According to the remote pilot study guide, which common over-the-counter medication ingredient is known to cause drowsiness with a prolonged half-life, making it a particular concern for a remote pilot before flying?

Why: The study guide specifically calls out diphenhydramine-containing medications such as Benadryl as "known to cause drowsiness and have a prolonged half-life, meaning the drugs stay in one's system for an extended time, which lengthens the time that side effects are present." For any new OTC or prescribed medication, the guide recommends waiting at least 48 hours after the first dose before flying.

• The study guide does not single out acetaminophen for the drowsiness and prolonged-half-life concern it attributes specifically to antihistamines like diphenhydramine.
• Caffeine is a stimulant, the opposite effect of the drowsiness concern the guide raises about antihistamines and decongestants.