Drug and medication impaired driving: know your risk before you drive
How cannabis, medicines and other drugs affect driving and what to ask your pharmacist
Picture a driver with a bad cold who takes a nighttime cold medicine at midnight. At 6:30 a.m. he leaves for work, a little foggy but sure he is fine. Now picture a woman at a party who eats a cannabis gummy, feels nothing after 45 minutes and drives home. Neither feels drunk or high, yet both may be driving at the worst possible moment.
Drug impairment is harder to judge than alcohol because there is no breath number, effects vary by person and some drugs peak hours later. In a National Highway Traffic Safety Administration (NHTSA) study, more than half of seriously or fatally injured drivers tested positive for alcohol or other drugs [1].
This guide takes a toxicologist’s and pharmacist’s view of how drugs affect driving, how long to wait and what to ask.
How drugs interfere with the skills driving needs
Driving asks your brain to steer, scan, judge gaps and react, all at once. Toxicologists sort drugs by how they disrupt those jobs.
- Depressants slow the brain and include alcohol, sleep medicines, opioids, sedating antihistamines and benzodiazepines (anxiety medicines such as alprazolam). Expect drowsiness, slow reactions and lane drifting.
- Stimulants such as cocaine and methamphetamine rev the brain up. NHTSA notes they can make drivers aggressive and reckless [2].
- Cannabis fits neither group neatly. NHTSA reports it impairs motor skills, lane tracking and thinking. It also hurts your ability to multitask [2].
The U.S. Food and Drug Administration (FDA) flags side effects that matter behind the wheel: sleepiness, blurred vision, dizziness, slow or clumsy movement, fainting and trouble focusing [4].
The effect depends on the dose, the timing and what else is in your system. So a friend’s experience is no guide for you.
How often drugs show up in serious crashes
NHTSA tested blood from 7,279 seriously or fatally injured road users at 7 trauma centers and 4 medical examiner offices [1].
Comparison compiled by Safety Behind the Wheel Foundation
Drivers who tested positive, September 2019 to July 2021
| Substance category | Seriously injured drivers | Drivers who died |
|---|---|---|
| Any alcohol or drug | 54.4% | 68.8% |
| Alcohol | 21.6% | 38.9% |
| Cannabis (active THC) | 25.0% | 31.7% |
| Opioids | 8.6% | 13.0% |
| Stimulants | 9.8% | 12.6% |
| Sedatives | 7.5% | 7.2% |
| 2 or more categories | 18.1% | 33.9% |
Source: NHTSA, DOT HS 813 399 [1]. “Sedatives” includes benzodiazepines, muscle relaxants such as carisoprodol and cyclobenzaprine, and sleep aids such as zolpidem.
A positive test shows a drug was present, not that it caused the crash [1]. The sites were not a national sample. As of October 2026, we found no newer NHTSA estimate of this kind. Still, about 1 in 3 drivers who died had 2 or more substance categories on board [1].
Cannabis and driving: what the research shows
THC (tetrahydrocannabinol) is the main intoxicating compound in cannabis. In lab and simulator studies, it slows reaction time and makes lane position less steady [6]. It also weakens divided attention, the ability to handle more than one task at once [6].
The crash risk picture is mixed. A review of 26 studies found 32% higher odds of crash involvement among drivers who used cannabis [7]. But a more rigorous study found no added risk once age, sex and alcohol were accounted for [7]. Across 5 Western states, the Insurance Institute for Highway Safety (IIHS) linked legal retail cannabis to a 6% rise in injury crash rates [7].
Why a THC number cannot tell you if you are impaired
Blood alcohol rises and falls roughly in step with impairment, but THC does not. After smoking, blood THC peaks right away and drops 80% to 90% within 30 minutes [6]. Yet in one study NHTSA describes, impairment peaked about 90 minutes after smoking, after THC had already fallen more than 80% [6]. Some studies have found THC in the blood 30 days after use [6].
