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How Pilots Can Safely (and Legally) Use Antihistamines and Other Sleep-Inducing Medications

How Pilots Can Safely (and Legally) Use Antihistamines and Other Sleep-Inducing Medications

It is a common misconception that over-the-counter (OTC) drugs are not only safe, but are also FAA approved to use while on flight status. After all, if a medication were harmful, wouldn’t it require a prescription? Not necessarily so! Many OTC drugs can actually be quite dangerous, especially when used inappropriately in relation to flying. In my practice, I find that pilots frequently misuse certain OTC medications, not understanding the FAA restrictions, and more importantly, the potential dangers to flight safety. Some of these medications are marketed for both allergies and sleeping aides, so you can be sure there are not only FAA rules that go with their use, but more importantly, safety principles.

In the OTC world, the most commonly sold anti-allergy medications are made from “first-generation” antihistamines, such as diphenhydramine and chlorpheniramine. They help reduce the unpleasant symptoms of itching, watery eyes, runny noses, sneezing, and hives caused by seasonal or environmental allergies. Diphenhydramine (also known by the brand name Benadryl) can be a life-saving drug when used to treat severe allergic reactions, as can occur from bee stings or food allergies in highly sensitized individuals. However, these antihistamines also produce significant drowsiness in most people, and because adverse effects on mental functioning can last even longer than perceived drowsiness, the FAA warns that pilots should ground themselves for at least 5 times the drug’s half-life (or 5 times the maximum dosage interval if half-life information is not available).  For diphenhydramine, that means 60 hours!

Because these antihistamines are found in many OTC cough and cold remedies, pilots often take them inadvertently. An airman should always carefully review the ingredients of such multi-symptom formulas, making sure that they do not include any compounds to control itching, sneezing, or to induce sleep. Decongestants (pseudoephedrine) are generally OK to use during flight status, but first-generation antihistamines are not!

After several years as prescription medications, a few “second generation” antihistamines are now available over the counter. The nonsedating antihistamines loratidine (Claritin), desloratidine (Clarinex) and Fexofenadine (Allegra) may be used while flying if, after an adequate initial trial period, symptoms are controlled without adverse side effects. There are others of this category available by prescription, or OTC but not all are currently FAA approved.  Just because your personal physician prescribes it, doesn’t mean that the FAA considers it safe for flight. For example, cetirizine (Zyrtec) is not.

Whether OTC or prescription, the FAA requires waiting periods after taking medications that produce drowsiness. These waiting periods are based on how long the drug takes to be eliminated from the body – defined as “half life” – which is the time that half the drug is metabolized and eliminated by the body.  The longer the half-life, the longer the potential side effects. If the half-life is not available, the alternative is to determine the waiting period based on how often the drug is to be taken – or its dosing interval. The longer the half-life, the further apart the dosing interval.

According to the FAA, sedating medications should not be taken until:

  • • At least five maximal dosing intervals have passed. For example, if the medication is taken every 4-6 hours, wait 30 hours (5×6) after the last dose to fly, or,
  • • At least five times the maximum terminal elimination half-life has passed. For example, if the medication half-life is 6-8 hours, wait 40 hours (5×8) after the last dose to fly.
    • • At least five maximal dosing intervals* have passed. For example, if the medication is taken every 4-6 hours, wait 30 hours (5×6) after the last dose to fly, or,
    • • At least five times the maximum terminal elimination half-life has passed. For example, if the medication half-life* is 6-8 hours, wait 40 hours (5×8) after the last dose to fly.


Now, let’s get to the category of sleeping medications. In the OTC world, the drowsiness produced by these first-generation antihistamines is capitalized upon, and used as sleeping medications. When marketed as such, diphenhydramine is found in formulas such as Tylenol PM, Sominex, Excedrin PM, and the like. Not knowing this, pilots will often take these OTC sleep aides in ways that are not safe and certainly not FAA approved. Long-haul pilots who take these medications in an attempt to counteract jet lag might not realize that they will begin another flight before the required 60 hour waiting period is over. Cockpit crew members with heavy schedules and short layovers sometimes find themselves taking these antihistamines in order to get to sleep quickly for an early wake-up call, again before enough time has lapsed for the side effects to wear off.

It is noteworthy to mention that diphenhydramine is one of the most common OTC drugs found in the tissues of pilots involved in fatal airplane accidents. There is a reason for those warning labels recommending against operating dangerous machinery while “under the influence“!

There is another category of physiologically active compounds that are neither prescriptions nor OTC drugs. These are the dietary supplements; some are reported to help reduce sleep problems, such as melatonin. The FAA generally allows airmen to use any of these supplements if they do not suffer adverse side effects from them. However, claims about these dietary supplements’ benefits in treating insomnia and “jet lag” are often overstated, and have not been substantiated in scientific double-blind studies. Some individuals actually have significant side effects from these “natural” supplements, and in the case of melatonin can even produce nightmares and other sleep disturbances. There is also concern among some scientists that melatonin might adversely affect other basic body clocks, such as reproductive cycles in women, particularly because the dosages in these pills can create concentrations in body tissues much higher than what occurs naturally. Additionally, since the Food and Drug Administration does not regulate food supplements, it is not possible to ensure the purity and dosage of these substances. Buyer, beware!

Then there is alcohol. Aside from the 8 hour “bottle to throttle” rule, alcohol is not, in fact, a decent sleep-inducing chemical. It actually interferes with natural sleep cycles and impairs the brain’s ability to refresh itself. There are also some commonly prescribed sleep medications that are not allowed by the FAA, such as Halcion due to its long half-life and potentially addictive tendencies.

So, having said all this what can a pilot use to help get to sleep on those layovers, or to help re-adjust to a normal cycle when back home?

For the past couple years, the FAA has approved the use of one prescription sleep medication, Ambien (zolpidem), by virtue of its short half-life (2.5 hours) and safe side-effect profile. Its minimum “no fly” waiting time is 24 hours. More recently, the FAA has approved another ultra short-acting sleep aide that one may fly as soon as 6 hours after ingestion – Sonata.  Here is a chart showing the waiting times of various popular sleep aides.

Trade Name Generic Name Required minimum waiting time after last dose before flying
Ambien zolpidem* 24 hours
Ambien CR zolpidem (extended release) 24 hours
Edluar zolpidem (dissolves under the tongue) 36 hours
Intermezzo zolpidem (for middle of the night awakening) 36 hours
Lunesta eszopiclone 30 hours
Restoril temazepam 72 hours
Rozerem ramelteon 24 hours
Sonata zaleplon 6 hours
Zolpimist zolpidem (as oral spray) 48 hours


As can be expected, there are some FAA regulations that pilots must be aware of when using these medications. First of all, they must wait the minimum time required before flying. Secondly, they should not be used more than once or twice a week in order to avoid habituation. It should go without saying that there are always a few individuals who will have unusual and unanticipated side effects to any medication, so a pilot should always “ground test” any new drug first during a few days that he or she will not be flying, in order to assure that unanticipated adverse effects will not occur. This rule actually applies to all OTC medications, “natural” supplements and prescriptions, which a pilot has never used before, as the time to discover unexpected side effects should not be in the cockpit! Bear in mind that no sleeping medications should be used on a regular basis to treat chronic insomnia, which is a medical condition where an individual has chronic sleep disturbance. In order to avoid habituation, these drugs should only be used intermittently for those circumstances where sleep is difficult to attain because of disrupted schedules.

Having said all this, none of the medications discussed in this article will show up on a DOT drug screen. For safety sake, you, the pilot, must be the judge!