We’re continuing our look at Potentially Driver-Impairing (PDI) medications, and this time we’re tackling something a lot of autistic teens and adults take without thinking twice about it: allergy and asthma medications.
When people talk about medication and driving, they usually focus on sleep medications, pain medications, or stimulants. Meanwhile, allergy season arrives, everybody starts reaching for antihistamines, (all of which can cross the blood-brain barrier to some degree) and nobody mentions that some of those medications can affect driving just as much as the more obvious suspects.
If you’re autistic, you’re already managing a lot of information behind the wheel. Traffic signals. Road signs. Speed. Other drivers. Pedestrians. Sensory input from every direction. The last thing you need is for an allergy pill to take the edge off your attention when you’re trying to navigate a busy intersection.
I started with a review of 16 controlled studies on this.1
Let’s start with the biggest offenders
The authors note that “first-generation antihistamines like diphenhydramine (Benadryl), triprolidine (Actifed), dexchlorpheniramine (Polaramine), and clemastine (Tavist) significantly impair driving performance after both one-time and repeated daily administration.” Folks, these are well-known for causing drowsiness, I mean who hasn’t heard of parents bragging about using Benadryl to make their kids go to sleep at night?
Studies keep showing the same thing—people don’t always realize how impaired they are on these older sedating antihistamines.1 They may feel functional while experiencing slower reaction times, reduced attention, and decreased driving performance.
The “persons of interest”
Second-generation antihistamines like cetirizine (Zyrtec), loratadine (Claritin), emedastine (Emadine—which is really more of an eye drop), and mequitazine (Primalan) can still affect driving for some people, it just doesn’t look as obvious as the older medications. There’s some evidence that people develop a bit of tolerance after 4-5 days of daily use. But “less noticeable” doesn’t always mean “gone.”
A cautionary note: although cetirizine (Zyrtec) is classified as a newer, less-sedating antihistamine, it tends to cause drowsiness more often than loratadine (Claritin) or fexofenadine (Allegra) in some people.
Here’s a little nugget: some research findings suggest that some antihistamines may produce higher blood concentrations or greater sedative effects in women1 ─that one surprised me!─ but individual responses vary widely. When it comes to driving, personal sensitivity to the medication is often a stronger predictor of impairment than sex alone.
Barely on the radar
There’s also a bit of good news in the data: “Third-generation antihistamines (fexofenadine (Allegra) and levocetirizine (Xyzal)) have been shown to produce no driving impairment after both one-time and repeated administration.”
As you’ve heard me say about almost every medication we’ve discussed so far in this chapter, your experience matters more than what’s printed on the box. It’s still possible for some people to experience fatigue, dizziness, or brain fog.
Then there are asthma medications.
For a lot of people, inhalers don’t change anything about driving—you take them and move on with your day. For others, rescue inhalers may cause shakiness, jitteriness, nervousness, or a racing heartbeat. If you’re already prone to anxiety or sensory overload, that extra stimulation can feel distracting.
Nobody is swerving across three lanes because of an inhaler. But if you’re already stressed, overloaded, and trying to process too much at once, a little extra jitteriness is unwelcome.
But wait, you might say, you can’t go without your allergy meds. What’s the effect on your driving when allergies or asthma are poorly controlled?
Constant sneezing, congestion, itchy eyes, and disrupted sleep can reduce alertness all by themselves. Uncontrolled allergies can be exhausting. Asthma flare-ups can leave you tired, uncomfortable, and struggling to focus. Sometimes the symptoms create more driving difficulty than the medication treating them.
So, pay attention to how you feel after taking a new medication. Notice whether you’re more tired, more jittery, more distracted, or less patient than usual. If you can, try it out in lower-stress situations first—short drives, familiar routes, that kind of thing—before you end up in heavy traffic or a long unfamiliar trip.
Here’s another point I beat into the ground: ask questions
Talk to your doctor. Talk to your pharmacist. Ask specifically about driving. Ask whether a medication is known to cause drowsiness, dizziness, slowed reaction time, or nervousness. If you don’t like how the allergy medication your doctor recommended makes you feel, switch to a different one. (These are all generally available over-the-counter, so you can play around with them a bit.)
If you’re on the spectrum, you’re probably already dealing with multiple medications on board ─see my article on polypharmacy here─ so we’ll all be safer when we pay attention to how our meds affect our thinking and reflexes behind the wheel.
Want to See the Research?
- Antihistamines and driving ability: evidence from on-the-road driving studies during normal traffic Joris C Verster, Edmund R Volkerts Ann Allergy Asthma Immunol. 2004 Mar;92(3):294-303; quiz 303-5, 355. doi: 10.1016/S1081-1206(10)61566-9. https://pubmed.ncbi.nlm.nih.gov/15049392/?utm_source=chatgpt.com