||You are considered to be under the influence if your ability to drive is "substantially Impaired." It makes no difference if the drugs are legal or illegal.
DUI Drugs, DUID, or Driving Under the Influence of Drugs
In Colorado, it is illegal to drive if you meet the legal definition of being "under the influence" of drugs. Under the law, you are considered to be under the influence if your ability to drive is "substantially impaired." It makes no difference whether the drugs causing this effect are illegal drugs, or lawfully obtained prescription drugs. A conviction for the driving under the influence of drugs will lead to the same penalties as driving under the influence of alcohol.
DUI cases that are based on drugs are often good defense cases. The DUI Per Se statute cannot be used by the prosecutor, since that law only prohibits an alcohol level, not a drug level, in a person's blood. This means that the District Attorney must use other evidence to prove that your driving ability was substantially impaired — usually the officer's testimony about your appearance and demeanor; and mistakes you made while on the road.
DUID cases usually involve urine or blood test results that show some level of drug content in your blood. However, the District Attorney may have trouble proving you guilty because no specific blood content legally establishes guilt. Unlike alcohol cases, there is no number like 0.08 that objectively measures impairment from drugs.
If you take a drug-related DUI case to trial, we will likely recommend the use of a toxicologist as an expert witness. This expert would explain to the jury that a specific blood level of a drug does not correspond with impairment, and that each individual's tolerance to a drug varies greatly. Further, the drug may be detected in your blood as a result of drug use long before the date on which you were driving, and therefore may have had no effect on your ability to drive.
If the officer that arrested you was not a certified "Drug Recognition Expert," your lawyer can try to prohibit him from testifying to his observations about your level of drug impairment. At the least, the officer's lack of specific training will diminish the credibility of his testimony. In cases where no drugs were located in your car, the officer's unqualified and uncertified opinion may not be enough to prove you guilty.
A DUI charge can also be based on a combination of both alcohol and drugs. In such a case, the prosecutor would not have to show a specific blood level of either alcohol or drugs - but only that your ability to drive was substantially impaired by the combination of both.