The AAA Foundation for Traffic Safety tested this with data from drivers arrested for impaired driving. No THC level from 1 to 10 nanograms per milliliter lined up reliably with how drivers did on roadside sobriety tests [8]. Among cannabis positive drivers, 70% were below 5 nanograms, a limit some states have used [8]. The researchers concluded that a numeric THC limit cannot be scientifically supported [8]. A 2022 randomized trial also found that blood THC did not track driving performance [3].
How long to wait after cannabis
No federal agency sets a safe waiting time. No home test can clear you to drive.
- Smoked or vaped: NHTSA’s report to Congress describes impairment for 2 to 3 hours after smoking [6]. In the 2022 trial, 191 regular users smoked as much as they liked. Their simulated driving was worse than placebo at 30 minutes and 1.5 hours, borderline at 3.5 hours and normal by 4.5 hours [3]. Many felt ready to drive while their scores still showed impairment [3].
- Edibles and drinks: The Centers for Disease Control and Prevention (CDC) notes an edible can take up to 2 hours to kick in [9]. The slow start can lead people to take more than they meant to [9].
The safest clinical advice: if you use cannabis, do not plan to drive that day. After edibles, strong products or cannabis with alcohol, sleep before you drive. Medical cannabis users should ask their clinician about timing.
Medicines that can affect your driving
Most medicines do not stop people from driving safely. But FDA lists several types that can, including antihistamines, sleep aids, opioids, benzodiazepines, muscle relaxants and antidepressants [4]. Antipsychotics, antiseizure medicines, stimulants and CBD products are on it too [4].
Research reviewed by NHTSA adds detail [10]:
- Sedating antihistamines. Older ones such as diphenhydramine have a small link to crashes. But nondrowsy ones such as cetirizine do not appear to raise crash risk [10]. FDA notes antihistamines can slow reactions even if you do not feel drowsy [4].
- Benzodiazepines. In lab studies they make it harder to keep the car centered. Risk depends on the drug, dose, time since the dose and whether alcohol or opioids are added [10].
- Opioids. Most experiments show some loss of psychomotor skill, the link between what you see and how you move, though crash studies are mixed [10].
- Antidepressants. Newer types such as SSRIs show little or no link to crash risk, especially once a person has adjusted. Older and sedating types, such as tricyclics and trazodone, may be different [10].
- Stimulants. A review cited by NHTSA found higher odds of fatal crashes among drivers on amphetamines or cocaine [10]. If you take a prescribed ADHD stimulant, take it exactly as directed.
The condition matters too, since depression and other mental health conditions are crash risk factors on their own [10].
Sleep medicines and the morning after
In 2013, FDA found zolpidem levels could stay high enough the next morning to impair driving [11]. It lowered the starting dose for women to 5 mg (6.25 mg for extended release) and advised extended release users not to drive the next day [11].
FDA now cautions that all insomnia medicines can impair driving the morning after [12]. The Z drugs (zolpidem, eszopiclone and zaleplon) also carry a warning about complex sleep behaviors, such as driving while not fully awake. These can happen even after the first dose. If one does, stop the drug and call your health care professional right away [12].
Mixing substances: when effects stack up
NHTSA warns that using 2 or more drugs at once, including alcohol, can amplify the effects of each [2]. Depressants act on overlapping brain systems, so their effects can add up or even multiply.
- Alcohol plus sleep medicine: FDA says not to drink before or while taking a Z drug [12].
- Benzodiazepine plus opioid: FDA warns this pairing has caused severe breathing problems and death [5].
- Alcohol plus cannabis: In a simulator study NHTSA describes, each made lane position less steady. Together, their effects added up [6].
Timing does not prevent an interaction: a long acting morning pill can still be active at dinner. Coffee does not remove a sedating drug from your body.
Reading labels and handling the first dose
Read the Drug Facts label on over the counter medicines and the warnings on prescription packaging [4]. NHTSA notes that a warning about operating heavy machinery includes driving [2]. Check nighttime or “PM” products for an added sleep ingredient.
FDA advises taking a new medicine for the first time when you will not need to drive [4]. Use the same caution after a dose increase or an added medicine.
