About Testing for Marijuana in Blood

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According to Drug Detection Laboratories Inc., blood testing procedures for cannabis provide information that reveals if an individual is under the influence of marijuana. This plant-based substance contains THC, the intoxicating chemical element of cannabis. Marijuana can remain in the bloodstream for up to four hours after use. Individuals who use marijuana frequently have longer detection periods, due to the accumulation of THC in their bloodstream.


According to NARCONON International, non-medical use of marijuana to achieve euphoria dates back to A.D. 500. Chinese medical writings from 2737 B.C. note its medicinal use. Then, in 1545, the Spanish introduced marijuana to the United States, where it became a commercial crop with tobacco. Marijuana was grown for use as fiber for clothing until it was replaced by cotton in the 1800s. Marijuana was prescribed during this same period as a medicine for labor pain, nausea and rheumatism symptom relief. The earliest history of specific drug legislation was 1914. The Harrison Act, according to the Drug Library website, made non-medical use of drugs illegal. However, sophisticated testing tools were not developed until the late 1950s.

Testing Identification

The Forensic Toxicology Specialists report that blood-testing tools identify cannabinoids, or the chemical compound 11-nor-9-carboxy-delta-9 tetrahydrocannabinol, the major psychoactive ingredient in cannabis. The National Organization for The Reform of Marijuana Laws states that blood screening detects the presence of immediate use of illicit drugs. THC only remains detectable in the bloodstream of marijuana users for a few hours. Therefore, blood tests are administered in the workplace after an accident because of its ability to determine use within 12 to 24 hours.


Urine testing is a more effective testing tool for THC in the body than blood testing. Blood testing, however, can reveal current intoxication levels better than urine testing as indicated by Forensic Toxicology Specialists with Drug Detection Laboratories Inc. Urine testing determines use within approximately the last 20 days, depending on frequency of use. Marijuana is the most commonly used illegal drug in the world, notes the National Highway Traffic Safety Administration.


Although testing for marijuana in the blood is not as cost effective, does not determine frequent use, and if errors occur during testing may not be reliable, marijuana in the bloodstream does alert employers, government authorities and law enforcement of the recent use of illicit drugs. In addition, the Drug Policy Alliance suggests the effects of cannabis use include euphoria, sedation, sleepiness, ataxia and short-term memory impairment. The physiological effects are red eyes and increased pulse and blood pressure. The effects of the recreational use of this illegal plant are counterproductive in employment settings and vehicle operation. Therefore, blood-testing procedures can protect employers and the community.

Expert Insight

According to a 1996 Federal Bureau of Investigation report, marijuana arrests in the United States doubled from 1991 to 1995. During this time, approximately 500,000 people were arrested for marijuana offenses with 86 percent arrested for marijuana possession. The FBI notes that tens of thousands of people are currently imprisoned for marijuana offenses. In addition to jail time, many are punished with fines, personal property seizure, driver's license revocation and terminated employment.