How Can Police Tell A Person Is Under the Influence?

Police use several tactics to tell if a person is driving under the influence. With alcohol; intoxication is usually pretty obvious but what about other drugs?

Minnesota DWI laws dictate that it is illegal to drive while under the influence of alcohol, scheduled drugs and hazardous chemicals. Police use field sobriety tests, breathalyzers and chemical tests for drugs but detection can be tricky and inaccurate.

Visual Evidence

An officer will primarily try to smell alcohol or drugs such as marijuana or methamphetamine. Another clue is bloodshot eyes for alcohol and marijuana and dilated pupils for opiates and heroin. Certain other drugs such as dextromethorphan and inhalants will cause the pupils to enlarge.

Slurred speech is a dead giveaway along with confusion and poor memory.

The Field Sobriety Test

Police forces a crossed America pretty much all use the same standardized field sobriety test. The test is composed of three components. The first (and pretty much impossible to cheat) is the horizontal gaze nystagmus. This is when the officer shines the light in a suspect’s eyes and asks them to follow the officer’s finger to each side of their peripheral vision without turning their head. If the person is drunk or high on certain drugs then the eyes will twitch a bit on each peripheral.

The next is the walk and turn and the third is to stand on one leg.

While some forces have additional testing (such as saying the alphabet backwards) generally these three tests will be enough to tell if a breathalyzer, urine or blood test is in order.

The unfortunate fact is that field sobriety tests can be highly inconsistent and even inaccurate.

The Breathalyzer

Minnesota and most of the United States have laws that it is illegal to drive with a blood alcohol content of .08 or more. If an officer suspects a driver to be drunk; then a breathalyzer will be administered. There are two types of breathalyzers. The first is a handheld field breathalyzer. This type has been found to not be quite as accurate as the second type of breathalyzer. The second type is a very large machine at the station. This machine is considered to be very accurate and is tested and calibrated regularly to ensure the highest accuracy.

Field Drug Tests

Police officers also use drug test kits that are commonly referred to as NIK tests. The narcotics identification kits use wet chemistry to test for a variety of drugs such as cocaine, methamphetamine, marijuana, LSD, PCP, heroin, opiates and more. NIK tests are controversial because they are so cheaply purchased and considered by some to be inaccurate and of poor quality.

The Marijuana Issue

Aside from the fact that states are pushing for the legalization of marijuana; the drug is impossible to have a “legal limit” on.  THC levels when marijuana is smoked will spike quickly and drop rapidly; often base lining only two hours after smoking. Since police officers cannot really give a urine or blood test on the field; they are forced to rely on the standardized field sobriety test. To further complicate matters; Minnesota DWI law dictates a clear exception for being high on marijuana.

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