Warnings seem to help. In a 2021 AAA Foundation survey, about half of drivers had used a potentially impairing medicine in the past 30 days [13]. Nearly half of those users drove within 2 hours of a dose. Drivers who had been warned about a medicine were 18% less likely to drive that soon after taking it [13].
Medicine or drug type: effects and what to do
Comparison compiled by Safety Behind the Wheel Foundation
| Medicine or drug type | How it can affect driving | What to ask or do |
|---|---|---|
| Cannabis, smoked or vaped | Slower reactions, lane drifting, weaker divided attention [6] | Do not plan to drive the same day |
| Cannabis edibles and drinks | Same effects, but may start up to 2 hours later [9] | Wait until after a full night’s sleep |
| Sedating antihistamines (e.g., diphenhydramine) | Slower reactions, foggy thinking, even without feeling sleepy [4] | Ask about a nondrowsy option |
| Sleep medicines (zolpidem, eszopiclone, zaleplon) | Next morning impairment; rare sleep driving [12] | Ask when it is safe to drive after a dose |
| Benzodiazepines | Trouble keeping the car centered [10] | Never mix with alcohol or opioids; do not stop suddenly [5] |
| Opioid pain or cough medicines | Some loss of psychomotor skill [10] | Avoid driving after the first dose or a dose change |
| Muscle relaxants | Listed by FDA as possibly impairing; counted as sedatives in crash testing [1, 4] | Ask how long effects last |
| Older or sedating antidepressants | May carry more crash risk than newer types [10] | Ask whether a bedtime dose makes sense |
| Antiseizure medicines, antipsychotics | May affect driving; evidence varies [10] | Ask about driving at each dose change |
| Cocaine, methamphetamine | Aggressive, reckless driving [2] | Do not drive; plan a sober ride |
| Any of these plus alcohol | Effects can amplify [2] | Ask your pharmacist about your exact mix |
Older adults, caregivers and multiple medicines
In the 2021 AAA Foundation survey, 63.3% of drivers using 2 or more potentially impairing medicines drove within 2 hours of a dose. For those using 3 or more, the share was 70.8% [13].
- Do a brown bag review. Once a year, bring every pill bottle, vitamin and supplement to your pharmacist. FDA advises telling your health care professional about all of them [4].
- Caregivers, watch for changes. New drowsiness, confusion or close calls after a medicine change are worth a call to the prescriber.
Questions to ask your pharmacist or clinician
What to do if...
- You already took something and need to go somewhere. Get a ride or delay the trip. Next time, plan a sober driver ahead [2].
- You feel effects while driving. Pull over somewhere safe and call for a ride.
- A friend plans to drive after using. Do not let them drive. Offer a ride or a couch [2].
- You are a parent of a teen. Talk about cannabis and medicines along with alcohol. Promise a no questions asked pickup.
Frequently asked questions
How long after using cannabis can I drive?
No timer can tell you for sure. In a 2022 trial, driving took 3.5 to 4.5 hours to recover after smoking [3]. Edibles can take 2 hours just to kick in [9]. The safest plan is not to drive that day.
Can I get a DUI for driving on my prescription medicine?
Yes, because driving impaired by any drug, legal or illegal, breaks the law in every state [2]. A valid prescription does not protect you if the medicine impairs your driving.
Is it safe to drive after taking Benadryl?
Diphenhydramine, the antihistamine in many Benadryl products, can slow your reactions even if you do not feel sleepy [4]. Nondrowsy antihistamines do not appear to raise crash risk [10]. Ask your pharmacist which option fits you.
Can I drive the morning after taking a sleeping pill?
Maybe not, since FDA cautions that all insomnia medicines can impair driving the next morning [12]. Ask your prescriber how many hours you need between a dose and driving.
Does CBD affect driving?
It can, since FDA lists cannabis and CBD products among those that may make driving unsafe [4]. Do not drive until you know how a product affects you.
