Medications in pilots: toxicology and fitness to fly

A 38-year-old first officer seeks the company medical service late in the afternoon. She has had severe allergic rhinitis since the previous week. Last night, unable to sleep with a blocked nose, she took an allergy tablet she had at home, an old antihistamine that also helps with sleep. She says she woke up fine, feels no drowsiness at all and has a red-eye flight. She asks whether she can take another one tonight, "just to make sure she sleeps". The scene is fictional and was written for teaching.

This text uses the picture as a scenario for clinical reasoning. The question is not whether the medicine is good for rhinitis, but whether the person who took it is fit to function in a task that does not forgive error. The text is not a summary of any regulator's rules, it gives no doses and it does not indicate which medicine to use, because the sources read do not define that for pilots. If you play the case of the day on NEXO, you will recognize the type of trap: the clue that seems reassuring, "I'm not sleepy", is precisely the least reliable one.

Key points

• Common medications appear frequently in the toxicology of pilots killed in accidents.
• Diphenhydramine, a sedating antihistamine, is the drug most often found in these tests.
• Feeling alert does not guarantee that function is preserved.
• The condition being treated also enters the decision, not just the medicine.
• A practical rule uses multiples of the half-life to define the waiting time.
• Unreported medications are a real problem for those who assess the pilot.

Why medication and flight is a reasoning scenario

The case brings together a common medicine, a benign condition and a high-risk task. In general practice, the question would be whether the rhinitis has improved. Here, the question is different: what this medicine does to the attention, reaction time and judgment of someone who will be piloting in a few hours. The post on signs, symptoms and history reminds us that the history of medication use is part of the anamnesis, not an appendix.

What the scene teaches

The officer brings three clues. The first is the use of a sedating medicine, taken for two purposes at once. The second is the feeling of being fine. The third is the request to repeat the dose before a flight. The scenario trains you to separate what the person feels from what the evidence says about function, and to remember that the underlying condition also counts.

What accident toxicology shows

Since 1989, the medical institute of the American agency has analyzed samples from pilots killed in civil aviation accidents and published the prevalence of ethanol and drugs every five years, to know which substances were present (Chaturvedi and colleagues, report, 2015). These data are one of the few sources that show the real use of medications by pilots, not just what they declare.

Between 1999 and 2003, drugs or ethanol appeared in 52 out of every 100 of the pilots killed (Chaturvedi and colleagues, report, 2005). Between 2004 and 2008, the technical report of the same institute found drugs or medications in 42 out of every 100 of the pilots tested (Canfield and colleagues, report, 2011). The same report found medications without a prescription in 13 out of every 100 of the samples.

What changed over time

The series of studies every five years showed that, between the first and the fifth period, the presence of ethanol or drugs increased considerably, with a rise in both illicit drugs and prescription medications (Chaturvedi and colleagues, report, 2015). In the same study, the use of ethanol or drugs, together with underlying medical conditions, was considered a cause or factor in 5 out of every 100 of the accidents.

A study by the US National Transportation Safety Board, with data from 1990 to 2012, also found a trend of increased use of potentially impairing drugs and of medicines used to treat conditions that can themselves impair (NTSB, 2014). In amateur-built aircraft, prescription medications appeared in 26 out of every 100 pilots, against 16 out of every 100 in other aircraft (Chaturvedi et al., report, 2011).

What these numbers allow us to say

The studies discuss pilots who died, almost all of them in general aviation, and not airline pilots in general. They show the presence of the substance, not proof that it caused the accident. Even so, they support a clear clinical conclusion: the medications found are the same ones the general population uses, and many have the potential to impair performance (Chaturvedi et al., report, 2005).

The sedating antihistamine at the center of the scene

Diphenhydramine, a first-generation antihistamine, is the drug most often found in pilots killed in US civil aviation accidents (Canfield et al., report, 2011). The technical report notes that it is sold with and without a prescription and that it also appears in sleep aids and motion sickness remedies (Canfield et al., report, 2011). The safety board study adds that it is an ingredient in many allergy, cold and sleep formulas (NTSB, 2014).

A study devoted to first-generation antihistamines found these drugs in about 4 out of every 100 pilots killed in 1990 and in 11 out of every 100 in 2004, with an upward trend over the period (Sen et al., antihistamines, 2007). In most cases, the antihistamine was alongside other drugs or ethanol, and the safety board considered its use the cause of 13 accidents and a factor in another 50.

