What it Means to be “Under the Influence”
In most states, being “under the influence” means that the driver is incapable of driving safely due to the effects of drug or alcohol use.
As we know, when it comes to alcohol, a blood alcohol level of 0.08 percent of the driver’s blood, by volume, will conclusively establish that the driver is under the influence (if the level is less, the prosecutor can still point to the driver’s actions to prove that he was under the influence). In some states, the blood alcohol level threshold is even lower if the driver is a minor. Wow, this is new news with Cannabis driving!
When marijuana is involved, however, states have different approaches to establishing that the driver was under the influence, as shown below.
Per se laws
In states with so-called “per se” DUI laws, any amount of marijuana in the driver’s system at the time of the offense will conclusively establish impairment. In these states, a prosecutor will not need to present any further evidence (such as behavior consistent with being under the influence or unsafe driving) in order to establish that the driver was under the influence. But is being under the influence the same with pot as it is with alcohol?
State per se laws often include marijuana metabolites—compounds left over when the body metabolizes (or processes) marijuana—which can remain in a person’s body for days, weeks, or longer after marijuana use. While metabolites indicate that the person ingested marijuana at some point in the past, they do not indicate how long ago, or necessarily point to current impairment. Even so, state per se laws that include metabolites accept their presence as conclusive evidence of impairment for the purposes of a DUI charge.