The bottom line
Recommendation from Safety Behind the Wheel Foundation
Treat any new medicine, dose change or cannabis use as a reason to pause before driving. Take first doses at home and never mix sedating substances with alcohol. When in doubt, ask your pharmacist and get another ride.
Related articles
- Alcohol impaired driving: know the risks and plan a sober ride home
- Drowsy driving: warning signs, hidden risks and what really works
- Medical conditions and driving: why function, not diagnosis, decides
- Older driver safety: how to keep driving safely and confidently
- Medical readiness to drive: a health guide for new drivers before the permit
Sources and further reading
- 1Thomas FD, Darrah J, Graham L, et al. Alcohol and Drug Prevalence Among Seriously or Fatally Injured Road Users. NHTSA, DOT HS 813 399. December 2022. rosap.ntl.bts.gov/view/dot/65623
- 2National Highway Traffic Safety Administration (NHTSA). Drug-Impaired Driving. Accessed October 2, 2026. nhtsa.gov/risky-driving/drug-impaired-driving
- 3Marcotte TD, et al. Driving Performance and Cannabis Users’ Perception of Safety: A Randomized Clinical Trial. JAMA Psychiatry. 2022. PMID 35080588. pmc.ncbi.nlm.nih.gov/articles/PMC8792796
- 4U.S. Food and Drug Administration (FDA). Some Medicines and Driving Don’t Mix. Consumer update. March 12, 2024. fda.gov/consumers/…/some-medicines-and-driving-dont-mix
- 5FDA. FDA Requiring Boxed Warning Updated to Improve Safe Use of Benzodiazepine Drug Class. Drug Safety Communication. September 23, 2020. fda.gov/drugs/…/benzodiazepine-drug-class
- 6NHTSA. Marijuana-Impaired Driving: A Report to Congress. DOT HS 812 440. July 2017. nhtsa.gov/…/812440-marijuana-impaired-driving-report-to-congress.pdf
- 7Insurance Institute for Highway Safety (IIHS). Alcohol and Drugs (research area overview). Updated August 2026. iihs.org/research-areas/alcohol-and-drugs
- 8Logan B, Kacinko SL, Beirness DJ. An Evaluation of Data from Drivers Arrested for Driving Under the Influence in Relation to Per se Limits for Cannabis. AAA Foundation for Traffic Safety. May 2016. aaafoundation.org/research/…per-se-limits-cannabis
- 9Centers for Disease Control and Prevention (CDC). Cannabis FAQs. Updated January 31, 2025. cdc.gov/cannabis/faq
- 10NHTSA. Countermeasures That Work: Drug-Impaired Driving, Understanding the Problem. Accessed October 2, 2026. nhtsa.gov/book/countermeasures-that-work/…/understanding-problem
- 11FDA. FDA Drug Safety Communication: FDA approves new label changes and dosing for zolpidem products and a recommendation to avoid driving the day after using Ambien CR. May 14, 2013. fda.gov/drugs/…/fda-approves-new-label-changes-and-dosing-zolpidem-products
- 12FDA. Taking Z-drugs for Insomnia? Know the Risks. Consumer update. March 6, 2024. fda.gov/consumers/…/taking-z-drugs-insomnia-know-risks
- 13Arnold LS. Use of Potentially Impairing Medications in Relation to Driving, United States, 2021. AAA Foundation for Traffic Safety. July 2022. aaafoundation.org/research/use-of-potentially-impairing-medications…
- 14NHTSA. Countermeasures That Work: Drug-Impaired-Driving Laws. Accessed October 2, 2026. nhtsa.gov/book/countermeasures-that-work/…/legislation-and-licensing/drug
- 15Governors Highway Safety Association (GHSA). Drug-Impaired Driving. Issue overview updated June 2026; laws reviewed June 2025 (table updated October 2025). ghsa.org/state-laws-issues/drug-impaired-driving
This article reflects the safety priorities of clinical toxicology, pharmacy and traffic medicine. It is general education, not medical or legal advice for any individual. Talk with your own clinician or pharmacist about your medicines. Laws and data change, so verify details with official sources. Reviewed October 2026.
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