Taking prescribed ADHD medication and driving is not a per se DUI in Montana, because the blood limits for amphetamine and methamphetamine apply only to a person without a valid prescription. The limits are low, though, and a person using a stimulant without a prescription can be over them after one tablet. This page explains how the 2025 limits apply to stimulants. It is part of our Montana DUI Guide.
The Stimulant Entries in Montana's Drug Limits
MCA § 61-8-1002(1)(f), in effect since October 1, 2025, makes it a DUI to drive on the ways of this state open to the public while, "without a valid prescription," a person has a listed substance in their blood at or above a set level. Two entries are stimulants used in medicine.
| Substance | Blood level | On the list? | With a valid prescription |
|---|---|---|---|
| Amphetamine (Adderall, Dexedrine) | 20 ng/mL | Yes, at (1)(f)(i) | Outside the per se offense. Impairment charge still possible. |
| Methamphetamine (prescription form: Desoxyn) | 20 ng/mL | Yes, at (1)(f)(vii) | Outside the per se offense. Impairment charge still possible. |
| Methylphenidate (Ritalin) | None | No | Impairment charge only, with or without a prescription. |
| Caffeine, pseudoephedrine | None | No | Not listed. |
Cocaine and its metabolite are also listed at 20 ng/mL. The complete list is on our page about Montana's drug limits.
Why 20 ng/mL Matters to Patients
The 20 ng/mL figure is not a level reached only by misuse. NHTSA's Drugs and Human Performance Fact Sheets: 2024 describe a study in which a single 12.5 mg oral dose of d-amphetamine produced average plasma concentrations of 21.0 ng/mL at 120 minutes, and a 25 mg dose produced 42.8 ng/mL. Twelve hours after dosing, concentrations were still 15 to 33 ng/mL. The fact sheets describe Adderall as a mixture of amphetamine isomers supplied in tablets from 5 to 30 mg.
One caution on reading those figures: they are plasma concentrations, the statute is written in terms of blood, and NHTSA gives a blood to plasma ratio for amphetamine of 0.6 to 1.0. The two are not identical. The point is only that therapeutic dosing produces levels in the neighborhood of the statutory number.
For methamphetamine, NHTSA states that blood concentrations of 20 to 50 ng/mL are typical for therapeutic use. Prescription methamphetamine exists; the fact sheets identify Desoxyn.
This is why the prescription wording carries so much weight. Without it, many patients would be over the limit on an ordinary school or work day.
The Valid Prescription Question
A person with a valid prescription for the stimulant in their blood is not covered by subsection (1)(f). The statute does not define "valid prescription," and the DUI definitions in MCA § 61-8-1001 do not either. The text leaves several situations unaddressed:
- medication taken from a prescription that has lapsed;
- a dose larger than prescribed;
- medication prescribed to a family member or friend.
The last one is the clearest risk. A person who borrows a tablet has no prescription of their own for it, and nothing in the text suggests another person's prescription counts.
When a Patient Can Still Be Charged
The impairment offense covers "any drug" (MCA § 61-8-1002(1)(a)), and a prescription is not a defense to it. The State would have to prove that the stimulant diminished the person's ability to operate a vehicle safely, and a positive test "does not, in itself, prove" that (MCA § 61-8-1018(1)(a)).
Stimulant impairment cases look different from alcohol cases. NHTSA lists indicators such as restlessness, talkativeness, body tremors, and anxiety for the stimulant category, which are also things a nervous driver may show at any traffic stop. A defense examines what the officer actually observed and whether it points to impairment or simply to a stressful stop. See our page on drug recognition evaluations.
Stimulants are also sometimes found alongside alcohol. The impairment offense covers a combination of alcohol and a drug.
Reading a Stimulant Lab Report
A toxicology report in a stimulant case can raise questions the summary line does not answer:
- Amphetamine with methamphetamine. NHTSA states that methamphetamine is metabolized to amphetamine, so a methamphetamine user's blood can contain both. Amphetamine with no methamphetamine is a different pattern.
- Other source drugs. NHTSA notes that several other drugs are metabolized to amphetamine and methamphetamine, and names benzphetamine, selegiline, and famprofazone.
- Isomers. The fact sheets note that the d and l forms of amphetamine can be separated with specialized laboratory techniques, which is necessary to distinguish certain pharmaceuticals.
- Blood, not urine. The per se offense is written in terms of an amount "as shown by analysis of the person's blood."
You are entitled to full information about a test given at an officer's direction (MCA § 61-8-1019(3)). Our guides to crime lab and toxicology reports and challenging a blood test explain what to look for.
Drivers Under 21 and Commercial Drivers
The under-21 provisions of the DUI statute set special rules for alcohol and THC only. The listed-drug limits are the same for every age. A college student is subject to the same 20 ng/mL amphetamine figure, and the same prescription wording, as any adult.
Subsection (1)(f) applies in a commercial motor vehicle as well as a noncommercial one. The commercial license consequences of a DUI are covered on our CDL DUI page.
This page explains Montana law in general as of the 2025 Montana Code Annotated. It is not legal or medical advice. Do not stop or change a prescribed medication without talking to your prescriber.