Ask Dr. Hallberg: Driving under the influence of Rx

Many people know about the dangers of driving while intoxicated, but law enforcement officials and health experts say that driving while under the influence of certain prescription medications could be just as dangerous.

MPR News medical analyst Dr. Jon Hallberg joined All Things Considered's Tom Crann on Wednesday to discuss the dangers of "drugged driving."

Hallberg is a physician in family medicine at the University of Minnesota and medical director of the Mill City Clinic in Minneapolis.

Tom Crann: There are a lot of prescription medications that can impair our ability to react quickly on the road. Our conversation is prompted by a New York Times article about the problems that police and prosecutors are having with people driving while impaired by medications. Sometimes those medications are prescribed and being taken appropriately by people. Did this surprise you?

Dr. Jon Hallberg: Well, not really. I think we're so well accustomed to the idea of, "Don't drink and drive," but I think there are a lot of medications out there that make people more tired than they realize. And it's not the obvious meds all the time. We know that if you're on a sleeping medication or a narcotic pain medication, obviously you're going to be tired. But medications like muscle relaxants and antihistamines are less obviously sedating. So I think people take them sometimes and are really surprised at how tired they get.

Crann: So, which medication's side effects are the most worrisome when it comes to operating a vehicle, for example?

Hallberg: It's puzzling to us sometimes. We think, 'Well, I'm taking a drug to dry up my nose,' or 'I'm taking something to relax my muscles,' but in fact, they're all working in the brain, largely. Or at least they have secondary effects on the brain. And anything that does that, it decreases your reaction time so that you may not be able to avoid an accident as quickly as you might have. They can simply make you tired. It makes it very, very difficult, when you're on those long stretches of road, to stay awake, frankly.

I think a lot of times we're not aware of all the medications that people are on. And so there may be other over-the-counter things that can make people tired as well.

Crann: If a doctor prescribes it and doesn't specifically warn you about, let's say, driving a car, is it always safe to assume you're all right?

Hallberg: It is really a tricky thing. I think that every single time we prescribe a drug we should be telling patients about potential side effects. I think most of us know several of the side effects of most of the common drugs, but there are a lot of medications out there that are new. We're really not fully aware of things. I can list two, three, four things usually on most meds that I prescribe, but honestly, I don't know all the side effects.

So this is where we really rely on our pharmacy colleagues. In fact, I was just checking with one and asking, 'How do those labels get attached to the bottles?' And luckily, that's mostly computer-generated now, so that if I prescribe a medication, and it's filled at a pharmacy, and sedation is one of the side effects.

Crann: It spits out the label automatically.

Hallberg: It spits out, and you put it on. So I think it's really imperative that patients look at the bottle, look at those, and take those warning labels very seriously.

Crann: Can you ever totally predict reactions to medication?

Hallberg: No, and in fact when the list comes out of all the common side effects, and there are also some uncommon side effects listed, it doesn't mean that people might not have something that's not on the list. I always remind people that any medication is capable of causing any number of side effects. People should be aware of that. Then it's sort of a 'buyer beware.' If you take a pill, if you take a chemical, we're not exactly sure how you're going to react to it.

Crann: Okay, narcotic pain medications or sleeping medications, we might expect them to impair our ability to drive or operate heavy machinery, as they always say. But what sort of classes of medications might we not be thinking about that we should?

Hallberg: The two that jump to mind immediately would be the antihistamine category. And we're all very excited because there are new, non-sedating antihistamines, like Claritin, for example, and Zyrtec. But what that means is that something like 90 percent of the people who take it, don't get fatigued. But that means maybe ten percent do. So I think it's falsely reassuring that you're not going to get sedation with that.

Crann: It doesn't mean everybody.

Hallberg: That's right. And then there are different categories of muscle relaxants. Some, like Flexeril, are notorious for making people feel very strange, actually. And so we give a very small dose of that. Others aren't supposed to make you as tired, but may. And then some medications, some of the anti-inflammatory medications, for example, can make people fatigued in ways they weren't expecting.

Crann: Really? You mean something like Advil or a pain reliever?

Hallberg: Yes, absolutely. Some people will find that if they have trouble sleeping, they will take something like Advil or even Tylenol, and it just seems to make them kind of relaxed or feel a little sleepy. Most of us don't get that effect, but some do.

Crann: In the health care profession, whether it's in the clinic or at the pharmacy counter, are people doing what they need to do enough to get the word out to people?

Hallberg: I think so. I don't know what you can do beyond telling people and then posting it right on the bottle that, frankly, you have to open up every time you take one of those medications. The only thing that's better is there are some medications that are so potentially harmful. Accutane is an acne medication, and if a woman is pregnant, it can cause birth defects.

And so every time you pop one of those pills, you have to push it out of a blister pack that has a no-pregnancy sign. So every single time it reminds you. That's taking it to an extreme. I think that that's not very realistic for all medications that might cause sedation.

Crann: Well, Jon, thanks for a little insight into the side effects of prescription medication.

Hallberg: It was my pleasure, Tom. Thank you.

(Interview transcribed and edited by MPR reporter Madeleine Baran)

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