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How Long Does Marijuana Show Up In a DUI Blood Test?

Posted on July 10, 2023

With driving under the influence (DUI) being a serious offense, it is crucial to know that marijuana can be detected in a blood test over 12 hours after consumption. If you are a frequent user, the drug can be detected for up to a week.

Detection Time Frames

While detection times can vary from person to person, marijuana can generally be detected in a standard blood test for the following periods:

  • Occasional use (1-3 times per week): Up to 3 days
  • Moderate use (4-5 times per week): Up to 5-7 days
  • Regular use (daily): Up to 1-2 weeks
  • Chronic use (multiple times daily): Up to 2-4 weeks or longer

Marijuana Metabolism and Detection

When marijuana is ingested, the active compound responsible for its psychoactive effects, tetrahydrocannabinol (THC), is absorbed into the bloodstream. THC levels in the blood peak rapidly within minutes after inhalation or ingestion and then start to decline. However, THC’s byproducts, known as metabolites, can linger in the body for much longer periods.

The primary metabolite of THC commonly tested in blood tests is called 11-nor-delta-9-tetrahydrocannabinol-9-carboxylic acid (THC-COOH). This metabolite is not psychoactive but is used as an indicator of recent marijuana use.

Factors Affecting Detection Time

Several factors can influence how long marijuana stays detectable in a DUI blood test:

Frequency of use

Individuals who consume marijuana regularly may have THC metabolites present in their blood for an extended period compared to occasional users.


Higher THC concentrations in marijuana products, such as edibles or concentrates, can lead to a prolonged detection window.


Variations in metabolism among individuals can impact how quickly the body eliminates THC and its metabolites.

Body fat percentage

THC and its metabolites are lipid-soluble, meaning they tend to accumulate in fat cells. People with higher body fat percentages may retain THC metabolites for longer.


Staying well-hydrated may help to flush out THC and its metabolites more rapidly.

Are Blood Tests Reliable Evidence in Marijuana DUI Cases?

The reliability of blood tests as evidence in marijuana DUI cases in Colorado can be a contentious issue due to the complexities surrounding marijuana detection and impairment. Unlike alcohol, which has a relatively predictable relationship between blood alcohol concentration (BAC) and impairment, THC’s effects on individuals can vary significantly. Some individuals may be impaired at lower THC levels, while others may not show impairment at higher levels.

Therefore, the argument can be made that blood tests are unreliable evidence as they cannot accurately determine the level of impairment at the time of driving. Someone who legally consumed marijuana days before driving but is no longer impaired could still be charged with a DUI based solely on the presence of THC in their system.

Potential Defenses to Marijuana DUI Blood Tests

Challenging the blood test is a common strategy used to defend individuals charged with marijuana DUI offenses. Potential grounds include:

Lack of Correlation Between THC Levels and Impairment

A lawyer may argue that THC levels in the blood do not necessarily correspond to impairment, highlighting the lack of a direct and reliable relationship between THC concentration and impairment.

Standard Field Sobriety Test Performance

If you performed well on standardized field sobriety tests and showed no obvious signs of impairment at the time of the traffic stop, your attorney may use this evidence to challenge the reliability of the blood test results.

Expert Testimony

Expert witnesses, such as toxicologists or forensic specialists, can testify about the limitations and uncertainties of THC blood testing.

Inaccurate Testing Equipment

The accuracy and reliability of the testing equipment used to analyze the blood sample can be called into question. This may include challenging the calibration, maintenance, or proper functioning of the testing device.

Chain of Custody Issues

A DUI defense attorney in Breckenridge may investigate whether there were any gaps in the chain of custody of the blood sample. If there are doubts about the sample’s proper handling, storage, or transportation, it could raise concerns about the integrity of the test results.

It is important to note that the effectiveness of these defenses may vary depending on the specific circumstances of the case. An experienced lawyer will tailor the defense strategy unique to your situation to maximize the chances of a favorable outcome.

Contact an attorney today for a free legal consultation.