In most states a police officer must prove that a motorist is impaired (through field sobriety tests) before they can charge them with a DUID (driving under the influence of drugs) for marijuana.
However, some states, such as Washington, have a per se limit for THC. This means if you have a specific amount of THC in your system (5ng/ml in Washington), you’re automatically guilty of a DUID, regardless of actual impairment.
Thankfully, Oregon’s Liquor Control Commission – the entity tasked with overseeing the newly legal marijuana industry – has recommended against a per se THC limit in Oregon. The recommendations were made as part of the commission’s DUI Legislative Report released last month.