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Avoiding Adverse Drug Interactions

#FlySafe GA Safety Enhancement Topic

FAA Safety Briefing
Cleared for Takeoff
6 min readOct 26, 2020


Impairment from medication, particularly over-the-counter (OTC) medication, has been cited in a number of accidents in general aviation (GA). In a 2011 study from the FAA Civil Aerospace Medical Institute’s Toxicology Lab, drugs/medications were found in 570 pilots (42%) from 1,353 total fatal pilots tested. Of the pilots with positive drug results, 90%, were flying under 14 CFR part 91.


What’s the Problem?

As you know, some drugs and medical conditions can compromise a pilot’s ability to control the aircraft and/or adversely affect judgment and decision-making. When the FAA reviews an application for a medical certificate, it endeavors to ensure that the risk from any medical condition and/or treatment has been adequately mitigated for safe flight. Some airmen fail to disclose all conditions and medications to their Aviation Medical Examiner (AME). Consequently, the AME does not have the opportunity to suggest steps to enhance safety. Both the undisclosed condition(s) and the treatment can endanger you, your passengers, and the public.

Photo by Aliona Gumeniuk on Unsplash

According to a 2015 CDC study, nearly 74% of doctor office visits resulted in drug therapy and 24% of the U.S. population had 3 or more prescriptions. Many medications have unexpected interactions with other prescription medications as well as over the counter medications (OTCs), supplements and herbals. For example, antihistamines can adversely react with some prescription drugs used to treat high blood pressure. Some foods and medications can increase or decrease the clearance of other drugs. For example, grapefruit or grapefruit juice can interfere with the metabolism of statins and cause dangerous side effects. Many such interactions can be exacerbated in the aviation environment. Accordingly, it is important to disclose all medications you are taking to your AME. Here’s a resource from the FDA you can use to learn more about adverse food and drug reactions, as well as some helpful information from the American Heart Association. These resources describe some but by no means all, adverse drug and food interactions.

Differentiating the detriment from the underlying condition(s) and that from the treatment is frequently challenging for accident investigators. It is clear, though, that a failure to disclose does not eliminate the risk.

How Long?

Graphic of airplane and pills.

Whether you are taking a new medication, which should be safe to fly with, or a medication known to be incompatible with flight, you face the question of how long to wait before you resume flying after starting or stopping, respectively, the medication? Every medicine is different, but a good rule of thumb is 5 times the half-life of the medication or by the dosing interval (if the half-life information is unavailable); use whichever has the longer interval. If a medication says to take it 4 times per day, the dosing interval would be 6 hours. Therefore the wait time after the last dose would be 30 hours (6 hours x 5 = 30 hours). Other medications may have longer or shorter intervals which is why it’s important to talk to your AME. This interval provides a reasonable ground trial for non-impairing medications, such as aspirin, and a reasonable wash-out for medications that are impairing, such as diphenhydramine.

Common Sedatives

Many medications are potentially impairing; some of the most common are antihistamines. These medications are used for allergies, “colds”, and in sleep aids. According to an NTSB study, sedating antihistamines are the most commonly detected medication in fatal accidents. Diphenhydramine, the active ingredient found in many medications like Benadryl, Tylenol PM, or Unisom, is often used as an OTC sedative. Many pilots are unaware that you should not fly for 60 hours after taking diphenhydramine. If you suffer from allergies, consider a non-sedating antihistamine such as loratadine instead.

Photo by Michał Parzuchowski on Unsplash

Although seen less commonly, other drugs can also cause sedation as well as cognitive impairment. These include some antidiarrheal drugs (often due to opioids), anti-seizure drugs, and some antidepressants. Frequently, there are options that are not impairing or disqualifying and are acceptable to the FAA (assuming that the underlying condition is safe for flying). We suggest you work with both your primary care doctor and your AME when considering use of these and other medications. However, AMEs should know more which medications are permissible in the aviation environment, whereas a primary care doctor might not.

Where Can I Get More Information?

A good place to start is the new OTC medication guide listed below. The guide provides pilots with a list of commonly used OTC medications that are generally safe (GO) and those that are not (NO-GO). Take a close look at this list because some medications we regard as equivalent may have very different impacts on safety. Be sure to check out the “Do Not Issue/Do Not Fly” section too. You can also find good information on drugs through trusted government sites like the National Institute of Health’s Medline site at medlineplus.gov. This site lists both generic and trade names along with side effects and warnings for almost every drug out there.

What to Look For

The Food and Drug Administration (FDA) requires standard labeling for all OTC medications. These standard medication labels include the active ingredients, directions for use, and highlight potential side effects like drowsiness in the warning section. Be sure to check out our OTC medication guide (PDF download).

Drug label.

Supplements may also interact with OTC and prescription medications to cause impairment. It’s also important to note that supplements may have similar labels, but are not regulated by the FDA, and therefore do not need to meet a specific standard. This is especially concerning for cannanbidiol (CBD) products. The CBD industry has widely varying quality control and labeling leading to significant discrepancies from package labels including much higher tetrahydrocannanbidiol (THC) — the component that gets one “high” — levels than disclosed. This can cause both impairment and possibly a positive drug test. Therefore, the FAA strongly discourages the use of CBD products by airmen.

Read more about CBD at https://spark.adobe.com/page/vEq0BNqJBHTIq/.

Watch Pilot Minute: Why is it important to be careful with over-the-counter cold and sleep medications?

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FAA Safety Briefing
Cleared for Takeoff

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