Why the sleep aid weighs on the flight

The same study explains the problem in one sentence: these antihistamines relieve allergy and cold symptoms, but cause drowsiness and sedation, effects that can impair performance (Sen et al., antihistamines, 2007). In the officer's case, she used the medicine precisely for that effect. What helps you sleep at night is the same effect that can get in the way in the early hours at the controls.

Pathophysiology: sedation without drowsiness

The most counterintuitive point of the topic is that a person can be impaired without feeling drowsy. The US agency's leaflet on medications and flying says the pilot can be impaired even while feeling alert and functioning normally, without noticing the impairment (FAA, Medications and Flying). The study on first-generation antihistamines notes that these medicines cause drowsiness and sedation, but the leaflet makes clear that the absence of perceived sleepiness does not guarantee preserved function.

The condition also impairs

The agency's leaflet notes that the decision involves two things: the effect of the medicine and the condition it treats (FAA, Medications and Flying). The rule of thumb is not to fly if the treated condition would make the flight unsafe should the medicine fail or wear off mid-flight. The same text notes that flying with congested upper airways is not a good idea, which places the officer's rhinitis inside the assessment, not outside it.

Reasoning: fit to function, not just "free of disease"

In ordinary clinical practice, the doctor asks whether the patient has a disease and whether the medicine is safe. In occupational medicine for safety, the question is whether the person is fit to function in that task, at that moment. This shift in the question is the heart of the scenario. The officer has no serious disease, but she may not be fit for the early-morning flight.

The post about base rate in diagnosis helps think about the problem from another angle. If diphenhydramine is the drug most often found in dead pilots, the question about over-the-counter medicines stops being a detail and becomes routine.

The differential diagnosis of "I'm not well enough to fly"

When a pilot may be impaired, the differential includes more than one cause, and they usually add up. The sources read allow us to put together this list.

• Sedative effect of the antihistamine taken the night before.
• The underlying condition itself, such as the nasal congestion of rhinitis.
• Association with other drugs or with ethanol, common in the studies.
• Use of other prescription medicines that the person did not report.
• Underlying medical condition that led to the use of the medicine.

Closing the case too early

The answer "I woke up fine, so everything is fine" is an example of ending the reasoning too soon, the error of stopping the search at the first acceptable explanation (Croskerry, 2003). The post about diagnostic pause shows how to do a simple check before concluding.

The five half-lives rule

The US agency's leaflet proposes a practical rule for the waiting time after the last dose of a medicine with potential for impairment: wait five times the maximum pharmacological half-life of the medication or, when that information does not exist, five times the maximum interval between doses (FAA, Medications and Flying). The same leaflet recommends never flying after taking a new medicine for the first time unless at least 48 hours have passed without side effects.

The technical report adds an important caveat: label recommendations based on half-life may not be adequate for aviation, because the performance required in flight differs from that of an ordinary task (Canfield and colleagues, report, 2011). The rule is therefore a conservative starting point, not a guarantee.

Reading the label as part of the exam

The leaflet advises the pilot to read the whole label and to look for words such as dizziness, drowsiness, blurred vision and a warning not to operate machinery or drive (FAA, Medications and Flying). If these effects are listed, the guidance is not to fly while using the medicine. If there is no access to the label, also do not fly. The effects may appear on one occasion and not another, so a good previous experience is no guarantee.

Clinical question	What the source says	Source
Is the medicine a sedating antihistamine?	Diphenhydramine is the drug most often found in deceased pilots	Canfield and colleagues, report, 2011
Does the person say they are not sleepy?	The pilot may be impaired even while feeling alert	FAA, Medications and Flying
How long to wait after the last dose?	Five times the maximum half-life or five times the interval between doses	FAA, Medications and Flying
Is the medicine new to the person?	Wait at least 48 hours without side effects	FAA, Medications and Flying
Is the condition being treated safe without the medicine?	Avoid flying if the condition would make the flight unsafe should the medicine fail	FAA, Medications and Flying
Are other substances present?	The antihistamine often appears with other drugs or ethanol	Sen and colleagues, 2007

What the toxicology exam measures and what it does not measure

Toxicology of deceased pilots is broad. Since 1990, the US agency's medical institute has tested blood, urine and tissue from pilots who died in accidents and looks for legal and illegal drugs, at therapeutic and abnormal levels (NTSB, 2014). The board's study considered only blood and tissue, because a drug present only in urine no longer has the potential to impair performance. This breadth explains why aviation has such detailed data on common medicines.

