Hearing sirens and seeing red and blue flashing lights in your rear-view mirror is a situation no one in California wants to be in. If a person is being accused of driving under the influence of alcohol, they may expect that they will be asked to perform some standard field sobriety tests and that they will be asked to submit to a breath test to determine whether their blood alcohol content level is above the legal limit. However, the police's ability to test whether a person is driving under the influence of drugs is more of a gray area.
Police officers may be able to smell drugs such as marijuana on a person or in the person's vehicle. However, actually proving in court that the person was driving under the influence of drugs is not as easy as proving the person was driving under the influence of alcohol. This is because, unlike standardized field sobriety tests and instruments such as Breathalyzers, there is no real scientific method to determine if a person is driving under the influence of drugs.
Let's look at marijuana, for example. This drug can remain in a driver's body for weeks, and have no effect on the person's ability to go about their daily life, including driving. This makes it difficult for prosecutors to prove that the person was driving while impaired.
In the end, however, a DUI/DWI charge based on drugs is still within the realm of possibilities, no matter how slight. Those who are accused of such crimes may benefit from seeking legal help. An attorney can craft a solid argument in the accused's favor, so that a fair and appropriate outcome can be reached.
Source: CBS Sacramento, "Science Lagging When It Comes To Determining Marijuana DUI," Drew Bollea, May 3, 2017