Cannabis and Driving: Why Feeling Fine Isn’t a Safety Test

Feeling Fine Doesn't Tell You Everything

One of the biggest problems with cannabis and driving is that impairment isn't always obvious to the person experiencing it.

You might feel calm and comfortable. You might feel completely capable of having a conversation or walking around your house. You might even feel like you're driving more carefully than usual.

None of those things is a reliable test of whether your reaction time, attention, coordination or judgment are operating at their normal level.

Research and public-health guidance have found that cannabis can slow reaction time and decision-making, impair coordination and alter perception. Those are all abilities that matter when you're driving.

And there's an important distinction here: feeling less impaired isn't necessarily the same thing as being unimpaired.

Tolerance can make the subjective effects of cannabis feel less noticeable. It doesn't give you a simple way to know that every skill involved in driving has returned to baseline. If tolerance itself is the concern, More Isn't Always Better looks at why feeling less affected does not always mean the underlying effects have disappeared.

That's one reason "I feel fine" isn't a very good safety test.

Driving Is More Complicated Than It Feels

Most of us don't think about everything we're doing when we drive.

We're watching the road while checking mirrors, reading signs, judging the speed of another vehicle, maintaining our lane, anticipating what pedestrians and other drivers might do and responding to unexpected changes.

Most of that happens automatically.

Until something doesn't.

A child runs toward the street. Someone suddenly changes lanes. Traffic stops ahead of you. A car pulls out of a driveway. An animal crosses the road. The driver in front of you slams on the brakes.

Those are the moments when a small change in reaction time or judgment can matter.

Cannabis can affect reaction time, coordination, attention and perception. The CDC specifically notes that cannabis can impair skills needed for safe driving, and NHTSA identifies slowed coordination, judgment and reaction times as concerns with marijuana-impaired driving.

You don't have to feel dramatically intoxicated for those things to matter.

Edibles Make the Question Even Harder

The way you use cannabis matters.

Smoking or vaping generally produces effects more quickly, while edibles take longer to produce their full effects and can last considerably longer. That difference makes it especially easy to misjudge an edible experience.

Someone may take an edible, feel nothing after a short period of time and decide they're fine. Then the effects begin building later.

That can create a dangerous situation if driving was part of the plan.

This is one reason harm reduction starts before consumption. If you know you're going to use an edible, think about transportation before you take it rather than trying to decide later whether you feel capable of driving.

The same basic principle applies to other cannabis products: don't assume that because you use them regularly, you can predict exactly when you're safe to drive.

"But I Have a High Tolerance"

This is one of the more understandable arguments from experienced cannabis users.

Someone who uses cannabis regularly may genuinely experience less noticeable intoxication than someone who rarely uses it. That difference matters when talking about how a person experiences cannabis.

But tolerance doesn't turn cannabis into a non-impairing substance.

It also doesn't give you a reliable personal formula like, "I use this much every day, so I'm always safe to drive after this amount."

The relationship between THC concentration and actual impairment is complicated. THC can remain detectable in the body after the noticeable effects have faded, and blood THC concentration doesn't provide a simple, universally reliable measurement of how impaired an individual driver is at a particular moment.

That means two different questions need to stay separate:

"Do I still feel high?"

and

"Am I capable of safely handling an unexpected situation behind the wheel?"

The first question is something you can answer subjectively.

The second is much harder to answer from inside your own head.

Cannabis and Alcohol Are Not a Good Combination

If there's one part of this conversation that deserves an especially clear warning, it's mixing cannabis and alcohol. Our guide to cannabis and alcohol together explains why that combination can be more impairing and less predictable than either substance alone.

Using the two together can increase impairment compared with using either one alone.

This is not the time to rely on tolerance or personal experience.

If you've been drinking and using cannabis, don't drive.

Arrange a ride. Stay where you are. Have someone else drive who hasn't used impairing substances. Whatever solution keeps you out of the driver's seat is the better solution.

What About CBD?

CBD deserves a little nuance here.

CBD itself isn't generally associated with the same intoxicating effects as THC, but that doesn't mean every CBD product is automatically safe to use before driving. Some products can contain THC, labels aren't always perfectly predictive of what's actually in a product and CBD products may also have other ingredients or effects worth considering.

The CDC notes that cannabis products, including CBD products, may contain small amounts of THC.

There's also another important point: medications and other substances can affect driving ability too. Prescription and over-the-counter medications can cause drowsiness, dizziness, impaired vision or impaired coordination, and combining substances can change how you feel and function.

So don't think of this as a cannabis-only issue.

Think of it as a know what you're putting into your body before you get behind the wheel issue.

There Isn't a Magic THC Number

This is another place where cannabis doesn't fit neatly into the same box as alcohol.

With alcohol, blood alcohol concentration has a much more established relationship to impairment, which is why BAC limits can be used in driving laws.

THC doesn't work the same way.

THC levels can remain detectable after the noticeable effects of cannabis have decreased, particularly in people who use cannabis regularly. Researchers and traffic-safety organizations have therefore cautioned against treating a particular THC concentration as a simple measurement of whether someone is currently impaired.

That doesn't mean THC isn't relevant.

It means a lab number shouldn't be treated as a personal "I'm good to drive" calculator.

And laws are a separate issue altogether. Cannabis laws and impaired-driving laws vary by state, so knowing that cannabis is legal where you live does not mean driving after using it is automatically legal.

A Better Harm-Reduction Approach

The simplest way to approach cannabis and driving is to plan around the possibility that you might be impaired rather than trying to prove to yourself that you're not.

If you're planning to use cannabis, make transportation part of the plan.

If you're going somewhere and know you'll need to drive home, consider waiting until you're home before using cannabis.

If you've already used cannabis and you're questioning whether you're okay to drive, that's a pretty good reason not to drive.

Get a ride. Call someone you trust. Use a rideshare service. Stay where you are. If you're with friends, decide ahead of time who will remain sober and drive.

And if someone you care about is about to drive after using cannabis, don't be afraid to speak up.

You don't have to shame them or turn it into an argument about cannabis.

You can simply say, "Let me drive. We'll figure the rest out."

That's harm reduction too.