Even so, the exam has limits for clinical reasoning. It shows that the substance was present, but the concentration found does not always say how much it was impairing. In the study on antihistamines, blood concentrations ranged from below the therapeutic range to the toxic range (Sen and colleagues, antihistamines, 2007). Finding the medicine is a clue, not a verdict on the cause.

What remains unknown

The authors of the series published every five years point to a gap: the use of ethanol and drugs was studied in deceased pilots, but not in active pilots who were not involved in accidents (Chaturvedi and colleagues, report, 2015). Without this comparison group, it is not possible to say precisely how much the use of a medicine increases the risk of an accident. For the physician, the practical consequence is to use the data as a warning about what is common, not as a calculation of individual risk.

Why this matters in the office

The doctor who evaluates the first officer has no toxicology test, and does not need one. He has the history: which medicine, when the last dose was, why it was taken and whether the person intends to repeat it. The accident data serve to give weight to that history. If the medicine most often found in dead pilots is the same one she took to sleep, the question about the time of the last dose stops being bureaucratic.

The problem of the unreported medicine

A study reviewed the medical history of pilots killed in accidents who had residues of antidepressants in the selective serotonin reuptake inhibitor class. In 88 out of every 100 of them, neither the condition nor the medicine was declared in the medical examination records (Sen and colleagues, antidepressants, 2007). The accident investigation, on the other hand, found a history of a psychological condition or of use of the medicine in 12 of the 61 pilots.

The data has two clinical readings. The first is that the doctor cannot rely on the declaration alone. The second is that the fear of losing the license can keep the pilot from telling what he uses, which calls for an honest conversation without judgment. The post about affective bias shows how the relationship with the patient influences what he reveals and what the doctor sees.

How to ask

The question "do you take any medicine?" tends to get a "no". It works better to ask in a concrete way: what did you take for sleep, for allergy, for a cold, for motion sickness or for pain in the last few days. These are precisely the categories in which diphenhydramine appears (NTSB, 2014).

Management in the first officer's case

In the fictional case, the doctor has three tasks. The first is to treat the rhinitis in a way that does not compromise function. The second is to decide about the overnight flight based on the time since the last dose and on the waiting rule, and not on the feeling of being fine. The third is to explain why the second dose "to make sure of sleep" makes the problem worse instead of solving it.

The American agency's guide for examiners asks that the impact of the underlying disease on safety be considered first, and only then the frequency, duration and adverse effects of the medicine. For medicines in the "do not fly" category, the examiner should advise the pilot not to fly until a defined interval has passed after the last dose (FAA, guide for examiners).

The sources read do not bring a treatment regimen for rhinitis in pilots, and so this text does not indicate a medicine or a dose. The choice of treatment and the rules of each country remain with the attending doctor and with the examiner.

The flight time changes the calculation

The officer's flight is overnight, a few hours after the time at which she would take the second dose. The waiting rule on the leaflet counts from the last dose, and not from the first (FAA, Medications and Flying). A new dose at night, therefore, restarts the clock right before the flight. Explaining this in a concrete way, with the time of the dose and the time of the report for the flight side by side, usually helps more than a generic prohibition. The same conversation opens space to talk about sleep: if the rhinitis is taking away sleep, the problem to solve is the rhinitis, and not the lack of a sedative.

A possible conversation

• Explain that the medicine from the night before can impair even without sleepiness.
• Ask about all medicines used in the last few days, with and without a prescription.
• Assess whether the congestion, by itself, allows flying safely.
• Agree on the waiting time before returning to flight.
• Advise against a new dose of the same medicine before the flight.

Common errors in reasoning

The first error is to accept "I am not sleepy" as proof of preserved function, when the American agency's leaflet recalls that the pilot can be impaired even while feeling alert (FAA, Medications and Flying). The second is to look only at the medicine and forget the disease it treats. The third is to ask in a generic way and leave out the medicines without a prescription. The fourth is to treat the five half-lives rule as a guarantee, when the agency's own report says that the leaflet recommendations may not be enough for aviation.

These errors also appear outside aviation. Professional drivers, machine operators and doctors on the night shift face the same question. The post about burnout in medical school recalls that tiredness and the use of sleep medicines also appear among students and residents.

How NEXO helps train this reasoning

To use the case of the day as training, try three habits. Before the first guess, ask what medication the person may be taking. With each clue, ask whether it is a symptom of the disease or an effect of the treatment. After the result, note whether you trusted too much in what the person said they felt.

