The State’s easiest argument in a drug case is also its weakest: that a given level means a given amount of impairment for everyone. Pharmacology does not work that way. People build tolerance, and a level that would impair a first-time user can have little or no effect on someone who takes the same substance regularly. The individual matters, and a number that ignores the individual does not prove much.
The same drug level lands in two different places. For a first-time user it can mean real impairment, while for a tolerant patient on a stable dose it may mean almost none. A number alone cannot tell the two apart.
How Tolerance Changes the Picture
Tolerance is the body’s adjustment to repeated exposure. With many medications and substances, the same dose produces a smaller effect over time, so the relationship between level and impairment shifts with the person. A patient who has taken a medication daily for months can function normally at a level that would noticeably affect a first-time user. Forensic and medical references treat this as a basic feature of how drugs work, not as an exception.
Why an Average Does Not Decide Your Case
Prosecutors often reach for what a drug does to people in general. That is a statement about a population, and you are an individual. The law asks whether your normal faculties were impaired, which depends on your tolerance and your history, not on an average drawn from people who are not you. Treating a level as a fixed quantity of impairment skips the very question the State has to answer.
The government could not find a number that fits everyone
The research found this when it went looking, so it is more than a lawyer’s argument about averages. When scientists working with NHTSA studied hundreds of drivers, they could not find a blood level that reliably marked impairment, and they concluded there is no evidence that any objective threshold establishes impairment across people. The reason is tolerance. Someone who takes a medication every day, or uses cannabis regularly, adapts to it, so a level that would floor a first-time user leaves them able to function. A number treats every body as the same body, and yours is your own, with your history and your chemistry. Florida law understands this, because it asks whether your normal faculties were impaired, which is a question about you and not about a statistic.
Putting the Individual Back in the Case
My job is to replace the one-size assumption with the real person. That means your history with the substance or medication, the reported level read against what it means for a tolerant user, and the officer’s actual observations of your driving and performance. Where the State has assumed impairment from a number, tolerance is often the reason that assumption does not hold.
Why a Population Average Is Not You
The State’s expert often testifies about what a drug does to people in general, drawing on studies of subjects who were given a dose under controlled conditions. Those studies are useful, but they describe a group, and many of the subjects were not regular users. Functional tolerance means a person who takes a substance regularly adapts to it, so the same level produces less effect than it would in the volunteers from a study. When an expert carries a group average straight onto your client, the cross-examination is straightforward: the studies did not include this patient, did not account for months of daily use, and cannot say what this level meant for this person. The law asks about your normal faculties, which is an individual question, and a population average cannot answer it. The goal is to move the court away from a chart of what a drug does on average and toward the real person, with a real history, who was driving that night.
The State likes numbers because a number feels like certainty, and it hides how different people really are. I put you back into your own case, your tolerance, your medications, your health, and the way you looked and moved that night, and I show the jury that a level pulled from a population study says nothing reliable about the person in front of them. I know the science of tolerance and individual variation, so I do not let an average stand in for you when your freedom is the thing on the line.
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 Tolerance
What is drug tolerance?
Tolerance is the body's adjustment to repeated exposure to a drug. Over time, the same dose produces less effect, so a level that would impair a first-time user may have little or no effect on a regular user. Tolerance is well documented for many medications and substances, and it is one reason a drug level cannot be read as a fixed amount of impairment.
Why does tolerance matter in a DUI case?
Because the State often treats a drug level as if it means the same thing for everyone. It does not. A patient who takes a medication daily can be tolerant to its sedating effects and drive normally at a level that would affect someone taking it for the first time. Without accounting for the individual, a number says very little about impairment.
Does tolerance always help the defense?
Usually it cuts against the State's shortcut of equating a level with impairment, but the facts decide each case. A recent dose increase or a first use can have a stronger effect before the body adjusts. I look at the individual history, not a population average.
Can the State just use an average effect?
It often tries to, by citing what a drug does to people in general. The problem is that you are not an average. The relevant question is what the drug did to you, given your history and tolerance, and a general statement about a population does not answer that.
How do you show tolerance in a case?
Through your history with the substance or medication, the reported level against what that level means for a tolerant person, and the actual observations of your driving and performance. The point is to replace a one-size assumption with the real individual in front of the court.
I use my medication daily, so does the level even mean anything?
Often much less than the State suggests. Tolerance means a regular user can function normally at a level that would impair a first-time user, and researchers working with NHTSA found no blood level that reliably marks impairment across people. Florida law asks whether your normal faculties were impaired, which is a question about you, not an average.
Related pages: Presence is not impairment, prescription and therapeutic drug DUI, why there is no per se drug limit, 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.
