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Proving impairment in drugged driving cases

On Behalf of | Dec 21, 2020 | Blog, Criminal Defense

When prosecutors in Michigan and around the country seek to prove intoxication in drunk driving cases, they usually introduce the results of breath or blood tests that show the defendant was behind the wheel with a blood alcohol concentration of .08 or higher. The science linking BACs to impairment is well established, and even individuals who consume large amounts of alcohol on a daily basis are unable to operate a vehicle safely when they are over the legal limit. However, the same cannot be necessarily said of prescription or recreational drugs.

THC evidence unreliable

While the effects of alcohol consumption are highly predictable regardless of an individual’s drinking habits, people react to drugs in different ways. This is especially true of substances that users develop a tolerance for over time like marijuana. In 2018, Michigan Gov. Rick Snyder set up a panel to assess the scientific link between THC levels in the blood and impairment. The panel included toxicology scientists, pharmacists and law enforcement experts. The Impaired Driving Safety Commission reported its findings in March 2019. They concluded that THC evidence is unreliable and likely leads to unimpaired individuals being charged with DUI.

Subjective evidence

With no credible scientific evidence to turn to, prosecutors may be forced to rely on the testimony of police officers and the results of field sobriety tests to prove impairment in drugged driving cases. This type of evidence is highly subjective, and it may be of little practical use. Field sobriety tests were designed to identify alcohol intoxication, but drugs affect the mind in different ways. This is why the U.S. Institute on Drug Abuse says that a reliable roadside test for drug impairment does not yet exist.

Beyond reasonable doubt

Prosecutors must prove guilt beyond a reasonable doubt in DUI cases, which could be extremely difficult for them given the current tools available to law enforcement. If you are charged with driving while under the influence of drugs, an experienced criminal defense attorney could cite reports such as the one written by the Impaired Driving Safety Commission to challenge the validity of toxicology evidence and support a motion to dismiss.