By Attorney Charles E. Liken Jr., former Colorado Deputy District Attorney. Legal to use doesn't mean immune to charge — and the science of drug impairment is far shakier than the science of alcohol. That cuts both ways, and good defense uses it.
Charles E. Liken Jr., Esq. — On the Legal Front Lines · Former Government Investigator, Denver Human Services · Licensed Colorado Attorney · 20+ Years in Private Practice · Former Colorado Deputy District Attorney · Colorado Court-Appointed Child and Family Investigator
There's no separate “DUID” statute — it's the same DUI/DWAI law (§ 42-4-1301, C.R.S.) applied to drugs, with one marijuana-specific rule and a very different evidentiary landscape.
At 5 ng/mL or more of delta-9 THC in whole blood, jurors may infer DUI (§ 42-4-1301(6)(a)(IV), C.R.S.) — but the inference is permissible, not conclusive, and regular users carry residual THC long after impairment ends.
Where LLF comes in: We try these numbers with the science: THC pharmacology, tolerance, and timing make 5 ng a genuinely contestable line — unlike 0.08.
Colorado legalized possession and use; it never legalized impaired driving. The state's burden remains actual impairment at the time of driving — dispensary receipts prove purchase, not impairment.
Where LLF comes in: The defense isn't “it's legal” — it's “prove impairment.” We hold the state to that burden with the rigor of someone who used to carry it.
Ambien, benzodiazepines, opioids, even when properly prescribed and taken, driving while impaired by them can be charged. The prescription matters to the story; it isn't a shield.
Where LLF comes in: Dosing schedules, prescriber testimony, and pharmacology often separate therapeutic levels from impairment — details that get investigated, not assumed.
Drug Recognition Evaluators follow a 12-step protocol and testify like clinicians — but their conclusions are opinions from a checklist, with error rates cross-examination can expose.
Where LLF comes in: DRE opinions get tested the way prosecutors prepare them — against the protocol manual, step by deviated step.
Under § 42-4-1301.1(2)(b), C.R.S., when drug impairment is suspected and the officer has probable cause, you may be required to submit to blood, saliva and urine testing where that is reasonable. Everything from draw technique to lab quantitation limits is discoverable and challengeable — and drug quantitation is harder science than alcohol.
Where LLF comes in: Lab accreditation records, analyst proficiency, and quantitation uncertainty: the investigator's checklist, applied to their lab.
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There's no true 'limit' — 5 ng/mL of THC in blood permits (but does not require) an inference of DUI under § 42-4-1301(6)(a)(IV), C.R.S. Impairment remains the question, and the inference is rebuttable.
Yes. Lawful prescription is not a defense to driving while actually impaired — though proper therapeutic use is often powerful evidence against impairment.
Express consent applies: under § 42-4-1301.1(2)(b), C.R.S., when drug impairment is suspected and the officer has probable cause, you may be required to submit to blood, saliva and urine testing where that is reasonable, and refusal carries the same license consequences as an alcohol refusal.
DRE conclusions are structured opinions, not laboratory science — protocol deviations and known error rates make them among the most cross-examinable evidence in a DUID case.
Alcohol has a century of dose-response research behind 0.08. Drugs don't: blood levels correlate poorly with impairment across users, tolerances, and time. Prosecutors know these cases are harder — as a former Deputy District Attorney, Attorney Liken weighed that difficulty in his charging decisions, and he weighs it in your defense now.
That's why DUID files lean so heavily on officer observations and DRE opinions — the most subjective, most cross-examinable evidence in the building.
Registry status doesn't change the 5 ng inference — but chronic-use pharmacology powerfully undercuts it. If you're a patient facing a DUID, the science of your own use pattern may be your best witness.
Before you talk to anyone — DA, DMV, insurance — get twenty minutes with the prosecutor turned defender. Don't let the DMV hearing-request deadline, generally seven days from your notice of revocation, pass.
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