If you were charged after a traffic stop and you had not used marijuana that day, a Virginia marijuana DUI lawyer hears the same frustrated question all the time: how can this be a DUI if I smoked days ago and was sober behind the wheel? The answer comes down to a gap between what a test detects and what the law actually has to prove, and that gap is often the heart of the defense.
It is possible to be charged, yes. THC and its byproducts can stay in your body long after the high is gone, so a blood test taken after a stop can come back positive even when you were not impaired at all. But a charge is not a conviction. To convict you of a marijuana DUI in Virginia, the state has to prove you were actually impaired while driving, not just that cannabis was somewhere in your system.
Longer than most people expect, and this is exactly why “I smoked days ago” cases happen.
Federal safety regulators acknowledge this problem directly. The National Highway Traffic Safety Administration has stated that, unlike alcohol, there is no reliable link between a specific THC blood level and driver impairment. That distinction, presence versus impairment, is the single most important idea in these cases.
With alcohol, 0.08 is a bright line. Marijuana has no equivalent in Virginia. Possessing marijuana is legal for adults 21 and older under Va. Code § 4.1-1100, but impaired driving is still a crime under Va. Code § 18.2-266. That statute sets no per se THC level. Instead, it requires the government to show your ability to drive safely was actually affected. There is no number the prosecution can point to and no number you can rely on as “safe.”
Because there is no per se limit and because a test only shows presence, the government has to build a marijuana DUI out of subjective evidence: driving behavior, an officer’s observations, field sobriety tests designed for alcohol, and a drug recognition evaluation that is ultimately an opinion. Each of those can be challenged. So can the timing of a blood draw and what a positive result really proves. A prosecutor who cannot connect a test result to impairment at the time of driving has a weak case, which is why “I smoked days ago” facts often lead to a dismissal or a reduction. No lawyer can promise a result, and every case turns on its own facts, but this is fertile ground for a defense.
If you were sober when you drove but tested positive for THC, do not assume the case is airtight against you. It usually is not. The sooner a lawyer reviews the stop, the testing, and the timeline, the more room there is to attack the impairment question. Our team defends drivers throughout Fairfax, Arlington, Alexandria, and the surrounding Northern Virginia courts.
Can I be charged with a DUI if I smoked yesterday and felt fine?
You can be charged, but you should not be convicted if you were not impaired while driving. THC lingers in the body, so a test taken after a stop can be positive even though the effects were long gone. The law still requires proof of impairment at the time you were driving, not just the presence of cannabis. That gap is exactly what a defense attorney attacks, and it is why day-after cases are often winnable.
How long does THC show up in a blood test?
It varies widely. For an occasional user, active THC in blood often fades within hours, while frequent or heavy users can test positive much longer. Metabolites can persist even after the active compound is gone. Because there is so much individual variation, and because none of these tests measures impairment, a positive blood result days after use says little about whether you were actually high behind the wheel.
Is there a legal THC limit for driving in Virginia?
No. Unlike the 0.08 alcohol limit, Virginia sets no THC blood concentration that automatically establishes guilt. Marijuana DUIs are prosecuted under an impairment standard, meaning the state must prove your driving was actually affected. This makes these cases harder for prosecutors than a typical alcohol case built on a breath number, and it is a major reason marijuana DUIs are challenged.
Does having a medical cannabis card protect me from a DUI?
No. A medical cannabis authorization lets you use cannabis legally, but it does not give you permission to drive while impaired. If the state can prove your ability to drive safely was affected, you can still be charged and convicted regardless of a card. The card does not change the impairment analysis, though it may be relevant context an attorney can address as part of your defense.
This article is general legal information about Virginia law, not legal advice, and it does not create an attorney-client relationship. Every case depends on its specific facts. For advice about your situation, speak with a licensed Virginia attorney.