A DWI for intoxication by drugs is ultimately about impairment, and Missouri has no THC number to measure it.
Missouri’s DWI law covers driving under the influence of alcohol, a controlled substance, a drug, or any combination. Marijuana, prescription medication, an illegal drug, or a mix of alcohol and drugs can all become a DWI if impairment is alleged.
Unlike alcohol, there is no set number for drugs, no equivalent of the .08 limit, so a drug DWI turns on whether the State can prove you were actually impaired while driving. Michael Boyd reviews the stop, the observations, the testing, and the medical side himself. If you were arrested in the St. Peters, St. Charles, O’Fallon, or Wentzville area, call 636-229-4999 to talk directly with him.
What Is a Drug DWI in Missouri?
A drug DWI is a Missouri DWI where the alleged impairment comes from a drug, a controlled substance, marijuana, or a combination, instead of or along with alcohol. It is charged under the same statute as an alcohol DWI, and it does not require any alcohol at all.
What makes it different is the proof. An alcohol case often centers on a breath or blood number. A drug case has no equivalent number to point to, so it is built from other evidence: how you were driving, what the officer observed, field sobriety and drug-recognition evaluations, and blood or urine testing. The central question is whether all of that actually shows impairment at the time you were driving.
| Issue | Alcohol DWI | Drug DWI |
|---|---|---|
| Is there a set limit? | Yes: .08 percent (lower for CDL and under 21) | No. Missouri sets no per se limit for THC or other drugs |
| Common evidence | Breath or blood alcohol result | Officer observations, field sobriety tests, drug-recognition evaluation, blood or urine results |
| Main proof issue | Whether the alcohol result supports intoxication | Whether the evidence shows actual impairment while driving |
| Does a positive test settle it? | A number at or over .08 is strong evidence on its own | No. The presence of marijuana or drugs can remain in your system well after its effects end, so presence alone is not impairment |
Can You Get a DWI for Marijuana in Missouri?
Yes. Marijuana is legal to buy and possess for adults in Missouri, but driving while impaired by it is not. Amendment 3 legalized adult use. It did not legalize impaired driving, and the same DWI statute applies whether or not the marijuana was bought lawfully.
Here is the part that matters most for these cases: Missouri has no legal THC limit. There is no marijuana equivalent of the .08 alcohol number. A marijuana DWI has to be proven through impairment, not through a test reading alone. Amendment 3 itself makes this point, stating that the mere presence of THC in your system does not by itself show you were intoxicated.
That distinction is central, because THC can stay detectable in blood or urine for days or even weeks after use, long after any effect has worn off. A regular user can test positive while completely sober. So a positive result raises a timing question, not an automatic answer: does the evidence show you were impaired when you were driving, or only that you used marijuana at some point?
A medical marijuana card does not change this. It may explain why marijuana was present, but it does not permit impaired driving, and it does not end the case.
Can Prescription or Over-the-Counter Medication Lead to a DWI?
Yes. Many people charged with a drug DWI were not using anything illegal. They took medication for sleep, pain, anxiety, attention, or allergies, sometimes exactly as prescribed. A lawful prescription is a defense to a possession charge, but it is not, by itself, a defense to a DWI if the State claims the medication impaired your driving.
These cases call for a different kind of review: the medication, the dosage, the timing, the warnings, your medical history, and whether the evidence actually ties the medication to impaired driving rather than simply showing it was in your system.
What the State Has to Prove, and How
A drug DWI is not proven just because a substance shows up in a report. The State still has to prove two things: that you operated the vehicle, and that you were under the influence of a drug, alcohol, or a combination while doing it.
Because there is no number to rely on, that proof is usually assembled from several pieces: the reason for the stop, your driving, the officer’s observations, field sobriety tests, any statements, and blood or urine results. In many drug cases the State also relies on a Drug Recognition Expert, an officer trained in a standardized twelve-step evaluation meant to identify drug impairment and rule out medical causes. That evaluation can be persuasive, but it is subjective and open to challenge, and many Missouri police agencies do not have a certified DRE, so some drug cases are handled by officers with limited drug training.
Marijuana cases have added a newer wrinkle. Since legalization, courts are still working through questions like whether the smell of marijuana alone can justify a stop or a search. Each piece of the State’s case has to be checked against the rest of the record.
What Michael Boyd reviews in a drug DWI case
Drug cases often come down to whether the pieces actually line up. Each of these gets checked before the accusation is treated as proven.
Reason for the stop
Whether the officer had a lawful basis to stop the vehicle in the first place.
Driving behavior
Whether the driving actually showed impairment, or whether there is another explanation.
Officer and DRE observations
Whether the report, the drug-recognition evaluation, and the video hold up to scrutiny.
Field sobriety tests
Whether tests built around alcohol were the right tool, and whether they were done correctly.
Blood or urine evidence
Whether the sample, timing, chain of custody, and interpretation actually point to impairment.
