The legality of marijuana use differs greatly between states. Some states allow its recreational use, some allow its medical use, and other states prohibit marijuana use altogether. But in every state, it's still illegal to operate a motor vehicle while under the influence of marijuana or any other substance. This article explains some of the common DUI laws related to marijuana, when a driver can be convicted of DUI for marijuana use, and the possible penalties for marijuana-related DUI conviction.
Depending on what state you live in, impaired driving might be called "driving under the influence" (DUI), "driving while impaired" (DWI), or some similar name. While states use different names for the offense, the aim of these laws is the same: to protect public safety by keeping impaired drivers off the roadways.
To get a DUI conviction in court, prosecutors must have sufficient evidence to prove the driver was, in fact, impaired. In every state, prosecutors can prove a marijuana DUI charge by showing the driver was actually impaired by marijuana use. And, in some states, prosecutors can establish the charge by proving the driver has a certain concentration of THC (the main psychoactive component in marijuana) in his or her system.
Each state has slightly different definitions for what constitutes sufficient impairment to be in violation of DUI laws. Generally, a driver is considered to be under the influence (and in violation of the law) when the consumed substance has substantially deprived the driver of normal control or clarity of mind so that the driver is incapable of safely driving.
To prove impairment, the prosecutor typically relies on the testimony of the arresting officers. For example, the officer might testify that the driver had bloodshot eyes, performed poorly on field sobriety tests, and appeared confused and disoriented. The prosecutor can also use chemical test results (if available) along with expert testimony to show how marijuana can affect and impair a person's ability to drive.
All states have per se DUI laws that prohibit driving with a blood alcohol concentration of .08% or more (.05% or more in Utah). And some states have similar per se laws that apply to marijuana use. For example, having 2 nanograms of marijuana per liter of blood in Nevada is considered per se impaired driving. Similarly, in Utah, a driver with any measurable amount of marijuana metabolite (such as THC) can be convicted of a per se DUI.
Implied consent laws generally require drivers lawfully arrested for a DUI to submit to a chemical test of the driver's blood or urine. The results of these tests show what substances the driver has consumed and the concentration of the consumed drugs. Prosecutors can use these test results to prove a per se DUI charge in court.
In states with medical marijuana, many users will possess a valid prescription authorizing their possession and usage of marijuana. But a medical marijuana prescription doesn't authorize a driver to operate a vehicle while impaired. In other words, the fact that a driver had a valid prescription for marijuana generally isn't a legal defense to a DUI charge.
However, in some states, a medical marijuana prescription can provide a defense for a per se DUI charge where the driver had a THC concentration over the legal limit. (But note, this defense doesn't apply to a DUI charge based on driver impairment.)
The penalties for driving under the influence of marijuana are generally identical to driving under the influence of alcohol or other drugs. The penalty ranges are set out by statute, but judges often have sizeable discretion in sentencing. The possible penalties (the ranges) for a DUI conviction are increasingly more severe for each subsequent offense. In other words, the penalties for a second offense are more severe than those for a first offense, the penalties for a third offense are more severe than those for a second offense, and so on.
Every state has different DUI penalties, but here is some general information about the penalties a driver might face for a marijuana DUI conviction:
The penalties a driver faces for a marijuana DUI conviction will typically be more severe if certain aggravating factors are present. Aggravating factors might include things like having a minor passenger and causing an injury or death.