Not necessarily; it depends on the circumstances. Consider a case in Jacksonville, Florida where a driver caused a serious motor vehicle accident. The Jacksonville police officer showed up and reported that this driver appeared impaired, unresponsive and subject to mood swings. At the hospital, a blood sample was taken from the driver, and the test results were positive for marijuana metabolites. Can the results of this blood test be used against that driver in a trial for driving under the influence of a controlled substance (also referred to as DUI or DWI)?
In this case, a criminal defense lawyer would argue that the existence of marijuana metabolites (as opposed to the actual parent drug) in a defendant’s blood sample does not prove that the driver was under the influence of marijuana or otherwise impaired at the time of the accident. Forensic toxicologists would be used to testify that marijuana metabolites can remain in a person’s system for days after marijuana use and far beyond the time when the effects of marijuana use have worn off. The issue at the DUI trial is whether the defendant driver was under the influence of marijuana at the time of the crash to the extent that his normal faculties were impaired. Since any marijuana use could have occurred days before the crash, this evidence of marijuana metabolites is marginally relevant to the criminal case, if at all. On the other hand, this evidence of marijuana metabolites in the defendant driver’s system is highly prejudicial as it may lead jurors to assume the defendant was impaired or paint him as a drug user who was likely impaired or prone to commit such crimes. Because of the danger of this kind of unfair prejudice at the defendant’s trial, the criminal defense lawyer should argue that this evidence should be excluded from the criminal trial as more prejudicial than useful to prove the elements of the DUI crime.