Medication and medical history
Whether a prescription, dosage, or medical condition explains the evidence differently.
Blood and Urine Tests in Drug DWI Cases
Blood and urine testing can be important evidence, but a positive result is not the end of the analysis. A drug result has to be connected to impairment at the time of driving, and with drugs that connection is rarely simple.
The review looks at when the sample was taken, what was actually collected and measured, whether it was handled and stored correctly, and whether the result fits the officer’s observations and the video. A lab result can confirm that a substance was present while leaving the real question, impairment while driving, unanswered.
If the officer requested a chemical test and you refused, the case also has a separate refusal issue, with its own license consequences and deadline to act.
Penalties and License After a Drug DWI
At the same offense level, a drug DWI is generally penalized like an alcohol DWI. A first drug DWI is usually handled at the first-offense level, and a repeat drug DWI raises the same enhancement questions as any other DWI.
The license side has a few drug-specific wrinkles. A drug DWI conviction can bring a license suspension like an alcohol case. Refusing a requested drug or alcohol test can trigger a separate one-year revocation. And Missouri’s “abuse and lose” law allows a court to revoke an adult’s driving privilege for a year for using drugs while driving. The deadlines, the revocation process, and reinstatement follow the same rules as any Missouri license case. The practical point holds here too: do not assume the license issue can wait for the criminal case.
If the Driver Is Under 21 or Holds a CDL
A drug DWI can carry extra consequences depending on who is driving. An under-21 driver faces a lower threshold and the zero-tolerance license rules that apply under 21. A commercial license carries its own disqualification rules and job consequences for CDL holders. This page stays focused on the drug-impairment proof itself.
How Michael Boyd Helps With a Drug DWI
Drug DWI cases typically warrant careful review by a DWI lawyer who understands this specific area of law because the evidence is usually less direct than an alcohol number. Michael Boyd reviews the stop, the field sobriety and any DRE evaluation, the officer’s observations, the blood or urine evidence, your medication history, the lab work, and the video.
You work directly with him. He handles the review and the court work himself, including the questions that decide these cases: whether the stop was lawful, whether the evidence actually shows impairment, whether a test result is being read for more than it proves, and whether the license issue needs action now.
Find your paperwork, including anything about medications you take, and call 636-229-4999 to talk it through.
What is a drug DWI in Missouri?
A drug DWI is a DWI where the State claims you were under the influence of a drug, controlled substance, marijuana, prescription medication, or a combination while operating a vehicle. It is charged under the same statute as an alcohol DWI and does not require any alcohol.
Can I get a DWI for marijuana in Missouri?
Yes. Marijuana is legal to possess for adults, but driving while impaired by it is not. A marijuana DWI depends on whether the State can prove impairment while you were operating the vehicle.
Is there a legal THC limit in Missouri like the .08 alcohol limit?
No. Missouri sets no per se THC limit. A marijuana DWI has to be proven through impairment, and the presence of THC alone does not establish that you were intoxicated.
Can prescription medication cause a DWI charge?
Yes. A prescription can be lawful to possess and still be part of a DWI if the State claims the medication impaired your driving. A lawful prescription is not, by itself, a defense to impairment.
Can a blood or urine test prove a drug DWI?
It is evidence, but it has to be tied to impairment at the time of driving. Drugs like THC can stay detectable long after their effects end, so timing, handling, and interpretation all matter.
What is a Drug Recognition Expert?
A DRE is an officer trained in a standardized twelve-step evaluation used to identify drug impairment and rule out medical causes. The findings are subjective and can be challenged, and many Missouri agencies do not have a certified DRE.
What if I had a medical marijuana card?
The recreational use of marijuana has been legalized by the State of Missouri so a medical marijuana card is no longer needed in order to lawfully possess marijuana. That said, a medical card may explain lawful use, but it does not allow impaired driving. The question in court is still whether the State can prove impairment while you were operating the vehicle. The same is true for all cases where it is alleged that the driver was intoxicated as a result of marijuana consumption.
What if I refused a drug test?
Refusing a chemical test in Missouri, whether for alcohol or drugs, can trigger a separate one-year chemical revocation with its own license process and deadline.
Will a drug DWI affect my license?
Yes, it can. A conviction can bring a suspension, a refusal can bring a one-year revocation, and Missouri’s “abuse and lose” law allows a one-year revocation for drug-related driving. The exact result depends on the facts.
Do I need a lawyer for a drug DWI?
These cases turn on technical proof: the stop, field sobriety and DRE evaluations, testing, timing, and whether the evidence actually shows impairment. Early review can change how the case is defended.
A drug DWI turns on impairment, not just a positive test.
A test result, a medication, or a marijuana allegation does not answer the real question by itself. Michael Boyd can review the stop, the observations, the testing, and the timing, and explain what the State still has to prove.
Every case is different. If you were arrested for DWI for intoxication by marijuana or drugs, Michael Boyd can explain your rights and the potential consequences of your arrest. Consultations are free.