanding of cannabis use keeps pace with its changing legal and medical landscape, providing the critical data needed to make informed decisions in the clinic, the laboratory, and the courtroom.