One feature of Florida law shapes every drug DUI: there is no per se limit for any drug. With alcohol, the law fixes a line at 0.08, and a blood or breath result at or above it can carry the case on the number alone. No equivalent number exists for marijuana, prescription medication, or any controlled substance. That single fact changes how a drug case has to be tried.
Because there is no number to lean on, the prosecution has to fall back on the impairment theory, and that is a much heavier lift than flashing a lab report to a jury.
With alcohol the law draws a line at 0.08 and the number can carry the case. With drugs there is no line, so the prosecution has to prove that your faculties were impaired.
Where the Per Se Rule Lives
Florida Statute 316.193 sets out two ways to prove a DUI. One is the impairment theory, where the State shows your normal faculties were affected by alcohol, by a chemical substance under section 877.111, or by a controlled substance under chapter 893. The other is the per se theory, where a blood or breath alcohol level of 0.08 or higher is enough by itself. The per se theory is written in terms of alcohol concentration, and it does not reach drugs. So when the case involves a drug, the State is left with the impairment theory and has to prove a real effect on your driving.
What the statute really says, and what it leaves out
Florida’s DUI law, section 316.193(1)(a), makes it a crime to drive under the influence of a controlled substance to the extent that your normal faculties are impaired. The number everyone knows, 0.08, lives in the very next lines of the same statute, and it applies to alcohol only. There is no equivalent number for drugs, no THC level, no cutoff, nothing. That gap is deliberate, a recognition that drug levels do not map onto impairment the way alcohol does. Florida courts have held the line on it, too. In West v. State, 553 So. 2d 254 (Fla. 4th DCA 1989), an appeals court found it was reversible error to put a mere trace of a drug in front of the jury, because a trace is not proof that anyone was impaired.
What Impairment of Normal Faculties Means
Florida’s standard jury instruction describes normal faculties as the ordinary abilities of daily life, including the ability to see, hear, walk, talk, judge distances, drive, make judgments, and act in emergencies. Proving that a drug damaged those abilities is very different from proving that a drug was present. People function normally with all sorts of substances in their blood, from prescribed medication to the residue of use days earlier, and the law recognizes that presence and impairment are not the same thing.
Why This Helps the Defense
The absence of a per se limit removes the prosecution’s easiest path. It has to connect a specific drug to a specific deficit in your driving, at the specific time you were behind the wheel, and it usually has to do so through an officer’s opinion and a lab result that only shows exposure. Each of those links can be tested. The drug may be an inactive metabolite that shows past use, the level may sit in a range that does not impair a tolerant person, and the field evaluation may not support the conclusion the officer reached.
Even the government says a drug number would not work
When lawmakers have floated a per se drug number, the science has not backed them up, and the source saying so is the government’s own. In its 2017 report to Congress, NHTSA stated plainly that per se drug limits are not evidence-based. A Washington State study it relied on found that among thousands of drivers an officer or a drug recognition expert believed were impaired by marijuana, nearly 63 percent already had blood THC below the 5 nanogram line that some states use, simply because the level falls during the hours it takes to draw blood. A follow-up study concluded there is no evidence that any THC threshold reliably marks impairment. So a drug number would sweep in sober people and miss impaired ones at the same time, which is exactly why Florida does not have one.
What the State Uses Instead of a Number
Take away the number and the prosecution has to build impairment out of softer materials, and each one can be questioned. The driving pattern is the first, but speeding, drifting, or a late stop are not specific to drugs and happen to sober drivers every day. The officer’s observations come next, including the look of the eyes, the smell of cannabis, or an admission of use, none of which measures impairment. Then come the field exercises, which were designed and validated for alcohol rather than drugs. In many cases the State turns to a drug recognition evaluation, a twelve-step routine that ends in an officer’s opinion about which category of drug is involved. That opinion is still an opinion, formed by a layperson trained to reach a conclusion, and it carries all the weaknesses covered in the drug recognition pages of this site. None of these is a measurement, and stacking them does not turn presence into proof.
The absence of a magic number is one of the best things your case has going for it, and I lean into it hard. Without a threshold to hide behind, the State has to prove actual impairment with real evidence, the driving, the observations, and the testing, and every one of those is something I can challenge. I make the prosecutor do the work the statute requires instead of pointing at a lab result and calling it a day, because in a Florida drug case the presence of a substance was never the question, your ability to drive was.
I started out as an Assistant Public Defender in Florida’s Thirteenth Judicial Circuit, in Tampa, and today I am one of six ACS-CHAL Forensic Lawyer-Scientists in Florida. I work both the science and the procedure in your case the way the State’s own analysts and officers are trained to, and I show a jury the exact point where the evidence does not hold up. Learn more about my background.
Questions About the Drug Limit
Is there a legal limit for drugs in Florida?
No. The 0.08 per se limit applies only to blood or breath alcohol. Florida has not set a per se level for marijuana, prescription medication, or any other drug. That means a drug case has to be proved under the impairment theory, where the State shows your normal faculties were affected, rather than by pointing to a number.
If there is no limit, how can I be charged at all?
Through the impairment theory in Florida Statute 316.193. The State alleges that a controlled substance under chapter 893 or a chemical substance under section 877.111 impaired your normal faculties while you drove. It does not need a number, but it does need real proof of impairment tied to the drug and to your driving.
Do some states have a per se THC limit?
Yes. A handful of states have set a specific blood THC number, above which a driver is treated as per se impaired. Florida is not one of them, and the science behind those limits is heavily disputed because blood THC does not track impairment the way blood alcohol does.
What are normal faculties?
Florida's standard jury instruction describes them as the ordinary abilities of daily life, including the ability to see, hear, walk, talk, judge distances, drive, make judgments, and act in emergencies. The State has to show a genuine deficit in those abilities caused by the drug.
So the lab result is not the whole case?
Correct. Without a per se limit, the result is just evidence of exposure. It still has to be connected to actual impairment at the time of driving, and that connection is where these cases are contested.
Is there a legal THC limit for driving in Florida?
No. Section 316.193 sets a 0.08 per se limit for alcohol only. For drugs, including THC, there is no number, and the State must prove your normal faculties were impaired. NHTSA itself told Congress that per se drug limits are not evidence-based.
Related pages: Presence is not impairment, parent drug vs metabolite, tolerance and the individual, and drugs and impairment in blood.
This page is general information, not legal advice, and it does not create an attorney-client relationship. Drug DUI in Florida is governed by Fla. Stat. 316.193, section 877.111, and chapter 893, and chemical testing is governed by Fla. Stat. 316.1932 and 316.1933. Procedures and rules change, and every case turns on its own facts. Past results do not guarantee a similar outcome.