Three exercises with cases

List the possible medications. For each case, write down what prescription and over-the-counter medications the person could be using and what each one would explain.

Separate the disease from the medication effect. Next to each clue, write whether it comes from the condition or from the treatment.

Think about the task. Write whether the approach would change if the person had a safety role the next day.

The post about case-based learning in clinical practice shows how cases help cement this habit.

The limits on using the game are described on the NEXO economy page. If you research the teaching of clinical reasoning, the page for researchers explains how to get in touch. Professionals who write or review cases find information on the curator and creators pages, and institutions can learn about the proposal on the partnerships page.

Frequently asked questions

Do sedating antihistamines show up in pilots' toxicology?

Yes. Diphenhydramine is the drug most often found in pilots killed in US civil aviation accidents (Canfield et al., report, 2011).

Can a person be impaired without feeling sleepy?

Yes. The US agency's leaflet says the pilot can be impaired even while feeling alert and functioning normally (FAA, Medications and Flying).

Is there a rule of thumb for the waiting time?

Yes. The US agency's leaflet suggests waiting five times the maximum half-life or five times the dosing interval (FAA, Medications and Flying).

Does the disease being treated also factor into the decision?

Yes. The guidance is not to fly if the condition would make the flight unsafe should the medication fail (FAA, Medications and Flying).

Is it worth asking about over-the-counter medications?

Yes. Over-the-counter medications appeared in 13 out of every 100 samples from pilots killed between 2004 and 2008 (Canfield et al., report, 2011).

Final checklist

• I asked about medications for sleep, allergy, cold, nausea and pain.
• I included medications bought without a prescription.
• I considered that the feeling of being alert can be misleading.
• I assessed the underlying disease, beyond the medication.
• I calculated the time since the last dose.
• I used the waiting rule as a conservative starting point.
• I considered use with alcohol or other drugs.
• I talked without judgment to make it easier for the person to say what they use.
• I advised against a new dose of the sedating medication before the flight.
• I remembered that the rules on medications vary between countries.

Want to practice reasoning with progressive clues? Play the case of the day.

References

1. Canfield DV, Dubowski KM, Chaturvedi AK, Whinnery JE. Drugs and Alcohol in Civil Aviation Accident Pilot Fatalities From 2004-2008. Federal Aviation Administration, Office of Aerospace Medicine, DOT/FAA/AM-11/13. 2011. Technical report.
2. Chaturvedi AK, Craft KJ, Canfield DV, Whinnery JE. Epidemiology of Toxicological Factors in Civil Aviation Accident Pilot Fatalities, 1999-2003. Federal Aviation Administration, Office of Aerospace Medicine, DOT/FAA/AM-05/20. 2005. Technical report.
3. Chaturvedi AK, Craft KJ, Hickerson JS, et al. Prevalence of Ethanol and Drugs in Civil Aviation Accident Pilot Fatalities, 2009-2013. Federal Aviation Administration, Office of Aerospace Medicine, DOT/FAA/AM-15/13. 2015. Technical report.
4. Chaturvedi AK, Craft KJ, Hickerson JS, et al. Toxicological Findings in Fatally Injured Pilots of 979 Amateur-Built Aircraft Accidents. Federal Aviation Administration, Office of Aerospace Medicine, DOT/FAA/AM-11/21. 2011. Technical report.
5. Croskerry P. The importance of cognitive errors in diagnosis and strategies to minimize them. Acad Med. 2003. PMID 12915363.
6. Federal Aviation Administration. Guide for Aviation Medical Examiners: Pharmaceuticals, Do Not Issue and Do Not Fly. 2023. Guide.
7. Federal Aviation Administration. Medications and Flying. Pilot safety brochure. Brochure.
8. National Transportation Safety Board. Drug Use Trends in Aviation: Assessing the Risk of Pilot Impairment. Safety Study NTSB/SS-14/01. 2014. Study.
9. Sen A, Akin A, Canfield DV, Chaturvedi AK. Selective Serotonin Reuptake Inhibitors: Medical History of Fatally Injured Aviation Accident Pilots. Federal Aviation Administration, Office of Aerospace Medicine, DOT/FAA/AM-07/19. 2007. Technical report.
10. Sen A, Akin A, Craft KJ, et al. First-Generation H1 Antihistamines Found in Pilot Fatalities of Civil Aviation Accidents, 1990-2005. Federal Aviation Administration, Office of Aerospace Medicine, DOT/FAA/AM-07/12. 2007. Technical report.