The growing use of cannabis, both medically and recreationally, raises questions about its impact on standard laboratory testing. “Blood work” refers to common panels used by healthcare providers to assess overall health, screen for disease, and monitor organ function. Routine clinical tests, such as a Complete Blood Count (CBC) or a Comprehensive Metabolic Panel (CMP), measure biological markers like cholesterol, glucose, and liver enzymes. Because cannabis compounds interact with the body’s biological systems, they can potentially influence the accuracy and interpretation of these results.
How Cannabis Metabolites Show Up in Testing
Standard medical blood panels generally do not include screening for cannabis unless a specific drug test is explicitly ordered. The active psychoactive compound, delta-9-tetrahydrocannabinol (THC), is fat-soluble and rapidly metabolized by the liver. Blood tests primarily target active THC, which is typically detectable for only a few hours up to a couple of days after consumption, making them useful for determining recent use or current impairment.
In contrast, most traditional drug screenings, such as urine tests, look for an inactive metabolite called THC-COOH. This metabolite is stored in fat cells and gradually released, remaining detectable for much longer periods—from several days after a single use to weeks or months in chronic users. The presence of this inactive metabolite does not correlate with current impairment, unlike active THC in the blood.
Specific Effects on Common Clinical Markers
Cannabis use can introduce variability into the results of non-drug-related clinical blood markers, especially with chronic or heavy consumption.
Glucose Metabolism
Studies examining glucose metabolism offer conflicting results. Some large-scale surveys suggest cannabis users have lower levels of fasting insulin and less insulin resistance. However, the acute impact of cannabis on appetite can lead to immediate blood sugar fluctuations that may skew a fasting glucose test.
Lipid Panel
The effects on the lipid panel, which measures cholesterol and triglycerides, are not uniform across scientific literature. Some research indicates chronic users may have lower levels of high-density lipoprotein (HDL) cholesterol. Other studies suggest persistent use may be associated with improved lipid profiles, including lower triglycerides and higher HDL levels. Variability in findings is often due to differences in consumption method, frequency, and lifestyle factors.
Liver Function
Liver function tests, which measure enzymes like aspartate aminotransferase (AST) and alanine aminotransferase (ALT), can also be affected. Chronic cannabis use has been correlated with mild, transient elevations in these liver enzymes in some individuals. This effect is often more pronounced when cannabis is used in combination with other substances, such as alcohol.
Complete Blood Count (CBC)
The components of a Complete Blood Count (CBC) may show minor changes in heavy users. Some evidence indicates a modest association between regular cannabis use and a slight increase in the total white blood cell (WBC) count, especially neutrophils. This minor elevation may be a generalized inflammatory response, particularly if the cannabis is inhaled through smoking.
Preparing for Accurate Blood Test Results
The most important step a patient can take to ensure accurate blood work is to be fully transparent with the ordering physician about cannabis use. Disclosing the frequency, method, and dosage allows the provider to correctly interpret any borderline or unexpected results, such as those related to liver enzymes or blood sugar.
To minimize the acute effects of cannabis on clinical markers, it is recommended to abstain from use for 24 to 72 hours before any non-urgent laboratory testing. Acute effects on glucose and white blood cell count can be reduced by avoiding consumption in the hours leading up to the blood draw. Patients must also adhere to specific fasting instructions provided for tests like lipid panels or fasting glucose.
Drug Interactions
Cannabis compounds, notably THC and cannabidiol (CBD), are metabolized by the Cytochrome P450 enzyme system in the liver, the same pathway used by many prescription drugs. This can lead to drug-drug interactions where cannabis inhibits the metabolism of other medications, potentially increasing their concentration in the blood. This interaction is a factor for patients undergoing therapeutic drug monitoring for drugs with a narrow therapeutic index, such as blood thinners or anti-epileptic medications, requiring careful adjustment and monitoring.